Cl2 Midterm

Front 1

Corneal curvature: steep corneal curvature require?

Back 1

smaller lenses

Front 2

Corneal curvature: flat cornea requires?

Back 2

a larger lense

Front 3

Aligned on K, ie cornea is 45.00

Back 3

base curve is the same as the flat k of the cornea, base curve is 45.00

Front 4

Steep fit, ie cornea is 45.00

Back 4

base curve is steeper than flat k, base curve is 45.50

Front 5

Flatter fit, ie cornea is 45.00

Back 5

base curve is flatter than flat k, base curve is 44.50

Front 6

In determining final power there is 3 things you have to take into account

Back 6

1. patients rx
2. effectivity if the power is 4.00 or over in any meridian
3. Tear lens

Front 7

Tear lens

Back 7

the tear filled gap created by the difference between the base curve and the corneal curve.

Front 8

SAM

Back 8

Steep add minus, there is a plus tear lens, so you need to add minus to cover it.

Front 9

FAP

Back 9

Flat add plus, there is a minus tear lens so you need to add plus to cover it.

Front 10

Center thickness

Back 10

thickness of the lens, minus lenses will be thinner in the middle than plus lenses. the higher the minus the thinner the center.

Front 11

Edge thickness

Back 11

0.08-0.12, a good thin edge adds comfort, the thicker the lens the less blinking which then leads to 3 and 9 o'clock staining.

Front 12

Axial edge lift

Back 12

the vertical distance from the lens edge to the extension of the base curve.

Front 13

Radial edge lift

Back 13

the extension of the lens edge perpendicular to the extension of the base curve, always about 80% of axial edge lift.

Front 14

edge clearance

Back 14

how much lift the lens has against the peripheral cornea. What you see with fluorescein pattern.

Front 15

If edge lift is too great you can

Back 15

steepen the peripheral curve radius, or narrow the peripheral curve width.

Front 16

The three basic RGP lens designs

Back 16

1. interpalpebral
2. Basic tri curve/tetra curve
3. korb or lid attachment design

Front 17

Interpalpebral design

Back 17

original design, smaller lenses 8.0-8.6mm

Front 18

Basic tri-curve/tetra curve design

Back 18

everyday rgp design. usually fits under superior lid. not a lid attached design but can happen. dia 9.2-9.4mm, optic zones usually 7.7-8.2mm

Front 19

Korb or lid attachment design

Back 19

anterior front surface of periphery of lens attaches to the lid and moves with it.

Front 20

Selecting a diameter will depend on:

Back 20

pupil size, corneal curvature (flat corneas get larger lenses), palpebral aperature size

Front 21

lens adherence =

Back 21

lens adherence = optic zone diameter * radius of base curve. Increasing SAG increases adherence.

Front 22

If diameter increases and the BS remains constant?

Back 22

SAG increases, and lens adherence increases as well.

Lens adherence(SAG) = optic zone diameter * radius of base curve.

Front 23

If sagitta increases and the diameter remains constant?

Back 23

the BC must steepen.

Lens adherence(SAG) = optic zone diameter * radius of base curve.

Front 24

Eccentricity value

Back 24

how the cornea or CL flattens as you go out towards the periphery. Avg is 0.55, so 0.6 means the cornea flattens faster then normal, and 0.40 means the cornea flattens slower thena normal.

Front 25

base curve/optic zone interrelationship, in order to maintain a constant SAG.

if base curve is flattened by 0.25D

Back 25

then optic zone must be increased by 0.5.

Lens adherence(SAG) = optic zone diameter * radius of base curve.

Front 26

base curve/optic zone interrelationship, in order to maintain a constant SAG.

if base curve if steepened by 0.25D

Back 26

then optic zone must be decreased by 0.5mm

Lens adherence(SAG) = optic zone diameter * radius of base curve.

Front 27

Tri curve lens radius if base curve is 7.50mm

Back 27

secondary curve radius = 1.0 to 1.5mm flatter = 8.50mm
peripheral curve radius = 1.5 to 2.00mm flatter than SCR = 10.0mm or 10.5mm

Front 28

Peripheral curve widths, overall diameter =?

Back 28

overall diameter = optic zone + 2(secondary curve width) + 2(peripheral curve width)

Front 29

Tetra curve lens peripheral curve system.
secondary curve radius SCR = ?
Tertiary curve radius TCR =?
Peripheral curve radius PCR =?

Back 29

SCR = BC + 0.8mm
TCR = SCR + 1.0mm
PCR = TCR + 1.4mm

Front 30

Tetra-curve widths
SCW = ?
TCW = ?
PCW = ?

Back 30

SCW = 0.3mm
TCW = 0.2mm
PCW = 0.2mm

Front 31

Center Thickness for a minus lens?

Back 31

center thickness = constant + ([BVP]/100)

Front 32

Center thickness for a plus lens?

Back 32

center thickness = constant + (2[BVP]/100)

Front 33

pros and cons of thin lenses

Back 33

pros:
more comfortable
more oxygen transmissible
good centration
cons:
more fragile
more flexure
more warpage
fragile edges

Front 34

most important consideration when choosing a lens

Back 34

patient's pupil size, because if pupil is bigger than optic zone flare might become and issue.

Front 35

RGP Panofocal

Back 35

front aspheric, doesn't correct residual astigmatism but it reduces aberrations to clear the image. cost more but work about 80% of the time. use panofocal when residual astigmatism is about 1.25d or less.

Front 36

Movement is important because

Back 36

1. tear exchange
2. flushing debris away
3. wetting the cornea
4. minimizing pressure on ocular tissues.

Front 37

if lens has excessive movement what can you do?

Back 37

1. make sure patient is adapted to the lens, movement could be due to excessive tearing.
2. make the BC steeper
3. change the diameter, go smaller to give it less lid grab.
4. Taper the edges to create less lid grab.
5. change the lens thickness, going thinner will slow lens movement.

Front 38

If lens movement is inadequate

Back 38

1. Flatten the bc, makes the lens looser
2. go to a larger diameter to increase lid grab and oz.
3. change edge design, last resort.

Front 39

If lens is too low

Back 39

try a larger diameter lens with a larger optic zone and flatter base curve to get more superior lid grab

Front 40

if lens is too high

Back 40

try a smaller diameter lens with a steeper base curve or taper the edge to make the lid grab less.

Front 41

binding?

Back 41

lens is sucked onto the eye, patient maybe comfortable, but bad situation physiologically as it can harm the cornea.

Front 42

Fluorescein pattern

Back 42

assessing the relationship between the back of the lens and the front of the cornea including the tear lens

Front 43

static fluorescein pattern

Back 43

done without lids in play

Front 44

dynamic fluorescein pattern

Back 44

done with lids in play

Front 45

3 areas to observe while doing a fluorescein pattern

Back 45

1. central
2. para-central
3. peripheral or edge

Front 46

WTR fluorescein pattern

Back 46

Dark H pattern

Front 47

ATR fluorescein pattern

Back 47

I pattern

Front 48

common sources of error on fluorescein patterns

Back 48

call mat up
Corneal topography
Astigmatism
Lids and lid action
Lens construction
Movement
Amount of fluorescein used
Tearing
UV source
Position

Front 49

If you increase Optic zone diameter you must be sure to...

Back 49

flatten the base curve to maintain the same sagittal fitting relationship.

lens adherence(sag) = optic zone diameter * radius of base curve

Front 50

If you decrease the optic zone diameter you must

Back 50

steepen the base curve.

lens adherence(sag) = optic zone diameter * radius of base curve.

Front 51

Widening or flattening the peripheral curve

Back 51

more peripheral clearance will occur.

Front 52

Decreasing the optic zone diameter

Back 52

loosens the fitting relationship

Front 53

Axial edge lift

Back 53

vertical distance from the lens edge to the extension of the base curve of the lens, nothing to do with the cornea.

It is the measure of the linear distance between the edge of the CL and the projected trajectory of the BC of the lens. Usually you want this to be 0.10mm. Too high of an AEL will give you excessive clearance and you can get 3 and 9 o clock staining.

Front 54

Radial edge lift

Back 54

linear distance between the edge of the cl perpendicular to the trajectory of the base curve. usually 0.08mm. Doesn't take cornea into concideration.

Front 55

Edge clearance

Back 55

the actual amount of lift of the lens off the cornea. The distance from the lens edge to the cornea measured perpendicular to the cornea. Should be less than the axial edge lift. This takes into account the cornea. This is what you're looking at when you do a fluorescein pattern.

Front 56

increasing the optic zone diameter

Back 56

the peripheral curve width decreases and the axial edge lift and edge clearance will also decrease, will result in a tighter fit.

Front 57

greater axial edge lift on an RGP may cause more

Back 57

3 and 9 o'clock staining due to the lid not moving over the lens property.

Front 58

Aspheric lenses

Back 58

ellipsoid, they parallel or simulate the flattening of the cornea better than regular spherical lenses. Broader contact zone. No worry about blending, and reduces flare.

Front 59

Most important aspect of lens design when determining comfort

Back 59

edge design, edge should be tapered and rolled. Want to ensure that the apex of the edge to be in the rear 1/3 of the lens and rolled. ideally 0.10mm

Front 60

Construction of the Korb lens

Back 60

1. thin to minimize mass and increase oxygen transmission.
2. larger lenses, so more of the lens can get under the lid
3. flatter fitting, 0.25-0.50 flatter than k, helps facilitate lift, ensures higher positioning.

Front 61

Optimal diameter of a korb lens

Back 61

9.5 mm diameter with a 8.4 mm optic zone

Front 62

to raise a low riding lens

Back 62

use a korb lens or a minus lenticular

Front 63

minus carrier lenticular design

Back 63

makes the edge thicker making it easier to hook onto the upper lid.

Front 64

Lenticular flange

Back 64

front carrier radius or curvature is cut or lathed on to the edge of the lens

Front 65

Optic zone or front bowl of a lecticular

Back 65

central optical portion of the lens.

Front 66

The minus carrier radius or flange radius is made...

Back 66

1.0-3.0mm flatter than the base curve radius. The flatter the flange radius, the thicker the edge, the higher the lens rides and less stagnant it becomes.

Front 67

if the carrier radius is steeper in curvature than the central front radius of the lens

Back 67

then the lenticular is a plus edge lenticular.

Front 68

for more lift of the lens you would use a

Back 68

smaller bowl diameter, this allows the flange to be larger, allowing more plastic to get under the lid. The flange should ideally be 0.5-0.6mm.

Front 69

Junctional thickness

Back 69

determined where the front bowl meets the carrier. For plus lenses it is often the thinnest part of the lens, can break if too thin. Should not be thinner than 0.13-0.15mm or breakage can occur.

Front 70

Tapering for high minuses
medium tapers for power?
heavier tapering for power?
CN bevel for?
plus lens lenticulars for?

Back 70

Tapering should be considered for -4.00 - -6.00 D
Medium tapers for -4.00 to -5.00D
Heavy tapers for -5.00D to -6.00 D
CN bevel for -6.00D to -8.00D
plus lens lenticulars for > -8.00D

Front 71

Albinism custom lenses help

Back 71

CL decreases searching nystagmus, a light tint can also help photophobia.

Front 72

X-chrom lens changes...
transmits?
always worn on?

Back 72

color perception for anomalous trichromats.
590-700
non-dominant eye.
enhances colors and depth perception, it oes not cure color vision defects. Only 20% of patients who try the lens actually order it even if it works. Lens it not good in dim illumination.

Front 73

Custom lenses for arcus senilis

Back 73

when patients think that it looks like cancer. cosmetic by nature.

Front 74

Medical uses of CL's

Back 74

1. band keratopathy
2. corneal abrasion
3. bullous keratopathy
4. herpetic lesion

Front 75

Sympathetic nervous system, high amount of stress

Back 75

patient wasn't sleeping, so excessive stimulation was causing both his eye to be dilated at all times. Used an opaque lens to mask the dialation

Front 76

Anisocoria

Back 76

fit both eyes with stock lenses, easier than fitting one eye with a custom lens that would match the other natural eye.

Front 77

Coloboma

Back 77

use opaque cl to cover coloboma.

Front 78

3 and 9 o'clock staining

Back 78

very common, almost a norm in RGP wearers.
Due to
1. thick edge
2. inferior positioning
3. irregular tear film
4. excessive edge lift, 1.0 is optimal, higher may lead to more incidence of staining

Front 79

Vascularized Limbal Keratitis Stage I

Back 79

step beyond 3-9 o clock staining. heaping of corneal of limbal epithelium peripherally. This is due to insufficient edge lift.

Front 80

Lens adhesion

Back 80

seen in new extended wear RGP's. Happens during sleep, lens sits inferior temporal and you get an indention ring. Sulcus, compression ring, indention in the epithelium from RGP.

Front 81

Corneal dimpling

Back 81

depressions in the cornea due to CO2 bubbles under a tight zone. Looks like staining but not actually staining, epithelium is not broken, just more pooling in the depression.

Front 82

Epithelial microcysts

Back 82

wearing lenses too long, hypoxia. patient is in excruciating pain. during the day the cornea develops vesicles in the deep epithelium. over night these vesicles come to the surface burst and release nerve ending causing pain. Use bandage CL focus night and day silicone hydrogel.

Front 83

CCC central corneal clouding

Back 83

epithelial edema, typically in the area of the optic zone. gray haze. not adequate oxygenation.

Front 84

Edematous corneal formation ECF

Back 84

deeper more severe edema. more intense and longer lasting. resembles arborized tree branches, sort of resembles herpetic lesions. can last for weeks or even months. due to long term oxygen deprivation, will not stain because no breaks in epithelium. gradually wean the wearing schedule over a few weeks.

Front 85

corneal warpage syndrome

Back 85

avoid refitting with soft contact lenes. do not tell the patient to stop wearing PMMA lenses for 3 days before the exam.

Front 86

Rengsorff curves

Back 86

describes the change in corneal curvature and refraction after discontinuation of PMMA lens wear. Cornea gets much flatter in the days following discontinuation and then gradually goes back to normal.

Front 87

corneal topography mathematical method

Back 87

favored by visual scientists, an ellipse is closest model for optical portion of the cornea.

Front 88

Photokeratoscopy, corneal topography

Back 88

target or placido rings projected onto cornea and photographed with telecentric optical system. mail the picture to a team of people to calculate and analyze the k, take ~6 weeks to get results back

Front 89

Videokeratoscopy, corneal topography

Back 89

photographic camera replaced with video camera, analysis done in seconds and much more accurate.

Front 90

Topographical maps, corneal topography

Back 90

derived from radius measured at several thousand corneal positions.

Front 91

cataract surgery can leave the cornea

Back 91

with reduced sensitivity and can make patient unaware of corneal ulcer

Front 92

Aphakia patients have a huge problems with contact lenses in that they?

Back 92

tend to lose them, insurance will only cover the first pair after the surgery. Expect an aphakic to go through at least 4 lenses the first year alone.

Front 93

When to fit aphakes with CL's

Back 93

when you start obtaining reliable and repeatable refractions and k readings, indicating that the cornea has settled.

Front 94

welsh lens

Back 94

thin lens, fit steep and smaller to help and hold it to the eye. But it makes it hard to remove from a patient that has flaccid lids. Max thickness 0.35mm with a knife edge.

Front 95

Lenticular carriers in aphakia.

Back 95

better option.
dealing with a minus edge lenticular carrier lens.

Front 96

Using glasses over contact lenses...

Back 96

1. over plus aphakic by 2-3D in Cl.
2. over plussed eye has increased mag, now compensate by putting 2-3d minus at the spectacle plane, the net affect here is minification, making the net magnification closer to that of the non-aphakic eye.
3. Opposite done to the normal eye, over minus then give plus at the spectacle plane to give a net magnification effect.

Front 97

Little aphakes, congenital aphakes

Back 97

age 0 to 1 years old, too early to consider an IOL. But must do something before 6 weeks of development to allow proper development of visual system.

Front 98

Rx range of little aphakes

Back 98

range from 28-32d. tend to drop about 10d after the first year, due to the rapid growth of the eyeball. this is why an iol early is not a good option.

Front 99

k readings of little aphakes

Back 99

k readings will flatten over time, 40-60% over the first year.

Front 100

Monocular cataracts should be removed within?

Back 100

the first few days, this improves the chances that the child will not have amblyopia.

Front 101

Binocular cataracts should be removed within?

Back 101

the first few months.

Front 102

B&L lens used for congenital aphakes that B&L makes nearly no money on.

Back 102

Silsoft, primarily for children, DK 340. Always overplus a child because their world is within arm's length. This lens attracts lipids, must use miraflow cleaner.

Front 103

Why must lenses move? even if they have a dk of 340?

Back 103

1. pumps oxygen
2. pumps waste
3. wets cornea
4. without waste removal or corneal wetting the epithelium will break down and the eye can get infected.

Front 104

IATS: Infant aphakic treatment study

Back 104

examines aphakic infants treated with IOL's versus no IOL's. Critical time is 6 weeks for babies with visual limitations, if intervention is needed do it before that time.

Front 105

Axial topography format

Back 105

data from points along any orneal meridian are always referenced to a normal axis running perpendicularly to the central cornea. may be of greater value in contact lens fitting, as there is more averaging of data over a larger area.

Front 106

Tangential topography format

Back 106

data from points along any corneal meridian are always referenced to their own individual radii of curvature. do not average data and are necesssary for refrative surgery where local variation of corneal curvature is critical to vision and laser reshaping.

Front 107

forme fruste

Back 107

mild minimal keratoconus that can go unnoticed for a while as VA can be 20/20 because steepening is only in the periphery.

Front 108

Sim K

Back 108

determined from power points on mires 7-9. 3 mm central zone.

Front 109

SAI or surface asymmetry index

Back 109

determined from the summed differences in corneal power between corresponding points 180 degrees apart on the mires over 128 equally spaced meridians on 4 central mires. Not highly correlated with best spectable VA, but can be used to monitor changes over time.

Front 110

SRI, or surface regularity index

Back 110

evaluates localized irregularity between adjacent rings over 256 hemi-meridians. SRI approaches zero for a perfectly smooth surface. High correlated with best spectable corrected visual acuity.

Front 111

Minimum center thickness

Back 111

0.10

Front 112

Minimum edge thickness

Back 112

0.10

Front 113

Junctional thickness

Back 113

0.13

Front 114

Range of DK/t values

Back 114

0-21%, can't go higher than 21% because that's the content in air.

Front 115

In daily wear lenses dk/t value should be

Back 115

6-8%

Front 116

In extended wear lenses DK/t value should be

Back 116

17-18%.