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Front 1

Scleral (Haptic) Lens

Back 1

!st successful contact lens
lathe cut and made out of gas permeable material
very difficult to tolerate; used when other types fail in such cases as severe keratoconus, severe lid problems, and great amounts of astigmatism.

Front 2

Corneal Lens

Back 2

Most common design for rigid and gas perm lenses
the diameter of the lens is smaller than that of the cornea
corneal diameters range from: 10.5-12.5mm while the diameter of the lens can range from: 7.4-9.2mm

Front 3

Semi-Scleral Lens

Back 3

These lenses bridge the limbus and lie partially on the conjunctiva tissue overlying the sclera and adjacent to the cornea
typical of soft contact lenses

Front 4

Daily Wear, Extended Wear, or Prolonged Wear

Back 4

Determined by the amount of gas permeability of the material
Approved by the FDA for 30 days of consecutive wear, but FDA recommends that they be worn no longer than 7 days in a row.

Front 5

Gas Permeable Lens

Back 5

Permits the passage of oxygen and carbon dioxide through the lens

Front 6

Cosmetic Lens

Back 6

used to cover an unsightly blind eye
enhance cosmetic appearance

Front 7

Bandage Lens

Back 7

Used over the cornea to protect it from external influences which permits the healing of underlying corneal disorders

Front 8

Hydrophobic Lenses

Back 8

Made of materials which, if not specially treated, will repel water

Front 9

Hydrophilic Lenses

Back 9

Made out of materials which will naturally absorb water

Front 10

Wetting Angle

Back 10

The angle that a bead of water makes with the surface of a given material, the smaller the wetting angle the greater the wetting ability.

Front 11

PMMA- Polymethylmethacrylate (Rigid Lens)

Back 11

Hard transparent plastic
typically 8-10 mm in diameter
developed in 1947 by Kevin Touhy
"conventional hard lenses"

Advantages: Consistent vision, durable, spherical lenses can correct for up to 3.00D of corneal astigmatism, easily fabricated

Disadvantages: Hydrophobic, absorbs only 1.5% water, uncomfortable, poor gas permeability requires "pumping action" of the tear layer for adequate oxygen exchange, corneal edema/spectacle blur common

Front 12

CAB- Cellulose Acetate Butyrate (Rigid Lens)

Back 12

Developed in 1938 by Eastman Kodak as a photographic material
First used as a CL material in 1974
Wets easier than PMMA, permitting better tear flow under it
Much better gas perm than PMMA

Advantages: Increased comfort, longer wearing time, less edema/spectacle blur, elimination of edge flare because it can be fitted larger (about 9 mm), better for sports, can be fitted tighter so there is less chance of loss, very tough and difficult to break, greater gas perm, lower wetting angle.

Disadvantages: Poor shape retention (can warp after 1 year of wearing time or can change after hydration and steepen after several weeks), thicker lenses can be used to reduce chance of warpage but it increases lens awareness due to increased center and edge thickness

Front 13

Silicone-Acrylate (rigid lens)

Back 13

The next generation of rigid gas perm contact lens materials
Material Composition: Silicone (35%) and PMMA (65%)
Developed in 1979 by Syntex Opthalmics
Known clinically by the following names:
Polycon I and II
Boston Lenses I and II
Menicon O2
Optocryl 60
Paraperm
B&L Gas Perm
Prinicple Advantage over CAB: Since it is a more stable material it can be made thinner. This makes the lens more comfortable and allows for greater oxygen transmission.

Front 14

Fluorocarbon and Fluorocarbon Silicone Acrylate (rigid lens)

Back 14

highest gas permeability of all lenses.
may be made of either fluoropolymer or fluoropolymer and silicone combined.
Trade names:
Advent (Allergan/3M) 100 DK
Fluoperm 30 (Paragon) 30 DK
Fluoperm 60 (Paragon) 60 DK
Fluoperm 92 (Paragon) 92 DK
Boston Equalens (Polymer) 71 DK
Boston Equacurve (Polymer) 71 DK
Boston Equalens (Polymer) 45 DK
Fluorex (GT Laboratories) 70 DK
Quantum I (B & L) 9 DK
Quantum II (B & L) 210 DK
Boston EXPFS (Polymer) 203 DK

Front 15

DK value

Back 15

The oxygen permeability of a contact lens is characterized by its Dk value. Dk is defined as the diffusion coefficient (D) multiplied by the solubility constant (k).
The higher the DK value the better the oxygen permeability.

Front 16

HEMA- Hydroxyethylmethacrylate

Back 16

Approved by the FDA in 1971 and manufactured and marketed by Bausch and Lomb
Advantages:
Greater comfort, rapid adaptation, spectacle blur uncommon, ok to wear intermittenly, minimal lens loss, minimal overwear reaction, less flare and photophobia, corneal protection, offers an alternative for rigid lens drop outs, excellent cosmetic lens (difficult to see), better for infants and children.

Disadvantages:
spherical lenses will not significantly correct for corneal astigmatism
poor vision can result if lenses are not fitted properly or when they become dehydrated under low humidity conditions such as in a heated or air conditioned rooms or when there is inadequate tear flow.
lack of durability- average life span of daily wear lenses about two years
material is prone to protein build up
impossible to modify and difficult to verify
disinfection regiment must be strictly adhered to and can be costly.

Front 17

Overall benefits of new higher DK Fluorocarbon lenses compared with Soft Hydrogel Materials

Back 17

greater oxygen permeability increases the potential for extended wear performance
Larger tear layer allow greater exchange of fluid with each blink which results in improved venting of debris
since they are more durable than soft hydrogel lenses they require less freqent replacement
the larger lens sizes tend to mask greater degrees of corneal astigmatism without requiring a special toric lens
larger gas permeability rigid lenses are easier to insert and remove
they are more economical to maintain than hydrogel lenses
due to the general absence of porosity, there is less risk of corneal infection

Front 18

Leonardo da Vince (1508)

Back 18

Described glass contact lenses

Front 19

Rene Descartes (1636)

Back 19

Tube of water used to neutralize the cornea

Front 20

Thomas Young (1801)

Back 20

Used Descartes principle to study the eye

Front 21

John Herschel (1827)

Back 21

Described how a contact lens could be ground; concept of molding the eye

Front 22

A.E. Flick (1888)

Back 22

Described first glass lens to be worn to correct vision

Front 23

E. Kalt (1888)

Back 23

Designed and fitted glass corneal lenses. Used ophthalmometer to fit lenses.

Front 24

W. Feinbloom (1936)

Back 24

Made lens with glass central optic and plastic surround (first plastic used in contact lens)

Front 25

Mullen and Obrig (1938)

Back 25

First all-plastic (PMMA) contact lens

Front 26

N. Bier (1947)

Back 26

Fenestrated minimum-clearance haptic lens

Front 27

K. Touhy (1947)

Back 27

All-plastic corneal lens

Front 28

Butterfield (1950)

Back 28

Designed corneal lens to parallel the cornea, used peripheral curves

Front 29

Wichterle and Lim (1960)

Back 29

Hydrogel polymers for contact lenses

Front 30

What year did the FDA become involved in regulating contact lenses?

Back 30

1968

Front 31

Bausch and Lomb, Inc. (1971)

Back 31

First hydrogel lens approved in the US

Front 32

J. DeCarle (1970's)

Back 32

Extended wear with high water content hydrogel lenses

Front 33

Rynco Scientific (1970's)

Back 33

Use of CAB polymer for contact lenses

Front 34

What year was the first clinical marketing of soft silicone lenses?

Back 34

1970's

Front 35

Danker Laboratories (1978)

Back 35

US FDA approval of CAB lenses

Front 36

Syntex Ophthalmics (1979)

Back 36

US FDA approval of a PMMA silicone copolymer lens

Front 37

Bicurve lens

Back 37

contains two curves, a primary base curve and a flatter peripheral curve.
the junction of the two curves is generally blended to permit greater comfort.
the total diameter of the lens is equal to the diameter of the optic zone plus the peripheral curve widths.

Front 38

Tricurve lens

Back 38

contains two peripheral curves
the intermediate curve may be very narrow
generally tricurve lenses are relatively large (9.5mm or greater) with an optic zone of 6.5-7.5mm, just large enough to clear the maximum pupil diameter.

the peripheral curves are slightly flatter than the base curves by 0.4-0.8mm, or 2-4 diopters, and contain a width of approx. 1.3mm. The intermediate curves of a standard tricurve lens are 1mm flatter than the base curve.

Front 39

Base Curve

Back 39

The base curve of the central portion of the back surface of a contact lens.
It is also known as the central posterior curve (CPC) or the primary base curve.
The base curve is desgined to conform to the optic zone of the cornea and is measured in millimeters of radius of an arc, or in diopters.

Front 40

Radius of curvature

Back 40

the distance from the geometric center of the circle to its periphery where the line is drawn.
As the radius of curvature becomes longer the circle gets larger.
As the circle gets larger, its curve gets flatter.
As the curve gets flatter the power in diopters become less.

Front 41

Diopter to Millimeter Conversion

Back 41

45D = 7.50mm
when the power of a curve changes by 0.50D, the radius of curvature changes by approx. 0.10mm.

Formula: 337.5/___D or mm

ex. 37D
337.5/37D=9.12

ex. 9.12mm
337.5/9.12mm=37D

Front 42

sagital depth or height

Back 42

the distance between a flat surface and the back surface of the central portion of a lens.
A greater sagital depth produces greater vaulting of the lens and in effect would be steeper.
It is sometimes referred to as sagittal vault.

Front 43

Loosening and tightening of a lens

Back 43

As the diameter gets greater, the sagital depth or vaulting increases.
The greater the sagital depth, the tighter the fit of the lens.

The shorter the radius of curvature, the greater the sagital depth; the longer the radius, the shorter the sagital depth.

Front 44

Optic zone

Back 44

the central portion of a contact lens which contains the refractive power and generally corresponds to the central corneal cap.

Front 45

Posterior Apecal Radius

Back 45

This term is generally used in reference to spin cast soft lenses.
The curvature of the posterior surface of the lens changes with the refractive power. The radius of curvature is measured at the apex of the posterior surface.

Front 46

Steeper Base Curve

Back 46

Occurs when the posterior radius of curvature is decreased (8.4 to 8.1mm).

Front 47

Flatter Base Curve

Back 47

Occurs when the posterior radius of curvature is increased (8.1 to 8.4 mm).

Front 48

Lens Diameter of Chord Diameter

Back 48

The width of a lens or the measurement from one edge of the lens to the opposite edge.

Front 49

Curve Widths

Back 49

The width of the CPC, PPC, or IPC

Front 50

Central Thickness

Back 50

Separation between the anterior and posterior surface at the geometeric center of the lens.
Minus lenses are thinner, plus lenses are thicker.

Front 51

Ballasted Lens

Back 51

Lens with a heavier base which becomes oriented inferiorly or downward when the lens is worn.

Front 52

Prism Ballasted Lens

Back 52

A ballasted lens which utilizes a prism wedge designed to weight the lens.

Front 53

Truncated Lens

Back 53

A lens which has been cut off, usually 0.5-1.5mm along its lower edge, to form a horizontal base. Double truncations, along the top and bottom portion of the lens is sometimes done to help improve stabilization.

Front 54

Back Surface Power

Back 54

Effective power of a lens when measured from the back surface

Front 55

Toric Lens or Toroid Lens

Back 55

Lenses with different radii of curvature in each meridian which are used to correct astigmatism.

Front 56

Principle Meridians

Back 56

The meridians of shortest and longest radii which differ by 90 degrees

Front 57

Front surface toric lens

Back 57

A lens in which the anterior surface has two different radii and the posterior surface is spherical.

Front 58

Back surface toric lens

Back 58

A lens in which the posterior surface has two different radii and the anterior surface is spherical.

Front 59

Bitoric lens

Back 59

A lens in which both the posterior and anterior surfaces contain two different radii.

Front 60

Lenticular Bowl

Back 60

A lens design generally used in higher plus powers which consists of a central optic zone and a surrounding non-optic peripheral or "carrier" portion.
(moon shaped, thicker in the center thinner on the sides)

Front 61

Spin-cast soft lens

Back 61

A method of manufacturing soft contact lenses whereby a liquid material is revolved in a mold at a controlled speed and temperature which produces the desired curvature, design, and power.

Front 62

Lathe Cut Soft Lens

Back 62

A method of manufacturing soft contact lenses in which a machine lathe is used to grind lens designs, size, and power.

Front 63

Spherical Equivalent

Back 63

A spectacle or contact lens prescription which is expressed only as a sphere.
To calculate the sphere equivalent, algebraically add half the cylinder power to the sphere.

Front 64

The first successful contact lenses which were originally molded to conform to the shape of the cornea were known as _________ lenses.
a) corneal
b) haptic
c) interpalpebral
d) gas permeable

Back 64

b) haptic

Front 65

Corneal contact lenses:
a) are a typical design of soft lenses
b) bridge the limbus and lie partially on the conjuctiva tissue
c) are used only as a last resort when other types of contact lens design would fail
d) are the most common design for rigid and gas permeable lenses

Back 65

d) are the most common design for rigid and gas permeable lenses

Front 66

The majority of soft lenses fit today are:
a) corneal
b) haptic
c) semi-scleral
d) hyrdophobic

Back 66

c) semi-scleral

Front 67

A liquid coming in contact with a hydrophillic lens material with a relatively small wetting angle would be likely to:
a) form beads on the surface
b) quickly evaporate
c) spread evenly over its surface
d) none of the above

Back 67

c) spread evenly over the surface

Front 68

A contact lens with a diameter larger than that of the cornea is called a ________ lens.
a) corneal
b) hydrophillic
c) hydrophobic
d) haptic

Back 68

d) haptic

Front 69

All the following are symptoms of a loose fitting lens except:
a) lid sensation
b) constant awareness
c) burning
d) feeling the lens move

Back 69

c) burning

Front 70

Of the curves listed, which indicates the flattest base curve?
a) 7.50mm
b) 37.50D
c) 8.60mm
d) 49.00D

Back 70

b) 37.50D or 9mm

Front 71

A contact lens was ordered with a base curve of 7.85mm but was received back from the lab with a base curve measuring 7.80mm. The base curve of the actual lens is:
a) 0.25D flatter than the lens ordered
b) 0.25D steeper than the lens ordered
c) 0.50D steeper than the lens ordered
d) 0.50D flatter than the lens ordered

Back 71

b) 0.25 steeper than the lens ordered

Front 72

It is noticed that a rigid contact lens containing a base curve of 7.42mm is fitting quite loose. A tighter fit may be achieved by changing the base curve to:
a) 7.46
b) 7.85
c) 8.04
d) none of the above

Back 72

d) none of the above

Front 73

A contact lens has a base curve of 7.50mm. Its posterior peripheral curve would most likely be:
a) 7.45mm
b) 42.50D
c) 7.35mm
d) 30.00D

Back 73

b) 42.50D or 7.94mm

Front 74

The secondary curve of a rigid contact lens is generally:
a) steeper than the CPC
b) 1 to 2 diopters flatter than the CPC
c) 2 to 4 diopters flatter than the CPC
d) none of the above

Back 74

c) 2 to 4 diopters flatter than the CPC

Front 75

The term "haptic lens" is used in reference to:
a) a prism ballasted lens
b) a truncated lens
c) a scleral lens
d) a spin-cast lens

Back 75

c) a scleral lens

Front 76

The CPC of a contact lens measures 7.5mm radius of curvature. Its power in diopter is:
a) 41.00D
b) 43.00D
c) 45.00D
d) 47.00D

Back 76

c) 45.00D

Front 77

The fitting characteristics of a gas permeable rigid contact lens may be altered by:
a) changing the radius of curvature of the CPC
b) increasing the diameter
c) widening the PPC
d) all of the above

Back 77

d) all of the above

Front 78

A soft contact lens demonstrates excessive movement. This may be remedied by:
a) a larger diameter lens
b) a smaller diameter lens
c) a flatter lens
d) disinfecting the lens

Back 78

a) a larger diameter lens

Front 79

The term "sagittal value" refers to:
a) a poorly fitted lens
b) scleral show
c) the vaulting effect of a contact lens
d) nothing of significance

Back 79

c) the vaulting effect of the contact lens

Front 80

When determining the best lens material to use, which of the following should be considered?
a) the patients working conditions
b) precorneal tear film
c) full time vs. part time wear
d) all of the above

Back 80

d) all of the above

Front 81

The gas permeability of a CAB lens is largely dependent upon:
a) the diameter of the central posterior curve
b) the width of the posterior peripheral curve
c) the lens thickness
d) the overall diameter

Back 81

c) the lens thickness

Front 82

A rigid gas permeable lens with a base curve of 7.50mm is found to be fitting slightly tight. To improve the fit we might consider changing the base curve to which of the following?
a) 7.40
b) 7.45
c) 7.55
d)7.65

Back 82

c) 7.55

Front 83

The CPC of a rigid contact lens is held constant while the diameter is increased. This would result in:
a) a tighter fit
b) a looser fit
c) less valuting
d) increased gas permeability

Back 83

a) a tighter fit

Front 84

When compared with PMMA, CAB lenses:
a) have much better gas permeability
b) can be fit larger
c) are less likely to result in hypoxia induced corneal edema
d) all of the above

Back 84

d) all of the above

Front 85

When compared with PMMA which of the following is not true about CAB lenses?
a) they have excellent shape retention
b) they can be fit tighter
c) they can be fit larger
d) they are better for sports

Back 85

a) they have excellent shape retention

Front 86

HEMA is an abbreviation commonly used to describe:
a) rigid lenses
b) gas permeable lenses
c) soft lenses
d) corneal abrasion

Back 86

c) soft lenses

Front 87

The chief reason to utilize a ballasted lens is:
a) to correct verticle astigmatism
b) to lower the wetting angle
c) to inhibit lens rotation
d) to tighten the fit

Back 87

c) to inhibit lens rotation

Front 88

Which of the following is not true of PMMA lenses?
a) spherical lenses can correct for up to 3D of astigmatism
b) they are easily fabricated
c) they have a long history of acceptance
d) they have excellent gas permeability

Back 88

d) they have excellent has permeability

Front 89

Which of the following is not true about soft contact lenses?
a) spectacle blur is uncommon
b) there is less flare and photophobia than with "conventional" rigid lenses
c) rapid adaptation to lens wear is possible
d) spherical lenses will correct for moderate to high amounts of astigmatism

Back 89

d) spherical lenses will correct for moderate to high amounts of astigmatism.

Front 90

The central portion of the back surface of the contact lens is called:
a) the central posterior curve
b) the primary base curve
c) the base curve
d) all of the above

Back 90

d) all of the above

Front 91

The distance between a flat surface and the back surface of the central portion of a lens is the:
a) chord diameter
b) sagittal depth
c) principle meridian
d) back surface power

Back 91

b) sagittal depth

Front 92

A contact lens design which utilizes a lenticular bowl is typically employed with:
a) bitoric lenses
b) prism ballasted lenses
c) higher minus lenses
d) higher plus lenses

Back 92

d) higher plus lenses

Front 93

A loose fitting contact lens can be made to fit tighter by:
a) shortening the radius of curvature of the CPC
b) lengthening the radius of curvature of the CPC
c) decreasing the diameter
d) truncating the lens

Back 93

a) shortening the radius of curvature of the CPC

Front 94

The first all plastic corneal contact lens was developed by Kevin Tuohy in:
a) 1888
b) 1936
c) 1947
d) 1971

Back 94

c) 1947

Front 95

An example of a hydrophillic lens material is:
a) silicone-acrylate
b) CAB
c) PMMA
d) HEMA

Back 95

d) HEMA

Front 96

Bicurve rigid contact lenses are usually:
a) small and steep
b) fit within the interpalebral fissure limits
c) made with narrow peripheral curves
d) all of the above

Back 96

d) all of the above

Front 97

A contact lens in which the anterior surface contains two different radii of curvature and the posterior surface is spherical is called a ________ lens.
a) bitoric
b) front surface toric
c) back surface toric
d) bicurve

Back 97

b) front surface toric

Front 98

When the radius of curvature is held constant while the diameter is increased, the vault of the lens will be:
a) unchanged
b) increased
c) decreased
d) truncated

Back 98

b) increased

Front 99

the cornea

Back 99

has five distinct layers:
1. Epithelium (highly regenerative)
2. Bowman's membrane
3. Stroma (90% of thickness)
4. Desemet's membrane
5. Endothelium

cornea is about 0.5mm thick at the center

Front 100

tear film (function)

Back 100

its function: maintaining the optical quality of the cornea as well as the health of the cornea and conjunctiva. it passes lysozyme (an antibacterial enzyme) that inhibits bacterial proliferation.

when contacts are worn the tear film provides oxygen exhange as the lens is moved. the tear film can be shaped into a liquid lens with significant refractive power by the front surface of the cornea and the back surface of a rigid contact lens.

Front 101

layers of precorneal tear film

Back 101

3 layers: lipid, aqueous, and mucoid

Lipid layer: top or outer layer; consists of fatty material which forms a thin layer over the whole surface of the tear film; it functions primarily to prevent evaporation of the tear film; this layer is produced by the meibomian glands located in the upper and lower eyelids.

Aqueous layer: middle layer; consists of 98% water and accounts for most of the thickness; it contains ions and other molecules such as sodium and potassium along with a concentration of protein; produced by lacrimal glands which are located in the palbebral conjunctiva or the temporal portion of the upper cul de sac.

Mucoid layer: the bottom or innermost layer; located immediately against the corneal and conjunctival epithelial cells; produced by the goblet cells located in the conjunctiva; functions to convert the hydrophobic epithelial layer of the cornea to a hydrophillic surface; without this layer the tear film would break up very rapidly resulting in drying and corneal damage.

Front 102

B.U.T.

Back 102

stands for "break-up time" of tear film; assesses the quality of the tear film and is performed with flouriscein and a slit lamp.

short break up time may indicate a problem with the mucoid layer; average break-up time is 20-25 seconds; a BUT of less than 10 seconds presents a potential problem.

Front 103

Schirmer Test

Back 103

assesses the quantity of tears normally produce; performed with a strip of filter paper placed under each lid and kept there for approx. five minutes; normally there would be about 15mm or more of moistened strip; patients over 40 will find 10mm to 15mm of moistened strip.

Front 104

Rose Bengal

Back 104

Reddish-purple stain that colors degenerating and dead epithelial cells; may be used either as a paper strip or a unit dose.

Front 105

Best Prognosis (Best contact lens canidate)

Back 105

13-38 years of age
women
refractive error > -1.50 and > +1.50
K reading 41 to 46 D
BUT's > 15 seconds
cornea with no sig. sequential staining
good tear flow by Schirmer test
regular corneas (no scarring or distortion of corneal mires)
regular low astigmatism < +1.50
Good lid position with no scleral show
adequate manual dexterity

Medical factors:
Nystagmus- patients whose eyes oscillate constantly may benefit from contact lenses because the lenses move with the eye
Ocular albinism- a darkly tinted cosmetic lens with a clear aperature may be useful against the glare from which an albino suffers
Andridia- a congenital abscence of the iris. these patients are sometimes more comfortable with tinted cosmetic lenses

Front 106

reduced prognosis for successful fitting

Back 106

small refractive errors (less than + or - 1.25 diopters)
certain occupations: factory workers, hair dressers, chemical environments
pre-presbyopes- myopes who are about to become presbyopic
those with excessive fears about having a foreign object touch their eyes
if follow-up visits are not possible
poorly motivated patients
smokers
those who suffer with allergies, chronic blepharitis, arthritus or exophthalmos

Medical factors:
skin disease
systemic drugs that reduce tear flow (birth control)
arthritis or parkinsonian-like tremor
corneal disease or allergies
corneal warpage and corneal anesthesia
the monocular patient
pregnancy and menopause can effect the quality of the tear film
unstable diabetes

Front 107

vertex distance

Back 107

the distance from the front of the cornea to the ocular surface of the lens is called the vertex distance; as the relative position of the focal point changes the effective power of the lens is changed.

the changes only become significant for contact lenses when the lens powers exceed + or - 4.00 D

Rule of thumb: the effective power of a 10D lens moved a distance of 5mm will change by approx. 0.50D
If it moves closer the effective power goes down, if it moves farther away the effective power goes up.

Front 108

keratometer

Back 108

used primarily to measure the curvature of the cornea
it measures about 2-4mm of the corneal cap
the corneal cap itself is about 4-5mm in diameter

Front 109

topogometer

Back 109

an attachment to the keratometer which is a movable light designed to pinpoint the specific location of the corneal cap to be measured by the keratometer.

Front 110

placido's disc

Back 110

instrument that assess the regularity of the cornea
concentric circle are reflected off the corneal surface can indicate the presence of corneal or irregular astigmatism.

Front 111

contact lens fit "on K"

Back 111

the base curve of the lens parallels the curvature of the cornea
the power of the tear lens is plano
when there is astigmatism a lens fits "on K" parallels the flatter of the two corneal meridians

Front 112

contact lens fit steeper than K

Back 112

lacrimal lens with have plus power
tear lens is thicker in the center and thinner on the edges

Front 113

contact lens fit flatter than K

Back 113

tear lens is thicker on the edges and thinner in the center
lacrimal lens will contain minus power

Front 114

-3.25 K: 43.50 vertex distance=12mm
what would be the power of a rigid contact lens which is fit on K?

Back 114

Base curve= 43.50
Power of lens: -3.25

*since the power at the spectacle plane is less than -4.00 it is not necessary to compensate for vertex distance.

Front 115

-3.25 K: 43.50 vertex distance= 12mm
what is the power of a rigid contact lens fit 0.50D steeper than K?

Back 115

Base curve: 44.00 (43.50 + 0.50 = 44.00)
Tear lens: +0.50D
Power of lens: -3.75 (-3.75 + +0.50 = -3.25)

Front 116

-3.25 K: 43.50 vertex distance= 12mm
what is the power of a rigid contact lens fit 0.25D flatter than K?

Back 116

Base curve: 43.25
Tear lens: -0.25D
Power of lens: -3.00 (-3.00 + -0.25= -3.25)

Front 117

Spectacle Rx: -6.75 -1.00 x 180
K: 44.50/45.50
vertex distance: 12mm

What is the power of a rigid contact lens fit on K?

Back 117

* in the rx we can see that there is 1D of cylinder. looking at the K readings we can see there is 1D of toricity in the front surface of the cornea. all astigmatism is found in the cornea (no residual astig is present) when this occurs it is often possible to completely correct the corneal astigmatism using a spherical rigid contact lens. To achieve this we must:
1) transpose the rx to minus cyl form (already done in this example)
2) drop the cyl and axis

so we are left with -6.75

since the power is greater than -4.00D it is necessary to compensate for vertex distance.
(when we look at the table a -6.75 diopter spectacle lens at 12mm would need to be compensated at -6.24, rounded off this gives us -6.25.
what this means is that the power of the contact lens plus the tear lens needs to equal -6.25D

Base curve: 44.50
Power of lens: -6.25D

Front 118

Spectacle Rx: -6.75 -1.00 x 180
K: 44.50/45.50
vertex distance: 12mm

what is the power of a rigid contact lens fit 0.50K stepper than K?

Back 118

1) drop cyl and axis
2) we are left wiht -6.75
3) since it is greater than -4.00D compensate for vertex distance: -6.25
4) tear lens is +0.50D

Power of lens: -6.75 (-6.25 + +0.50 = -6.25)
Base curve: 45.00

Front 119

Rx: -7.50 -1.50 X 180
K: 44.00/ 45.50
VD: 10mm

find the base curve, power of tear lens, and power of contact lens fit 0.50D flatter than K?

Back 119

Tear lens: -0.50D
Base curve: 43.50
Power of lens: -6.50 (-7.00 after compensated for VD and then -6.50 + -0.50 = -7.00)

Front 120

The tear film consists of which of the following:
1. aqueous layer
2. conjunctiva
3. lipid film
4. mucin film

a) 1 only
b) 1, 3, and 4
c) 2 and 4 only
d) 1, 2, 3, and 4

Back 120

b) 1, 3, and 4

Front 121

The primary function of the mucin film is to:

a) prevent evaporation of the tear film
b) provide oxygen exhange
c) change the corneal epithelial surface from a hydrophobic surface to a hydrophillic surface
d) aid in the prevention of "dry eye" syndrome

Back 121

c) change the corneal epithelial surface from a hydrophobic surface to a hydrophillic surface

Front 122

the lipid layer functions primarily to:

a) change the corneal epithelial surface from hydrophobic to hydrophillic
b) provide oxygen exhange
c) prevent evaporation of the tear film
d) supply nutrients to the cornea

Back 122

c) prevent evaporation of the tear film

Front 123

The test which assesses the QUANTITY of tears normally produced is:

a) BUT
b) Rose bengal
c) Schirmer
d) stereopsis

Back 123

c) Schirmer

Front 124

The test which assesses the QUALITY of the tear film is:

a) BUT
b) Rose bengal
c) Schirmer
d) stereopsis

Back 124

a) BUT

Front 125

prospective patients who fall within the following age group generally provide the best prognosis for successful contact lens fitting:

a) 42 to 65
b) 13 to 38
c) 25 to 45
d) over 45

Back 125

b) 13 to 38

Front 126

Which of the following would indicate a good prognosis for successful contact lens fitting?

1. adequate manual dexterity
2. regular low astigmatism
3. refractive error less than + or - 1.50 D
4. BUTs longer than 15 seconds

a) 1 and 2
b) 2 and 4
c) 1, 2, and 4
d) 1, 2, 3, and 4

Back 126

c) 1, 2, and 4

Front 127

The base curve of a certain contact lens is equal to 7.5mm radius of curvature. The equivalent power in diopters is:

a) 42.00
b) 45.00
c) 48.00
d) 51.00
c) 48.00

Back 127

b) 45.00

Front 128

The primary function of a keratometer is to:

a) measure the curvature of the cornea
b) test for visual acuity
c) measure intraocular pressure
d) evaluate degenerating corneal epithelial cells

Back 128

a) measure the curvature of the cornea

Front 129

when moved 5mm from its original position the effective power of a 10.00D lens will change:

a) 0.25D
b) 0.50D
c) 0.75D
d) 1.00D

Back 129

b) 0.50D

Front 130

When a spectacle lens prescription exceeds ______ diopters, vertex distance must be compensated when determining the power of a contact lens.

a) 2.00D
b) 4.00D
c) 6.00D
d) 8.00D

Back 130

b) 4.00D

Front 131

A spectacle lens is prescribed at -10.00D. Provided that the lens is fit at a vertesx distance of 10mm. A rigid contact lens fit on K for this patient would require a power of:

a) -12.00D
b) -11.00D
c) -10.00D
d) -9.00D

Back 131

d) -9.00D

Front 132

Spectacle Rx = +10.00D
VD= 10mm

A rigid contact lens fit on K would require the following power:
a) +12.00D
b) +11.00D
c) +10.00D
d) +9.00D

Back 132

b) +11.00D

Front 133

Rx: -4.00 +1.00 x 90
K: 42.50 at 180/43.50 at 90

A rigid contact lens fit on K would require the following power:
a) -2.00D
b) -3.00D
c) -4.00D
d) -5.00D

Back 133

b) -3.00D

Front 134

The power of the lacrimal lens in the previous question is:
a) plano
b) +0.50D
c) -0.50D
d) none of the above

Back 134

a) plano

Front 135

vertex distance formula

Back 135

Remember that a lens gains minus power as it is moved closer to the eye, a lens gains plus power as it is moved away.

The formula is:
(D2 X d) / 1000

so for -6.75D at a VD of 12mm
6.75^2 x 12/1000 =0.55

So you have a 0.50 diopter of change. Since it is minus it will gain 0.50 D, so you want to take the 0.50 D away. -6.25 D

Front 136

+11.00 +1.00 x 20 VD=12mm
Ks: 46.25/47.25

What would be the power of a rigid contact lens fit on K?

Back 136

+14.00D

Front 137

The transition zone between the sclera and the cornea is called:

a) stroma
b) primary curve
c) limbal area
d) ciliary process

Back 137

c) limbal area

Front 138

Moderate to high myopes often provide a good prognosis for contact lens wear. This may be because:

a) they are highly motivated
b) peripheral vision is improved
c) the image size is larger
d) all of the above

Back 138

d) all of the above

Front 139

Rx: -3.00 -0.50 x 90 VD=11

what is the power of a rigid contact lens fit 0.50D steeper than the flattest corneal meridian? Assume all the astigmatism is in the cornea?

Back 139

-3.50D

Front 140

Rx: -2.50 +0.25 x 90 VD= 12mm

If the contact lens is to be fit 0.75D steeper than the flattest corneal meridian, what would the power be? Assume all the astigmatism is in the cornea.

Back 140

-3.00D

Front 141

the thickness and power of the lacrimal lens will vary with the:

a) lens thickness
b) K readings
c) lens-cornea relationship
d) refraction

Back 141

c) lens-cornea relationship

Front 142

The precorneal tear film provides:

1. a lubricant to the cornea
2. a smooth optical surface for the cornea
3. nutrients to the cornea
4. carbon dioxide

a) 1
b) 1 and 2
c) 1, 2, and 3
d) 1, 2, 3, and 4

Back 142

c) 1, 2, and 3

Front 143

The corneal curvature at the limbal area closely approximates the curvature of the:

a) sclera
b) crystalline lens
c) corneal apex
d) macula

Back 143

a) sclera

Front 144

The CPC of a trial contact lens is 44.00D and contains a power equal to +14.87D. The over refraction is equal to
-1.62D. What final lens power is required if the CPC to be ordered is 43.62.

Back 144

+14.87 - 1.62 = +13.25
+13.25 + +0.37 = +13.62

+13.62

Front 145

A -3.50D lens with a base curve of 44.50 provides excellent visual acuity. If the CPC were changed to 45.00D what power would be needed?

Back 145

-4.00D

Front 146

A "dry eye" condition can be evaluated through which of the following tests?

a) artificial tears
b) rose bengal
c) schirmer test
d) flourescein

Back 146

c) schirmer test

Front 147

A new contact lens wearer should become familiar with the:

a) function of the retina
b) corneal vascular system
c) accomodative/convergence ratio
d) blinking mechanism

Back 147

d) blinking mechanism

Front 148

The pre-corneal tear film provides:

1. an optical surface
2. metabolic nutrients
3. endothelial reflex
4. limbal hypermia

a) 1 and 3
b) 1 and 2
c) 2 and 3
d) 3 and 4

Back 148

b) 1 and 2

Front 149

The normal cornea is in a constant state of dehydration also known as detergence. The layer of the cornea most responsible for maintaining this function is:

a) the endothelium
b) the basal membrane
c) the epithelium
d) Bowman's membrane

Back 149

a) the endothelium

Front 150

Rx: -3.25 -1.00 x 180
Ks: 44.25 x 180/45.25 x 90
VD= 12mm

The correct design of the CPC and power of the contact lens fitting on K would be?

Back 150

CPC= 44.25
Power of lens: -3.25

Front 151

Rx: -3.25 -1.00 x 180
Ks: 44.25 x 180/45.25 x 90
VD= 12mm

The correct design of the CPC and power of a contact lens fitting 0.50 steeper than K would be?

Back 151

CPC= 44.75
Power of lens: -3.75

Front 152

Rx: -3.25 -1.00 x 180
Ks: 44.25 x 180/45.25 x 90
VD= 12mm

The correct design of the CPC and power of a contact lens fitting 0.25 flatter than K would be?

Back 152

CPC= 44.00
Power of lens: -3.00

Front 153

Rx: -3.25 -1.00 x 180
Ks: 44.25 x 180/45.25 x 90
VD= 12mm

The correct design of the CPC and power of a contact lens fitting 0.50 flatter than K would be?

Back 153

CPC: 43.75
Power of lens: -2.75

Front 154

There are two broad categories of rigid contact lenses: _______________ lens and the larger ______ _____________ lens.

Back 154

Palpebral
Lid Attachment

Front 155

The palberal lens (characteristics)

Back 155

small and thin: small enough to be contained within the cornea with little of no contact with the upper or lower lids.
diameters usually range from 7.8 to 8.6mm.
with each blink the lens moves up and approaches the superior limbus.
Between blinks, in ideal cases, it falls slowly toward the inferior limbus lowering to just below the center.
Thicknesses are generally in the range of 0.08 and 0.12mm and the peripheral curves are relatively steep.

The lenses should be large enough to provide a minimal sense of motion during blinking producing as little glare as possible.
However two large of a lens can result in reduced comfort.
The thinness of the lens results in some flexure with each blink which creates a tear pump that can help with tear exchange.

Front 156

Palberal Lens: Advantages

Back 156

1. It provides excellent tear exchange resulting in minimal corneal edema and spectacle blur.
2. Eye movement is free from lid irritation since the lens is smaller than the palpebral fissure.
3. The thinner lenses are much more comfortable than conventional lenses and can therefore be employed as a possible alternative to soft lenses especially when a significant amount of corneal astigmatism is present.
4. A high riding rigid lens problem may be solved through the use of the small microthin lenses which may center better.
5. Patients who have induced corneal astigmatism caused by the "molding" effect of larger lenses may benefit from a smaller microthin lens.

Front 157

Palbebral Lens: Disadvantages

Back 157

1. The interpalpebral lens should not be used where the lens is likely to be high riding, such as in severe myopia. Their thinness can actually carry the lenses higher.
2. They can be difficult to remove. Their thin edge makes it difficult for the upper lid to dislodge the lens.
3. In cases of high corneal astigmatism, they dont center particularly well.
4. They warp relatively easily, are difficult to modify because of their size, and because of their thinness, they are easier to damage or break in handling.
5. Patients with large pupils often complain of "flare".

Front 158

Lid Attachment Lens: Characteristics

Back 158

Lens diameter is approximately 9-10mm and contains a large optic zone of 7-8mm.
It often assumes the shape of a tricurve lens with the radius of the intermediate curve 1mm flatter than the base curve and the radius of the peripheral curve 1mm flatter than that of the intermediate curve.
With blinking the lens attaches to the upper lid and is lifted high and may even override the superior limbus.
A high riding lens may also be achieved through the use of a minus carrier.
A larger lens of this type may be indicated by a flat, large cornea (over 11mm or flatter than 44.00D, or by a large palpebral aperature of 10mm or greater).
It can also be useful when smaller lenses result in poor centration.
When made of PMMA, these lenses can only be tolerated by about 20-30% of patients. However considerably greater success is achieved when the newer gas permeable materials are used.

Front 159

Lid Attachment Lens: Advantages

Back 159

1. The large optic zone can minimize or eliminate the annoying flare often seen with smaller lenses.
2. The wider peripheral curves hold a large reservoir or tear fluid that aids in cushioning the lens and assists in tear exchange.
3. The larger size enables the lens edge to remain under the upper lid during blinking.
4. Spherical lenses can correct for up to 3.00 to 4.00D of corneal astigmatism.
5. The lenses center well, are stable, and are easy to handle.

Front 160

Lid Attachment Lens: Disadvantages

Back 160

1. There is an increased risk of corneal molding due to the bulk of the lens which can induce up to 5.00 to 6.00D of corneal astigmatism.
2. Not practical for patients with small palprebral fissures, or small steep corneas.
3. Lenses can only be tolerated by about 20-30% of patients. Although it is less comfortable at first, a surprising degree of adaption can be achieved after a few weeks.
4. Peripheral curves must be precisely designed or lenses can become very loose.

Front 161

Trial Lens Method or "Diagnostic Lens" Method (Fitting Method)

Back 161

The most accurate method of fitting contact lenses. It allows for a close estimate of proper lens size, power, and curvature and it enables the fitter evaluate what if any edge modifications may be necessary.
Also allows the wearer to evaluate their sensitivity to hard lenses.

Trial lenses are generally composed of PMMA, however some gas permeable materials such as CAB are lighter in weight and this needs to be taken into account

Front 162

Dyer Chart Method (Fitting Method)

Back 162

Base Curve: find the flattest corneal meridian in the left hand column of the chart. Then locate the amount of corneal astigmatism in the column to the right. Note the base curve indicated.

Diameter, Optical Zone, and Peripheral Curve: Once the base curve is determined, refer the Dyer chart for other lens parameters and find the base curve in the left hand column. Note the other parameters indicated.

Power: To calculate the correct power of a rigid contact lens, first convert the Rx to minus cylinder form. Drop the cyl and axis. If necessary, compensate for vd. The resultant sphere power would then correspond to the power of the lens.

Front 163

Hartstein Modification (Fitting Methods)

Back 163

Uses two basic parameters to arrive at the dimensions of the contact lens - corneal diameter and pupillary size.

Lens Diameter: To determine the lens diameter, add 4mm to the size of the pupillary diameter. In the case of larger corneas (12mm or more) add 0.5mm to the overall diameter. For smaller corneas (10mm or less) reduce the diameter by 0.5.

Optic Zone: The size of the optic zone is 1.5mm smaller than the overall lens diameter.

Secondary Curve: Should be 0.75mm wider than the base curve and 5.00D flatter.

Thickness: The standard thickness for a plano lens is 0.16mm. For each diopter of minus power, 0.01mm is subtracted from the center thickness. For each diopter of plus power, 0.02mm is added to the center thickness.

Base Curve: The base curve is fit 0.25 to 0.50 steeper than K. If there is between 0.50 and 2.00 D of corneal astigmatism, a spherical lens is ordered parallel to the flattest corneal meridian or on K. If the corneal astigmatism falls between 2 and 3D, it would require a lens 0.50 steeper than K. Any astigmatism over 3D would indicate the use of a toric contact lens.

Front 164

Flourescein Patterns (Rigid Lens Evaluation)

Back 164

Flourescein is a common dye or stain whcih can be used to help analyze the fit of a rigid contact lens.
When it mixes with the tear film it will glow in the presence of ultraviolet light or cobalt blue light.
It allows the fitter to examine the shape and flow of the tear layer between the back surface of the lens and the front surface of the cornea. It is avaliable in solution form or impregnated strips.

Front 165

With the rule astigmatism

Back 165

the verticle meridian has the steeper curve
the lens will pull up or down when blinking

Front 166

against the rule astigmatism

Back 166

the horizontal meridian has the steeper curvature
the lens will move from left to right when blinking

Front 167

Soft Lens Fitting (General Characteristics)

Back 167

Soft lenses are actually semi-scleral or corneoscleral lenses that fit over the cornea and sclera simultaneously.
Due to the hydrated plastic material they are inherently gas permeable. The cornea can breathe primarily through the lens matrix and to a lesser degree by the tear pump action which is created as the lens flexes during blinks.
Soft lenses move less during the blink cycle than rigid lenses. The amount of movement will increase with thicker lenses.
In general they are more comfortable than rigid lenses, provided that there is no lens compression along the limbal area since the lens is continually in contact with this area.

Front 168

Soft Lens Fitting (Fitting Goals)

Back 168

The lens should not be fit too tight. A tight fit could result in pain and redness within a just a few minutes since it causes the limbal vessels to become compressed due to tissue edema at the edge of the lens.
The lens should center well allowing the limbus to be completely covered at all times during blinking. When spin cast lenses are used, they are generally fit about 2mm larger than the horizontal visible iris diameter.
The lens should be left on the eye for at least 15 minutes before making a final decision reguarding the parameters. This allows the lens to conform to the pH, temp, and osmolarity of the eye.
K readings are not as important as with hard lenses, but should always be taken. It provides a baseline measurement of the corneal curvature and will provide a rough idea as to whether a flatter or steeper lens should be tried first.
Generally soft lenses are avaliable in three base curves.

Front 169

Soft Lens Fitting (Spherical Equivalent)

Back 169

Spherical soft lenses are often fit even when a relatively low amount of astigmatism is present. For example:
-3.50 -0.50 x 180
a spherical soft contact lens with a power of -3.75 could be indicated.
This power is known as the spherical equivalent and is derived by algebraically adding half the cyl power to the sphere.

Front 170

Soft Lens Fitting (Characteristics of a Good-Fitting Lens)

Back 170

The three point touch: the lens should rest lightly on the apex and the peripheral areas of the cornea.

Good centration: after blinking the rim of the lens should not show more on one side of the cornea than the other.

There needs to be adequate movement: A standard thickness should about 0.5 to 1.0mm while gazing upward after a blink. Thinner lenses are generally fit tighter and less than 0.5mm of movement is acceptable due to the greater oxygen permeability of the thinner lens.

Stable vision should be achieved: visual acuity should be as sharp as possible and remain equally clear before and immediately after the blink.

Crisp retinoscopic reflex: A soft lens is fitting well when the retinoscope streak or spot is as sharp and crisp before and after blinking as it would be if there were no lens in place.

Clear and undistorted keratometry mires: These mires should remain clear and undistorted both before and after a blink.

Front 171

Rigid Lens Verification

Back 171

Diameter: The lens diameter can be verified with a measuring hand magnifier, a diameter gauge, or one of the various types of projector inspection devices. Tolerance is within 0.05mm.

Surface Quality and Edges: Can be assessed by using a measuring magnifier, or through the use of the slit lamp.

Base Curve: Most often measured using a radiuscope. Base curve can also be measured using a keratometer with a special holder which allows the contact lens to be held horizontally while the keratometer remains in its normal position; the holder is called a Con-ta-chek. The base curve should be accurate to within 0.025mm.

Power: Back vertex power is measured with a lensometer. Should be within 0.25 of power specified with less than 0.12D of uncalled for astigmatism.

Thickness: Measured with a thickness gauge.

Blend and Transition Zones: May be examined through the use of a hand magnifier, projector inspection device, or a slit lamp.

Front 172

Soft Lens Verification

Back 172

The following parameters of a soft lens can be verified: Diameter, Base Curve, Power

The methods for verification of soft lenses cannot be relied upon for complete accuracy. Best method of verification is insertion and then inspecting them carefully on the eye.

Diameter: May be measured with a hand magnifier which allows the soft lens to contour itself to the magnifier.

Base Curve: Can be measured on templates of known radii of curvature. Can be measured on a Soft Lens Analyzer which can also be used to measure diameter, center thickness, and can provide close surface and edge inspection.

Power: Can be measured using a lensometer. A water cell may also be used to measure the power of soft lens in the hydrated state. The lensometer reading is multiplied by a factor of four. Not a reliable method since the power can vary with the thickness of the lens.

Front 173

The power of a lens is generally specified:

a) in front vertex power
b) in back vertex power
c) in keratometry readings
d) while the lens is on the eye

Back 173

b) in back vertex power

Front 174

It is possible to assess the quality of the peripheral curves of a rigid contact lens through the use of:

a) shadowgraph
b) burton light
c) keratometer
d) profile analyzer

Back 174

a) shadowgraph

Front 175

A flourescein pattern with a rigid contact lens in place shows a narrow band horizontally, with a concentration of flourescein under the lens both inferiorly and superiorly. The type of astigmatism represented by this pattern is:

a) with the rule astigmatism
b) against the rule astigmatism
c) oblique astigmatism
d) residual astigmatism

Back 175

a) with the rule astigmatism

Front 176

The lens diameter, optic zone width, and peripheral curve width may be verified simultaneously through the use of:

a) radiuscope
b) measuring magnifier
c) profile analyzer
d) keratometer

Back 176

b) measuring magnifier

Front 177

Analysis or evaluation of which of the following will help determine the best contact lens diameter:

a) trial lenses
b) HVID
c) Dyer Nomogram
d) corneal topography
d) all the above

Back 177

d) all the above

Front 178

Your patient is wearing a rigid contact lens in her right eye. It has a power of +3.00D and a base curve of 43.25. If the doctor refracts -0.50 sphere over this lens and a new lens is to be ordered with a base curve of 43.00, what will the new power need to be?

a) +3.75
b) +3.25
c) +3.00
d) +2.75

Back 178

d) +2.75

Front 179

Using the Dyer Nomogram as a guide, which of the following would not represent a realistic K reading/lens diameter relationship?

a) 43.25/44.25/lens diameter: 8.6
b) 48.25/49.25/lens diameter: 7.7
c) 40.00/41.00/lens diameter: 9.2
d) 40.00/41.00/ lens diameter: 8.2

Back 179

d) 40.00/41.00/lens diameter: 8.2

Front 180

Rx: -3.25-0.75x180
Ks: 43.50 at 180/44.25 at 90

Which of the following set of lens parameters would most simulate a RGP interpalpebral fitting?

a) 43.00 -2.75 8.6
b) 44.00 -3.75 8.6
c) 44.00 -3.75 9.6
d) 43.00 -2.75 8.6

Back 180

b) 44.00 -3.75 8.6

Front 181

Rx: -2.00 -0.50 x 180
Ks: 42.50 at 180/ 43.50 at 90

Which of the following set of lens parameters would most simulate a lid attachment RGP fitting?

a) 43.50 -3.00 9.6
b) 42.00 -1.50 9.6
c) 43.00 -2.50 8.6
d) 43.50 -3.00 8.3

Back 181

b) 42.00 -1.50 9.6

Front 182

Contact lens diameter may be most accurately measured using a:

a) millimeter ruler
b) measuring magnifier
c) radiuscope
d) lensometer

Back 182

b) measuring magnifier

Front 183

A dynamic flourescein pattern is best illuminated by:

a) indirect light
b) cobalt blue light
c) pen light
d) fixation light

Back 183

b) cobalt blue light

Front 184

When a keratometer is used to help evaluate the fit of a soft contact lens, distorted mires would most often indicate that the lens is:

a) too flat
b) too steep
c) an ideal fit
d) just slightly flat

Back 184

b) too steep

Front 185

A radiuscope is designed to:

1. inspect surface quality
2. measure radius of curvature
3. measure lens power
4. measure lens diameter

a) 1 and 3
b) 1 and 2
c) 2 and 3
d) 2 and 4

Back 185

b) 1 and 2

Front 186

The quality of the surface of a rigid contact lens may be inspected utilizing:

a) slit lamp
b) lensometer
c) measuring magnifier
d) burton lamp
e) a and c
f) c and d

Back 186

e) a and c

Front 187

The health of the cornea in an RGP fitting is dependent upon which of the following?

1. gas permeability of lens
2. size of palebral fissure
3. overall corneal diameter
4. lens/cornea relationship and movement

a) 1 and 4
b) 1 only
c) 2 and 3
d) 1, 2, 3 and 4

Back 187

a) 1 and 4

Front 188

The primary source of oxygen for the cornea is:

a) basal membrane
b) endothelium
c) tears
d) atmosphere

Back 188

c) tears

Front 189

After being placed on the patients cornea, it is observed that a soft contact lens is demonstrating edge lift. This can be corrected by:

a) decreasing the diameter
b) shortening the radius of the base curve
c) lengthening the radius of the base curve
d) altering the edge design

Back 189

b) shortening the radius of the base curve

Front 190

The base curve of a rigid lens was ordered at 7.85 mm and was received measuring 7.95 mm. This lens is ________ than ordered.

Back 190

0.50D flatter

Front 191

Concentric circles reflected off a patients cornea can be evaluated using a ____________.

Back 191

placido's disc

Front 192

When a rigid lens shows apical touch, this would indicate a:

a) steep fit
b) flat fit
c) astigmatism fit
d) perfect fit

Back 192

b) flat fit

Front 193

A rigid lens showing a band-shaped area of touch on the flattest corneal meridian indicates:

a) astigmatic fit
b) flat fit
c) alignment fit
d) steep fit

Back 193

a) astigmatic fit

Front 194

Which of the following is not an advantage of rigid palpebral lenses?

a) eye movement is free from lid irritation
b) they are easy to remove
c) they result in minimal spectacle blur
d) they can provide excellent tear exchange

Back 194

b) they are easy to remove

Front 195

Which is true about rigid, high-riding lid attachment lenses?

1. They can be useful when poor centration is noted with smaller lenses
2. Annoying flare can be minimized due to the larger optic zone
3. They are an excellent design for small steep corneas
4. Spherical lenses can generally correct for up to 3.00 to 4.00D of corneal astigmatism

a) 1, 2, and 4
b) 1, 3, and 4
c) 2, 3, and 4
d) 1 and 3

Back 195

a) 1, 2, and 4

Front 196

A well fit soft contact lens will demonstrate:

a) 3 point touch
b) good centration
c) adequate movement
d) all of the above

Back 196

d) all of the above

Front 197

In evaluating the fit of a pair of soft lenses with a keratometer, it is observed that the mires are blurry when the lenses are in place. However, after each blink the mires become clear temporarily, then blurry again. This indicates:

a) an excellent fit
b) a loose fitting lens
c) a tight fitting lens
d) 3 point touch

Back 197

c) a tight fitting lens

Front 198

An "ideal" flourescein pattern for a spherical lens on a spherical cornea would show:

a) intermediate zone touch and a thin peripheral rim
b) an even distribution of flourescein with added thickness under the peripheral curves
c) diminished dye in the center with accentuated flourescein under the peripheral curves
d) none of the above

Back 198

b) an even distribution of flourescein with added thickness under the peripheral curves

Front 199

Your patient is wearing a rigid lens with a base curve of 42.50 and a power of -3.25D. The doctor over refracts -0.75 over this lens. If the final lens to be ordered will have a base curve of 42.25, what will its power have to be?

a) -3.25
b) -3.50
c) -3.75
d) -4.00

Back 199

c) -3.75

-3.25 + -0.75 = -4.00
-4.00 + +0.25 = -3.75

Front 200

In evaluating the fit of a soft contact lens with either keratometry mires or a retinoscopic reflex, distortion immediately following each blink is detected. This would be caused by:

a) a properly fitting lens
b) a tight fitting lens
c) a loose fitting lens
d) a steep fitting lens

Back 200

c) a loose fitting lens

Front 201

Tear Film - Three Layers

Back 201

Lipid layer: a fatty material produced by the meibomian glands which forms a very thin layer over the entire surface of the tear film. It functions primarily to prevent rapid evaporation which would result in dry areas on the cornea and subsequent discomfort and corneal damage.

The Mucoid Layer: functions to convert the hydrophobic epithelial layer of the cornea to a hydrophillic surface. It is the innermost layer of the tear film and located immediately against the corneal and conjunctival epithelial cells.
BUT of Break Up Time, indicates the amount of time it takes from a blink until the tear breaks up or becomes discontinuous. BUT's shorter than 5-10 seconds are considered abnormal. Short BUT's may indicate a problem with the mucoid layer.

The Aqueous Layer: The middle layer of the tear film and consists of 98% water. However, it also contains ions and other molecules such as sodium and potassium along with a concentration of protein. A cornea is said to be hypotonic when more water flows in than out causing the cornea to swell. This occurs when normal evaporation is not allowed to occur. An isotonic cornea allows an equal amount of water to flow in as well as out allowing the cornea to maintain its normal thickness.
Another aspect of the tear layer film which you may need to know is its pH. The pH of the human tear is approximately equal to 7.4.

Front 202

The cornea

Back 202

The cornea is the anterior refracting surface of the eye. It consists of transparent tissue and is devoid of blood vessels. Ther cornea is of utmost importance to the contact lens fitter since the lens sits directly on this tissue.
The average corneal thickness is about 0.52 mm at the center and increases to about 0.65mm at the limbal area and it is composed of 5 distinct layers.

A normal cornea is in a continual state of partial dehydration which also known as deturgence. If more water flows out than water flows in the cornea becomes hypertonic resulting in corneal thinning.
Hypertonicity can be caused by a higher salt concentration placed on the cornea.

Front 203

Eyelids

Back 203

The eyelids function primarily to help keep the eye moist and to help keep out foreign bodies. It is the opposing action of the eyelids which causes tears to spread evenly over the cornea thus keeping it moist.
The lids play an important role in the fitting and wear of contact lenses for the following reasons:
a) The effect the wettability of the lens surface
b) They effect the positioning of the lens
c) They are sensitive and generally cause most of the discomfort when a lens is first placed on the eye

Front 204

Conjunctiva

Back 204

The conjunctiva is the loose tissue covering the sclera and inside the lids.
The bulbar conjunctiva covers the sclera while the palpebral conjunctiva is that portion which lines the inner surface of the upper and lower eyelids.

Front 205

5 Layers of the Cornea

Back 205

1. Epithelium: The layer of the cornea which is exposed to the tears and comprises about 10% of the total corneal thickness. It is highly regenerative. Can heal in a 24 hour period.

2. Bowman's Membrane: essentially a modification of the underlining stroma. Unlike the epithelium, if damaged by a scratch or a cut, it cannot regenerate itself so scarring will occur

3. Stroma: comprises approximately 90% of the corneal thickness. It consists of 200 to 250 layers of cells called lamellae, which lie parallel to the corneal surface. If damaged by injury, scarring will occur which can result in opacities of the cornea.
Chronic infection or corneal edema can cause blood vessels to invade the stroma resulting in a condition known as neovascularization. These blood vessels which enter to supply oxygen and nutrients can obscure vision.

4. Descemet's Membrane: a strong structureless layer which is secreted by the endothelium. It is elastic, and resistant to trauma and pathology.

5. Endothelium: the innermost or most posterior layer of the cornea, consisting of a single layer of flattened cells. In contrast to Descemet's Membrane, these cells are very susceptible to trauma and pathology. And in marked contrast to the epithelium, endothelium cells are infrequently, if ever, replaced as a normal process during adult life. It disrupted they can be replaced by the spreading of healthy cells.

Front 206

Limbus

Back 206

The limbus is the transtition zone between the cornea and sclera. It is approx. 1mm wide and the cornea is dependent upon it for receiving part of its nutrients. The limbal region becomes significant when fitting contact lenses since it is so closely connected to the cornea and some contact lenses will bear directly on it.

Front 207

Corneal Edema

Back 207

When the combination of forces which normally serve to dehyrdrate the cornea are overcome by the forces that drive water into the cornea, corneal edema may result.

This situation which may be induced by contact lens wear when the corneal epithelium becomes deprived of its normal amount of oxygen, is known as corneal hypoxia. When PMMA lenses are worn, the amount of oxygen received by the cornea is dependent upon the adequate circulation of tears under the lens. An inadequate tear flow under the lens can result in corneal edema.

Front 208

Corneal Edema (PMMA lenses)

Back 208

Abnormalities in the tear film
A tight fitting lens
An excessively large lens
poor blinking habits
inconsistent or excessive wearing time

Front 209

Corneal Edema (Rigid Gas-Perm Lenses)

Back 209

In rigid gas permeable lenses corneal edema can be caused by all of the factors as in PMMA lenses but only if there is inadequate transmission of oxygen through the lens. This can occur if the surface of the lens is coated extensively with deposits.

Front 210

Corneal Edema (Soft Lenses)

Back 210

Any factor which limits the transmission of oxygen through the lens can result in corneal edema with soft lenses. Some of these factors might include:
inadequate lid closure
excessive lens thickness
relatively low lens water content

Front 211

Corneal Epithelial Edema

Back 211

This condition appears as a grey cornea and may be best observed with a slit lamp utilizing sclerotic scatter illumination and the unaided eye.
Rated on a scale of 1-4, 4 being the worst.

Front 212

Microcystic Edema

Back 212

Progressive corneal hypoxia can lead to the rupture of certain epithelial cell membranes which in turn can result in the formation of microcysts. Microcysts are the result of fluid which has accumulated in the spaces caused by the rupture of these cells. Microcystic edema can be best seen by utilizing a slit lamp with retro-illumination.
Flourescein can also be used to outline intact microcysts and stain the punctate areas where microcysts have ruptured.

Front 213

Corneal Striae

Back 213

Corneal striae are linear opacities in the cornea. They may also be refered to as striae, folds, wrinkles, striate corneal lines. The terminology is ambiguous.

These are seen as vertically oriented, delicate, translucent lines located at or near the level of Descemet's membrane. Corneal striae are best seen either with retroillumination or with direct illumination.

They are found in up to 50% of soft lens wearers but are very rare in rigid contact lens wearers. The reason for this is not completely understood.

Front 214

Conjunctival and Episcleral Injection

Back 214

Episcleral injection is a nonspecific manifestation of an inflammation of the conjunctiva. It occurs when the conjunctival vessels become red. Contact lens wear can be the cause of episcleral injection in the following circumstances:

The result of allergic or toxic reactions to various contact lens solutions
Infectious conjunctivitis, although this is generally coincidental and is rarely due to contact lens wear
alterations in the integrity of the corneal epithelium which can be caused by direct trauma or by exposure related hypoxia and dessication.

Front 215

Giant Papillary Conjunctivitis

Back 215

GPC is a nonspecific response to a conjunctival insult. It results in the formation of papillae on the palpebral conjunctiva.
A papillae is a small conjunctial elevation. It is seen most frequently in soft contact lens wear and is rarely seen with hard lenses.

Front 216

Corneal Vascularization

Back 216

The invasion of blood vessels into the cornea is known as corneal vascularization. It may occur as the result of epithelial infection, degenerations, exposure to toxins, noninfectious inflammatory conditions, hypoxia, or trauma.

In addition, vascularization may be induced by contact lens wear in the following circumstances:
persistent epithelial hypoxia
recurrent epithelial defects
surgical, traumatic, or other pathological condition for which a contact lens is worn.

Front 217

Keratometer Mire Distortion

Back 217

Irregular astigmatism or apecal displacement may be indicated by distorted keratometry mires.
Contact lens wear has been associated with alterations in corneal topography. These changes can be intentional such as in the case of orthokeratology. Preocular tear film abnormalties can also result in distorted keratometer mires.

Front 218

Corneal Epithelial Staining Patterns

Back 218

The loss of corneal epithelial cells is one of the most common adverse side effects of contact lens wear. Although this can be detected through the use of a slit lamp, the installation of flourescein dye can indicate the precise nature and location of specific corneal epithelial defects. Flourescein acts either by pooling in the area of the defect or by staining the underlying exposed basement membrane of Bowman's layer.

Corneal epithelial damage can result in the discrete loss of a few epithelial cells to deeper craterlike lesions with cell loss to the level of Bowman's membrane. Epithelial damage can be caused either by direct trauma or by defective tear film distribution over the cornea.

Front 219

Epithelial Defects Induced by Direct Trauma

Back 219

1. A poorly edged or damaged lens
2. An excessively flat lens
3. Foreign particles such as dust or cosmetics which lodge beneath the lens.
4. Improper insertion, removal, and reentering techniques
5. Poor cleaning habits
6. Mucus build up generally due to the dry storage of hard lenses.

Front 220

Epithelial Defects Induced by Defective Tear Film Distribution

Back 220

Defective tear film distribution can be due either to abnormalties in the quantity or composition of the tear film or by blinking problems such as a decreased blink rate or "false" blinking. Such conditions can lead to corneal exposure and drying, or to corneal hypoxia under the contact lens or both.

1. Desiccation or drying of the corneal epithelium around the periphery of the lens, especially at the 3 and 9 o'clock. Movement of the lens over these areas can dislodge the compromised epithelial cells.

2. Hypoxia, (oxygen deprivation) under the lens due to inadequate tear flow can lead to the development of microcysts. When these rupture or are abraded, defects will result.

3. Corneal edema resulting from chronic hypoxia can alter the cornea contour and thereby reduce the normal clearance between the cornea and the posterior surface of the lens. Epithelial defects can then result from the lens movement over these areas.

Front 221

The Slit Lamp (General Characteristics)

Back 221

The slit lamp or the biomicroscope is an instrument designed primarily to observe the transparent structures of the human eye under a magnification of from 10 to 50 times.
Its two principle parts include a lamp equipped with an optical system designed to project a slit of light upon the eye, and a stereomicroscope which is mounted horizontally for direct viewing of the patients eye.
The slit lamp may be adjusted to project a variety of light beams. By varying the light beam and the viewing postion, it is possible to improve the view of the various structures of the eye.

Since thed biomicroscope is particularly useful for examining the cornea it plays an especially important role in the fitting of contact lenses. Symptoms of a poor fitting lens can usually be first detected through the use of the slit lamp.

Front 222

Slit Lamp (Diffuse Illumination)

Back 222

A wide beam of light is directed obliquely at the cornea with no attempt to focus the light. It provides a good over all picture of the cornea but no fine details can be seen. It is used primarily for a general survery of the eye.

Uses: The extent of a corneal scar or infiltration can be observed along with the presence of folds or straie in Descemet's membrane. Corneal edema may be seen as a hazy, grey, somewhat granular appearance.

Front 223

Slit Lamp (Direct Focal Illumination)

Back 223

The microscope and the beam of light are focused on the same area. There are three types of direct focal illumination:
1. optic section: used to see all three layers of the cornea. It is possible to determine distortions in the corneal contour and the depth of foreign bodies.
2. parallelepiped: provides a broader view of the anterior and posterior corneal surfaces. It is used to help assess any surface irregularities which may exist and to examine the endothelium. It is often used with flourescein in helping to determine the fit of the contact lens.
3. conical beam: it is the most sensitive method for observing flare or relucency in normal aqueous humor in the anterior chamber. Using high magnification it resembles light penertating fog.

Front 224

Slit Lamp (Indirect Illumination)

Back 224

The observer focuses the microscope on an area immediately adjacent to the illuminated position. It is particularly valuable for studying the iris for pathology.

Front 225

Slit Lamp (Retro Illumination)

Back 225

The light is focused on the deeper structures such as the iris, lens, or retina while the microscope is focused to study the more anterior structures in the reflected light.
Most typically, the light is reflected from the iris in order to study the cornea. It can be useful for the examination of corneal edema and to view blood vessels that have invaded the cornea. It can also be used to study deposits on Descemet's membrane.

Front 226

Slit Lamp (Specular Reflection)

Back 226

The illuminating arm and the microscope are positioned such that the beam of light, when reflected from the corneal surfaces, will pass through one of the oculars of the microscope. At this point the angle of incidence of the light will be equal to the angle of reflection.
It is used for observing elevation and depressions of the anterior surface of the cornea of a soft contact lens. It may also be used to observe lipid or calcium deposits on contact lenses and their general wetting condition.
This form of illumination can also be used to observe the pre-corneal tear film to include mucus and meiobomian secretions.

Front 227

Slit Lamp (Sclerotic Scatter)

Back 227

A broad beam of light is focused a the temporal limbus so it transilluminates through to the nasal limbus. The microscope is then focused sharply on the cornea. Sclerotic scatter and the unaided eye is used to detect the presence of corneal edema which appears as a foggy patch of cotton.

Front 228

Coblat Blue Filter (Slit Lamp)

Back 228

A cobalt blue filter is often used after the instillation of flourescein to observe staining patterns and lens fit.

Front 229

White Filter (slit lamp)

Back 229

A white filter is used to decrease ultraviolet rays and minimally decrease light intensity. It is used primarily for routine examination.

Front 230

Neutral Density Filter (slit lamp)

Back 230

Decreases light intesity by 10%. Used to examine eyelids and conjunctiva. Useful for photophobic patients.

Front 231

Green Filter/ Red Free (slit lamp)

Back 231

Makes red or brown objects blacker. Useful for observing blood vessels.

Front 232

The eyelids play an important role in the fitting and wear of contact lenses for which of the following reasons:

a) they effect the wetting ability of the lens surface
b) they effect the positioning of the lens
c) they are sensitive and generally cause most of the discomfort when a lens is first placed on the eye
d) all of the above

Back 232

d) all of the above

Front 233

Small punctate stains on the corneal epithelium when seen under an ultraviolet light are most likely caused by:

a) foreign bodies
b) loose lens
c) tight lenses
d) apical clearance lenses

Back 233

c) tight lenses

Front 234

After about four hours of wear, your patient complains that his eyes feel "hot". This may indicate:

a) too small of a lens
b) too large of a lens
c) too loose of a lens
d) too tight of a lens

Back 234

d) too tight of a lens

Front 235

Three and nine o'clock staining is generally seen with:

a) soft lenses
b) rigid PMMA lenses
c) gas permeable lenses
d) flourocarbon lenses

Back 235

b) rigid PMMA lenses

Front 236

A rigid gas permeable contact lens is causing a slight stagnation of tears over the corneal apex. One possible lens modification might be:

a) reduce the base curve radius
b) reduce the lens diameter
c) increase the lens diameter
d) fenstrate the lens

Back 236

b) reduce the lens diameter

Front 237

When the fitter observes the occurance of neovascularization, the first course of action should be:

a) return the patient to the prescribing practitioner
b) recommend a different lens material
c) increase the lens diameter
d) truncate the lens

Back 237

a) return the patient to the prescribing practioner

Front 238

The slit lamp illumination most commonly used for detecting corneal edema is:

a) cobalt light
b) direct focal illumination
c) sclerotic scatter and the naked eye
d) conical beam

Back 238

c) sclerotic scatter and the naked eye

Front 239

Limbal peripheral staining may indicate the possibility of:

a) cataracts
b) corneal vascularization
c) a retinal detachment
d) giant papillary conjunctivitis

Back 239

b) corneal vascularization

Front 240

When an adapted contact lens patient manifests significantly increased scleral injection it would indicate:

a) the need for medical attention
b) a normal condition
c) toric lenses may be required in time
d) a condition that will clear up in time

Back 240

a) the need for medical attention

Front 241

During a slit lamp evaluation, a hazzy cornea is an indication of:

a) a well fitting lens
b) a corneal ulceration
c) corneal edema
d) a loose fitting lens

Back 241

c) corneal edema

Front 242

Focusing the beam of the slit lamp directly on the limbus and observing the cornea without the use of the microscope is an excellent way to observe:

a) epithelial erosion
b) the lens cornea relation
c) pathology of the iris
d) diffuse epithelial edema

Back 242

d) diffuse epithelial edema

Front 243

Superficial punctate staining at the corneal apex combined with edema in this region might indicate:
1. a steep fit
2. a flat fit
3. overwearing

a) 1 only
b) 3 only
c) 1 and 2
d) 1, 2, and 3

Back 243

a) a steep fit

Front 244

Corneal staining as observed with a slit lamp may be caused by which of the following:
1. a foreign body
2. poor insertion technique
3. poor edge design

a) 1 only
b) 3 only
c) 1 and 2
d) 1, 2, and 3

Back 244

d) 1, 2, and 3

Front 245

A significant foreign body stain is observed on the cornea during the prefitting evaluation. Which of the following should the fitter do?

a) fit a bandage lens
b) fit a gas perm lens
c) fit a soft lens
d) consult the prescribing practitioner

Back 245

d) consult the prescribing practitioner

Front 246

During a slit lamp evaluation certain areas of the cornea are observed which appear dark, retain their configuration during blinking, and do not stain. These areas most likely represent:

a) dry spots
b) microcystic edema
c) neovascularization
d) a corneal ulceration

Back 246

a) dry spots

Front 247

The average pH of the human tear is:

a) 10
b) 7.8
c) 7.4
d) 6.6

Back 247

c) 7.4

Front 248

A long time successful wearer of gas permeable silicone acrylate lenses presents with superficial punctate keratitis, but complains of no visual problems. The most likely cause is:

a) overwearing
b) protein build up on lens
c) scleral injection
d) GPC

Back 248

b) protein build up on the lens

Front 249

Punctate staining is generally the result of:

a) inadequate tear exchange
b) a poor edge design
c) compression of the lens on the cornea
d) corneal dehydration

Back 249

a) inadequate tear exchange

Front 250

Prolonged corneal edema can result in:

a) photophobia
b) limbal injection
c) excessive spectacle blur
d) all of the above

Back 250

d) all of the above

Front 251

Stippling can result when when there is:

a) inadequate tear exchange
b) too flat of a lens
c) too large of a lens
d) too small of a lens

Back 251

a) inadequate tear exchange

Front 252

An arc shaped stain can be caused by:

a) lens compression on the cornea
b) inadequate tear exchange
c) dellen
d) a poor edge that is not well rounded

Back 252

d) a poor edge that is not well rounded

Front 253

Corneal vascularization is most likely to occur with:

a) gas permeable lenses
b) soft lenses
c) PMMA lenses
d) bandage lenses

Back 253

c) PMMA lenses

Front 254

_____________ is not considered to be a normal adaptive sympton of rigid lenses.

a) photophobia
b) tearing
c) lid sensation
d) punctate staining

Back 254

d) punctate staining

Front 255

Corneal vascularization induced by contact lens wear can be caused by:

1. dellen
2. irregular astigmatism
3. recurring and persistant epithelial hypoxia
4. recurring epithelial defects

a) 1 and 2
b) 1, 2, and 3
c) 2 and 4
d) 3 and 4

Back 255

d) 3 and 4

Front 256

A slit lamp is focused on one of the deeper structures of the eye such as the lens or iris while the microscope focuses on the more anterior structures in the reflected light. This illumination is known as:

a) specular reflection
b) sclerotic scatter
c) direct focal illumination
d) retro illumination

Back 256

d) retro illumination

Front 257

Following the installation of flourescein it is sometimes useful to use the ____________ filter of the slit lamp to observe staining patterns.

a) neutral density
b) green
c) cobalt blue
d) white

Back 257

c) cobalt blue

Front 258

The invasion of new blood vessels into the cornea is known as:

a) deturgence
b) keratitis sclera
c) neovascularization
d) bullous keratopathy

Back 258

c) neovascularization

Front 259

Conjunctiva and episcleral injection can be caused by:

a) toxic reactions to various contact lens solutions
b) infectious conjunctivitis
c) alterations in the integrity of the corneal epithelium caused by direct trauma
d) all of the above

Back 259

d) all of the above

Front 260

When using flourescein to aid in the evaluation of the fit of a rigid lens fit, a special filter must be used with:

a) PMMA
b) Fluorocarbon
c) HEMA
d) Silicone acrylate

Back 260

b) fluorocarbon

Front 261

Presbyopia (Options for Contact Lens Fitting)

Back 261

1. Provide reading glasses to be worn over the contact lenses: While this option generally provides the best vision of all for reading, it is often rejected by patients who complain about having to wear any glasses at all in addition to the contacts.

2. Provide two pairs of contact lenses, one for reading and another for distance: not a practical solution. It would require the patient to change lenses whenever switching the gaze from distance to reading for any period of time.

3. Monovision: popular and successful method. It involves placing a distance lens in the dominiant eye and a near vision lens in the other eye. Most patients will adjust to them in a relatively short time, but there will always be one eye with blurred vision.
Occassionally, a bifocal lens is placed in the nondominant eye to aid with distance vision. Simple and cost effective method.

4. Bifocal contact lenses

Front 262

Bifocal Contact Lenses

Back 262

Two broad categories of design: concentric or target bifocal and the segment bifocal.

1. The concentric, target, or annular bifocal: the distance portion is located in the central portion of the lens while the surrounding optical portion contains the near vision prescription. They can contain a progressive addition or can be a simultaneous bifocal where the reading and the distance portion come into the pupillary area at the same time and the wearer selects which portion to focus through on a subliminal level.

2. The segment bifocal: the segment bifocal can sometimes provide better vision for reading than does the concentric design, however it is a thicker lens and will rest on the lower lid increasing lens awareness.
Because of its design the segment bifocal needs to be stabilized in a vertically oriented position. This is achieved through the use of a prism ballast often combined with truncation.
The reading segment is most often a crescent shape, but can also be a circle of flat top. It can be fused on the back of the lens or ground into the front.
The tangent streak bifocal lens is a fused segment bifocal with a very large reading segment. It is prism ballasted, custom made, and avaliable with variable segment heights and a variable optic zone.

Front 263

Patient Selection for Bifocal Contact Lenses

Back 263

Most Likely to Succeed
1. Those who were successful single vision wearers
2. Those who are highly motivated and who have a highly motivated fitter
3. Those who have an occupational need for bifocal contact lenses

Bifocal Soft Lenses Patient Selection
1. Reading addition should be between +1.00 and +1.75
2. The spherical equivalent addition should be between -4.00 and +2.00 with no more than one diopter of cylinder in the refraction.
3. The patient should understand that visual acuity under all circumstances may not be as good as it would be with spectacles. Small print in dim lighting conditions may still require reading glasses.

Front 264

Astigmatic (Toric) Lenses

Back 264

Toric contact lenses may be indicated when residual astigmatism results in vision which is compromised. Residual astigmatism may result from a toric posterior corneal suface, a toric crystalline lens, or a partially dislocated crystalline lens. Toric lenses may also be required when moderate to high corneal astigmatism results in either mechanical irritation or centration problems with spherical hard lenses.

Toric contact lenses may be classified into the following categories and these are both applicable to both soft and hard lenses.
1. Toric peripheral curves with spherical base curves
a) Spherical front surface
b) Cylindrical front surface

2. Anterior toric, with spherical back surface

3. Posterior toric base curves
a) posterior toric only
b) bitoric

Front 265

Types of Astigmatic Lenses

Back 265

Toric peripheral curve lenses with spherical base curves: These are rarely dispensed in this country, and when they are it is only hard lenses. They are used in cases of low to medium corneal astigmatism when shperical lenses result in inadequate stability. The peripheral curves are shaped to conform to the shape of the cornea contributing to added stability. Trial lenses are required for successful fitting.

Anterior toric with spherical back curves: These are avaliable in both soft and hard lenses. They are typically fit when there is a significant amount, generally more than 0.75D, of uncorrected residual astigmatism. The correcting cylinder is put on the front surface of the lens while the diameter and posterior curves remain the same.

Posterior base curve toric lens: Avaliable in both soft and hard lenses although they are predominately used with hard lenses. They are indicated when a spherical lens does not provide a stable fit and when there is at least 1.50D of corneal astigmatism. They can also be indicated when irritation is experienced due to inadequate clearance of a spherical lens on a corneal cylinder.

A bitoric lens: Needed when the back toric surface results in enough residual astigmatism so that a front surface correcting cylinder is needed. At least 1.50D of corneal astigmatism should be present.

Front 266

Prism Ballast (Stabilization of Toric Contact Lenses)

Back 266

This is one of the most common stabilizing techniques.
A prism of between 1 and 1.50D is ground into the base of the lens. However greater amounts of prism may be needed for patients with particularly tight lids, flat corneas, or oblique axis astigmatism. The lens will tend to rotate so that the base of the prism is oriented inferiorly. The added thickness of the lens along the prism base can reduce oxygen permeability through the portion of the lens resulting in possible hypoxia disturbances in the inferior zone of the cornea.

Front 267

Truncation (Stabilization Technique for Toric Contact Lenses)

Back 267

When a lens is truncated, a portion of it is sectioned off. It is usually 0.50 to 1.5mm on the lower edge of the lens. The amount sectioned off will depend on the size of the lens; larger lenses require greater amounts than smaller lenses. Occassionally the upper edge is sectioned off as well resulting in a double truncated lens. The truncation will serve to stabilize the lens when the lower flat edge comes to lie adjacent to the lower eyelid margin. Truncation is often combined with prism ballast.
When a lens is truncated its diameter is effectively reduced which results in a looser fit. To compensate for this the base curves of truncated lenses are generally made somewhat steeper.

Front 268

Double Slab-off Lenses (Stabilization of Toric Lenses)

Back 268

This technique creates a lens which is thicker along its central body which lies along the palpebral fissure and thinner along the inferior and superior edges which come to lie under the upper and lower lids. This technique is comfortable since there is no lid impact along the inferior surface. However it does not offer as much lens stability as the truncated or posterior toric techniques. Double slab-off lenses are often combined with a prism ballast to help prevent rotation.

Front 269

Posterior Toric Lenses (Stabilization Technique for Toric Lenses)

Back 269

A back toric surface can be used as a lens stabilizing technique. When the shape of the posterior contact lens surface closely parallels that of the cornea lens rotation can be minimized.

Front 270

Aspheric Lens Surface (Stabilization Technique for Toric Contact Lenses)

Back 270

An aspheric surface can aid in lens-axis stabilization by adding drag to the motion of the lens. It is generally used in combination with truncation or prism ballast since it is only minimally effective by itself.

Front 271

Toric Lens Rotation

Back 271

Because it is necessary to inhibit lens rotation, toric lenses will typically come with reference markings so the fitter can determine how the lens is oriented on the cornea. These markings may be circles or lines located at the six-o-clock or three and nine-o-clock meridians.

The expression LARS stands for left add, right subtract. If the lens is rotated to the fitters left, the appropriate number of degrees is added to the prescribed axis. If it is rotated to the right the appropriate number of degrees is subtracted.

Lens rotation can measured using a slit lamp equipped with a protractor. The use of trial lenses is especially important when fitting toric lenses.

Front 272

Aphakia (Patient Selection)

Back 272

Certain guidelines apply for the selection of potential aphakic lens patients. They must be able to handle the lens either on a daily or weekly basis and possess the ability to properly care for the lenses. Like any contact lens candidate there needs to be sufficient tear film as well as an abscence of any serious corneal disease.

Front 273

Aphakia (Types of Rigid Aphakic Lenses)

Back 273

There are basically two types of rigid aphakic lenses. These include the minus carrier lenticular lens and the single-cut lens.
The conventional lenticular lens is rarely used since it tends to ride low when the upper lid collides with the steep curve of the anterior optic zone, pushing it downward. This same occurance can also cause lid irritation.

Front 274

Minus Carrier Lens (Aphakia)

Back 274

The minus carrier lens is well supported by the upper lid and can be held in position about 1mm above the corneal center. It is also much thinner than the convetional lenticular lens further reducing the tendency for it to drop over the limbus.
The optic zone of the minus carrier lenticular lens generally is relatively small, about 7.0mm in diameter. The smaller zone results in both reduced center thickness and lighter weight.

Front 275

The Single Cut Lens (Aphakia)

Back 275

The single cut rigid aphakic contact lens is sometimes prescribed when one or more of the following conditions are met: small palpebral apertures, relatively steep corneas (over 45.00D), or when other lens designs tend to ride low.
Since these lenses are smaller than a lenticular design the edges are made thinner, making them more comfortable. Although smaller, the size of the optic zone of the single cut lens is quite comparable to that of the lenticular.
One advantage to the single cut lens design is the abscence of a sharp juncture between the two curves on the front surface thus eliminating the annoying lid bump.
A disadvantage to the single cut lens is the difficulty encountered in removing this small steep lens from the cornea, especially for the elderly.

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Aphakic Soft Lenses

Back 276

Aphakic lenses are the thickest lenses used. In the case of the high myope of say -12.00D, the thinnest portion of the lens lies over the visual axis. A +12.00D aphake, however, finds the thickest portion of the lens over the corneal cap and visual axis. Any corneal edema resulting from the use of soft lenses for aphakia, therefore is found over the most critical part of that structure. Even when highly gas permeable lenses are used, the permeability at aphakic levels of lens thickness may still be relatively low. An aphakic soft lens can cause a 4 to 8% increase in corneal thickness.

Aphakic soft lenses can be excpected to last from about six months to one year. Their life expectancy can be shortened by any of the following:
Protein or other deposits which may interfere with clarity of vision.
Tearing or splitting of the lens caused by a fingernail or perhaps poor placement in its case.
Loss due to the difficulty of the aphakic patient in seeing or feeling the lens, especially when it is stored in a liquid medium.

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Aphakic Soft Lenses (General Difficulties)

Back 277

Any contact lens rigid or soft must be handled. This can be a problem for the elderly patient with arthritis, a head or finger tremor, or poor central visual acuity resulting from macular degeneration. Further, elderly patients often experience difficulty coping with lens insertions and maintaing adequate supplies of the necessary solutions.
Those who live alone may fear one day being unable to remove their lenses. Bilateral aphakes cant see to find their lenses unless they use a special accessory device. For these and other reasons contact lenses for the correction of aphakia are being used less frequently. Due to improved surgical techniques and materials, intraocular lens implants are becoming the treatment of choice for the great majority of cataract patients.

Front 278

Keratoconus

Back 278

A degenerative hereditary condition of the cornea. It results in a progressive thinning of the central or paracentral area of the cornea and is accompanied by irregular astigmatism. In more advanced cases the cornea can form a buldge or a cone which is often located near or just below its center. In other cases a diffuse thinning of the cornea can result in a sagging cone otherwise known as Keratoglobus.

Front 279

Advanced Keratoconus

Back 279

Advanced keratoconus can be divided into two principal clinical categories: the round or nipple shapped cone and the oval or sagging cone.
The round cone is the most common type and typically lies in the lower nasal quadrant. The sagging cone is usually longer and steeper than the round cone. It sags in the inferotemporal quadrant with an average reading of 68D. The round cone is rarely greater than 65D and it responds more favorably to contact lens fitting.

Front 280

Keratoconus (Treatment With Contact Lenses)

Back 280

Keratoconus may be successfully treated with contact lenses. The purpose of the lens is to cover the irregular astigmatism created by the distorted anterior surface of the cornea.
The tear layer found between the back surface of the contact lens and the front surface of the cornea serves to fill in the corneal irregularities thereby providing a smooth optical surface.
Rigid lenses are far more effective at accomplishing this purpose than are soft lenses. Contact lenses do not retard the progression of the disease nor do they provide a cure, although the patient may experience long periods of natural remission. Successful fitting requires a combination of patience, diplomacy, and a great deal of skill. Spectacles are only helpful in early, mild cases.

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Single Cut Lenses (Keratoconus)

Back 281

In the ideal fit, these lenses will touch the apical cone lightly and come to rest on the peripheral cornea in an area where there is little or no thinning. Lenses fit excessively flat may cause corneal abrasions. Lenses fit too steep to cause even minimal apecal clearance will result in the pooling of tears around the periphery of the cone. The pooling of tears can result in discomfort, hazing and bubble formation.

Front 282

Soper Keratoconus Diagnostic Fitting Set

Back 282

These lenses are designed with a steep base curve to accomodate the steep central cone area with a much flatter peripheral curve to rest on the surrounding cornea. It is essential to use a trial set containing base curves of 48 to 60D when fitting these lenses. The lens diameters range from 7.5 to 9.5mm.
A good fitting lens would show the following: apical clearance with circulation of tears between the apex of the cornea and the back of the lens, good centration, and some movement of the lens with blinking.

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Thin Lens (Keratoconus)

Back 283

These are sometimes referred to as Dura-T-Lenses. The key element in their design is that they are made thinner with a center thickness of about 0.8mm. The reduced mass also reduces the lens weight by about 30% and assists in centration and patient tolerance.

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Soft Lenses (Keratoconus)

Back 284

They are useful for the patient who can not tolerate rigid lenses. They are fit with a relatively flat base curve 8.1 to 8.4mm and a fairly large diameter 13 to 14mm in order to provide lens stability.
While soft lenses dont normally mask astigmatism, they have been shown to reduce a significant amount so that overcorrection with spectacle lenses become effective.

Front 285

Piggyback Lenses (Keratoconus)

Back 285

These are used when the patient cannot tolerate rigid lenses and when the use of auxillary spectacles needs to be avoided. A soft lens of about 14mm in diameter is placed on the cornea. A rigid lens is placed over it which may ride freely or be placed in a depression in the soft lens designed to hold the rigid lens in place. The diameter of the rigid lens usually ranges from 8.5 to 9.5mm.

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Extending the Range of the Keratometer

Back 286

The range of the keratometer may be extended in the steeper range by placing a +1.25D lens over the aperture. It may be extended in the flatter range by placing a -1.00 lens over the aperature.

Front 287

Contact lenses for the correction of aphakia have certain advantages over spectacle lenses. These include:

a) less peripheral aberration
b) less magnification
c) increased visual field
d) all of the above

Back 287

d) all of the above

Front 288

A conical shaped cornea can best be fit with contact lenses through the use of:

a) trial lenses
b) keratometer readings
c) eye impressions
d) topogometer readings

Back 288

a) trial lenses

Front 289

Prism ballast lenses can be useful for:

a) helping to reduce lens rotation
b) for cylindrical lenses
c) for some bifocals
d) all of the above

Back 289

d) all of the above

Front 290

Bitoric lenses are prescribed:

a) only when there is a small amount of corneal astigmatism and no residual astigmatism
b) when there is no corneal astigmatism
c) only for bifocal contact lenses
d) when there is at least 1.50D of corneal astigmatism accompanied by a significant amount of residual astigmatism

Back 290

d) when there is at least 1.50D of corneal astigmatism accompanied by a significant amount of residual astigmatism

Front 291

K: 41.50 @ 90 / 42.75 @ 180
This K reading indicates:

a) astigmatism with the rule
b) astigmatism against the rule
c) oblique astigmatism
d) residual astigmatism only

Back 291

b) astigmatism against the rule

Front 292

Rx: -4.50 +2.50 x 95
K: 44.75 @ 90 / 45.00 @ 180
This information would most likely indicate the fitting of which of the following?

a) spherical contact lens
b) bitoric contact lenses
c) front toric contact lenses
d) monovision

Back 292

c) front toric contact lenses

Front 293

Early stages of keratoconus may be detected through the use of the ______________.

a) slit lamp
b) radiuscope
c) keratometer
d) retinoscope

Back 293

c) keratometer

Front 294

The hyperflange lens design is useful in fitting which of the following?

a) high minus lenses
b) low minus lenses
c) high plus lenses
d) low plus lenses

Back 294

a) high minus lenses

Front 295

A patient who has been diagnosed as having keratoconus may present which of the following during a slit lamp examination?

1. thinning of the corneal apex
2. thinning of the pupil
3. thickening of the sclera

a) 1 only
b) 1 and 2
c) 2 only
d) 1, 2, and 3

Back 295

a) 1 only

Front 296

a contact lens is ordered with the following specifications:
K: 42.50 @ 180 / 43.50 @ 90
Rx: -11.25 -0.75 x 180

Which of the following designs should be considered for this lens?
1. myoflange
2. prism
3. hyperflange

a) 3 only
b) 2 only
c) 1 only
d) 1, 2, and 3

Back 296

a) 3 only

Front 297

When fitting the keratoconus patient, which of the following lens styles could be considered?

1. aspheric
2. Soper
3. tangent streak
4. front toric with prism

a) 1 and 2
b) 2 and 3
c) 3 and 4
d) 1, 2, and 4

Back 297

a) 1 and 2

Front 298

Certain styles of bifocal lenses may rotate without vision impairment. One example of these would be:

a) executive
b) fused crescent
c) tangent streak
d) annular

Back 298

d) annular

Front 299

When fitting a keratoconus patient, the lens should:

a) ride low
b) ride high
c) flatten the apex
d) align the apex

Back 299

d) align the apex

Front 300

Myoflange lenses for high plus prescriptions have the following advantages:
1. reduced center thickness
2. increased optical zone
3. reduced weight

a) 1 only
b) 1 and 3
c) 2 and 3
d) 1, 2, and 3

Back 300

b) 1 and 3

Front 301

How well a soft toric lens performs on the cornea depends on several factors. These would include:

1. tightness of the lid
2. shape of the cornea
3. where the lids are positioned
4. lid shape

a) 1 only
b) 1 and 3
c) 2 and 3
d) 1, 2, 3, and 4

Back 301

d) 1, 2, 3, and 4

Front 302

A spherical rigid gas permeable lens fit on the cornea with a signifcant amount of with the rule astigmatism will show touch:

a) along the verticle meridian
b) along the horizontal meridian
c) along the oblique meridian
d) along the residual meridian

Back 302

b) along the horizontal meridian

Front 303

It is possible to extend the range of a keratometer to 61.00D through the use of an auxillary trial lens with a power of:

a) -1.25
b) +1.25
c) -1.00
d) +1.00

Back 303

b) +1.25

Front 304

Single cut aphakic lenses can be well suited for patients with:

a) small aperatures and flat corneas
b) large aperatures and flat corneas
c) small aperatures and flat corneas
d) small aperatures and steep corneas

Back 304

d) small aperatures and steep corneas

Front 305

K: 40.25 x 180/ 41.00 x 90
Rx: +12.50

a good lens design for this aphakic patient who also shows large palpebral fissures and flaccid lower lids would be:

a) back toric
b) myoflange lenticular
c) hyperflange
d) single cut

Back 305

b) myoflange lenticular

Front 306

When the power of a bifocal lens gradually changes from the central area of the lens to the periphery it is called:

a) an aspherical lens
b) a tangent streak lens
c) a crescent lens
d) a monocentric lens

Back 306

a) an aspherical lens

Front 307

It is possible to inhibit the rotation of a rigid bifocal contact lens by:

a) truncating the lens
b) using a prism ballast
c) a double slab off technique
d) all of the above

Back 307

d) all of the above

Front 308

Corneal sensitivity is generally reduced:

a) after cataract surgery
b) in cases of advanced presbyopes
c) in young children
d) when adapting to rigid contact lenses

Back 308

a) after cataract surgery

Front 309

In managing the keratoconus patient, which piece of information is of little value?

a) shape of the cone
b) diameter of the cone
c) size of the cone
d) keratometry axis

Back 309

d) keratometry axis

Front 310

Residual astigmatism can be corrected through the use of:

a) spherical soft lenses
b) spherical rigid lenses
c) toric lenses
d) small diameter lenses

Back 310

c) toric lenses

Front 311

Presbyopia may be corrected through the use of single vision contact lenses by placing the distance vision Rx in the dominant eye and near vision Rx in the other eye. This is called:

a) monovision
b) bivision
c) concentric lens fit

Back 311

a) monovision

Front 312

When therapeutic soft lenses are prescribed, they are sometimes fit so that there is minimal movement. A lens to be fit in this manner would be indicated by:

a) keratoconus
b) striate keratopathy
c) bilateral aphakia
d) recurrent epithelial erosion

Back 312

d) recurrent epithelial erosion

Front 313

Rx: -7.00 -2.75 x 170
K: 43.00/43.00

When using a trial lens and slit lamp to evaluate the fit of a toric soft lens you notice that the reference marking is positioned at 7 o'clock. What is the cylinder axis of the lens to be ordered?

a) 170
b) 180
c) 010
d) 020

Back 313

d) 020

Front 314

Possible In-Office Lens Modifications for Rigid Contact Lenses

Back 314

1. Blend transition or junction zones
2. Reduce optic zone diameter
3. Reduce overall lens diameter
4. Flatten intermediate curves
5. Add minus power
6. Add plus power
7. Remove scratches
8. Polish and refinish lens edge
9. Adjust peripheral curves
10. Identify the lens
11. Fenstrate the lens
12. Flatten the base curve

Front 315

Polishing Compunds (Office Modifications)

Back 315

Lenses can be polished using a polishing compound which is a mild abrasive agent. These agents are known as Silvo or Xpal and are mixed with either oil or water.
Since Silvo is a coarser abrasive, it tends to scratch the relatively soft gas permeable materials, therefore the finner compund Xpal is generally more desirable.
Also, there are several commercially avaliable polishing solutions which are specifically designed for gas permeable lenses such as Alox PG, or Sil O2 care.

Front 316

Blending Transition of Junction Zones (Office Modification)

Back 316

The junction zone between two curves should be a smooth transition. If not, it can interfere with tear exchange under the lens.
If the junction zone is particularly sharp, it may irritate the cornea in a manner similar to a sharp lens edge. A transition zone may be blended by using a tool in which the radius of curvature is half way between that of the two curves being blended.
The junction may occur either between the CPC and IPC or the IPC and PPC.

Front 317

Reducing the Optic Zone Diameter (Office Modification)

Back 317

Doing this will loosen the fit of the lens since the size and curvature of this zone will help determine how tight or loose the fit will be.
This may be accomplished either by increasing the width of the PPC or IPC, or by adding a blend or increasing the width of the blended area.

Front 318

Reducing the Overall Lens Diameter (Office Modification)

Back 318

This adjustment will also have the effect of loosening the fit of the lens. It may be accomplished either through the use of a razor blade, an emery board, or by employing a cone shaped stone.

Front 319

Flattening the Intermediate Curves (Office Modification)

Back 319

This is accomplished by resurfacing the existing intermediate curve with a felt-covered tool of a flatter radius of curvature.

Front 320

Adding Minus Power (Office Modification)

Back 320

Up to one diopter of minus power may be added to a lens. It is accomplished with a tool covered either with a piece of velvateen or sponge.

Front 321

Adding Plus Power (Office Modification)

Back 321

Up to one diopter of plus power may be added to a rigid contact lens. The technique is similar to that used for adding minus power.

Front 322

Removing Scratches (Office Modification)

Back 322

It is possible to remove scratches from both front and back surfaces of a rigid gas permeable or PMMA contact lens. However care must be taken not to alter the power of the lens in the process.

Front 323

Polishing and Refinishing the Lens Edge (Office Modification)

Back 323

Several techniques may be used for this purpose. The most widely used tool is a felt disc.

Front 324

Adjusting Peripheral Curves (Office Modification)

Back 324

Peripheral curves may be flattened, blended, or made wider. This is generally achieved through the use of a diamond impregnated tool of the correct radius of curvature.

Front 325

Flattening the Base Curve (Office Modification)

Back 325

The base curve of a lens may be flattened by about 0.50D. This is not a frequently performed in office modification.

Front 326

Identifying the Lens (Office Modification)

Back 326

In order to more easily distinguish the right from the left lens the right lens often contains an identification marking such as a red dot.
The marking can be applied through the use of one of several avaliable in-office techniques.

Front 327

Fenstrating the Lens (Office Modification)

Back 327

The drilling of one or more holes through a rigid lens is known as fenstrating and there are modification units designed specifically for this purpose.
Fenstration has the effect of loosening the fit of a lens. It does not significantly increase the flow of oxygen through the lens as it is sometimes believed.

Front 328

Radiuscope

Back 328

The radiuscope is designed to measure the radius of curvature of the anterior and posterior surfaces of rigid lenses. All the commonly avaliable radiuscopes operate using procedures similar to the following:

1. A drop of water is placed on the lens mount upon which a contact lens is floated convex side down.
2. A spot of light is centered im the middle of the lend and the body of the microscope is raised as high as it will go.
3. The microscope is then focused downward until a spoke pattern, the first of three images, comes clearly into view. This is called the aerial image and represents the reflection from the posterior surface of the lens. Once the aerial image becomes sharply focused a pointer is set to zero on the scale.
4. Continue to move the body of the microscope downward. On the way to its final location, an image of the bulb filament will come into view. Continue beyond this image.
5. Eventually, another spoke pattern will come into focus. This represents the level of the lens surface, so it is possible to observe surface details at this point. Focus this 3rd image as sharply as possible. The reading on the scale now represents the radius of curvature of the lens surface in millimeters.
6. It is generally advisable to double check the final reading. This can be accomplished by focusing the microscope all the way up to the original aerial image. At this point the pointer should once again be on 0. If not, reset it at zero and repeat the entire process.