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228 Cards in this Set

  • Front
  • Back
3 layers of the eye in order are
fibrous tunic, vascular tunic, nervous tunic
fibrous tunic (outer layer) consists of
sclera, cornea
vascular tunic (nourishment) consists of
iris, choroid, ciliary body
nervous tunic (photoreceptors & neurons) consists of
retina
3 fluid filled chambers of the eye are
anterior, posterior, & vitreous chambers
volume between the cornea & iris is known as
anterior chamber
volume between iris & lens is known as
posterior chamber
anterior & posterior chambers are filled with what watery fluid
aqueous humor
the ciliary body produces
aqueous humor
what does aqueous humor do
maintains IOP and provides nutrients to the lens & cornea
aqueous humor is continually drained from the eye thru
Canal of Schlemm
the greatest volume found between the retina and lens is
vitreous chamber
a thicker gel like substance which maintains the shape of the eye is
vitreous humor
light enters the eye thru the
transparent, dome shaped cornea
5 layers of the cornea are
epithelium, Bowman's membrane, endothelium, Descemet's membrane, & stroma
epithelium and bowman's membrane do what
protect the cornea from injury
epithelium has the ability to
regenerate quickly
bowman's membrane provides
a tough, difficult to penetrate barrier
removes water from the cornea, keeping it clear
endothelium
endothelium rests on
Descemet's Membrane
makes up 90% of the middle layer of cornea, between bowman's & descemet's membranes
stroma
from the cornea, light passes thru the
pupil
the amount of light thru the pupil is controlled by the
iris, colored part of the eye
the dilator & sphincter muscles are
the 2 muscles of the iris
opens the pupil allowing
more light into the eye
dilator muscle
closes the pupil, restricting light into the eye
sphincter muscle
has the ability to change the pupil size from 2 millimeters to 8 millimeters
iris
purpose is to focus light on the retina, lying just behind the pupil
crystalline lens
process of focusing on objects based on their distance is called
accommodation
the closer an object is to the eye, the more power is required of the _________
to focus the image on the _____
crystalline lens, retina
The crystalline lens achieves accommodation with
the help of
the ciliary body which surrounds the lens
The ciliary body is attached to the lens via
fibrous strands called zonules
when the ciliary body contracts, the zonules relax allowing
the lens to thicken, adding power, allowing the eye to focus up close
when the ciliary body relaxes, the zonules contract drawing
the lens outward, making the lens thinner, and allowing the eye to focus at distance
light reaches its final destination at
the retina
retina consists of
photoreceptor cells called rods and cones
sensitive to light and are suited for nite & peripheral vision
rods, 120 million in retina
have the primary function of detail and color detection
cones, 6 million in retina
center of the retina containing 6 million cones
fovea
corresponding colors to 3 types of cones are
red, green, or blue
signals received by the cones are sent via the ______ to the brain where they are interpreted as _____
optic nerve, color
people who are either missing or deficient in any one type of cone are
color blind
refractive errors occur when
abnormalities of the eye prevent the proper focus of light on
the retina
refers to an eye free of refractive errors
emmetropia (normal vision)
2 common types of refractive errors are
myopia and hyperopia
occurs if the eye is longer than normal or the curve of the cornea is too steep, causing light rays focus in front of the retina
myopia, (near-sighted)
are able to see objects at near, but distant objects appear blurred
myopia
can be corrected with minus power lenses
myopia
occurs if the eye is too short or the curve of the cornea is too flat, causing light rays to focus behind the retina
hyperopia, (far-sighted)
are able to see objects at distance, but near objects appear blurred
hyperopia
mildly hyperopic patients may be able to see clearly at near without correction by
using accommodation to compensate
can be corrected with plus power lenses
hyperopia
more common type of refractive error is
astigmatism
occurs when the cornea has an oblong, football-like shape in one or more directions (or axis) causing light rays to focus on more than one point on the retina
astigmatism
can be compensated for with cylinder power lenses
astigmatism
moves the eye upward and slightly outward
superior rectus
moves the eye downward and slightly inward
inferior rectus
moves the eye outward and downward
superior oblique
moves the eye outward and upward
inferior oblique
stabilization of eye movement is accomplished by
6 extraocular muscles
addition to movement and tracking, extraocular muscles maintain
alignment between
the eyes
when the eyes are properly aligned, the brain is able to
fuse the disparate images received by each eye into a single image
if any of the extraocular muscles are stronger or weaker than they should be, eye alignment can be affected by
making fusion difficult or impossible
difficulty with fusion can cause double vision, also known as
diplopia
when the brain "turns off" one image in an effort to eliminate diplopia is called
suppression
when the eye has a tendency to turn from its normal position it's called a
phoria
when the eye has a definite or obvious turning from its
normal position, it's called a
tropia
meaning outward or in a temporal direction
exo (exotropia)
meaning inward or in a nasal direction
eso (esotropia)
means up
hyper (hyperphoria)
means down
hypo (hypophoria)
electromagnetic energy travels at the speed of light =
186,000 miles/sec, in the form of a wave
we classify electromagnetic energy according to its
wavelength
the distance between two corresponding points on two consecutive waves
wavelength
electromagnetic wavelengths range in scale from that of an
atomic nucleus (gamma rays) to that of a small planet (radio waves)
one billionth of a meter
nanometers (nm)
the wavelengths of the visible spectrum lie between
400 and 700nm, with red light at the longer end of the spectrum and violet light at the shorter end
visible spectrum is
ROY G BIV
just below the visible spectrum
1 to 400nm lies ultraviolet (UV)
just above the visible spectrum
750nm to 1mm lies infrared
(IR)
as light moves from
one transparent medium to another, at any angle other than perpendicular to the material surface, the change in speed will also result in a change in direction =
refraction
principle that allows the creation of optical lenses that alter the path or focus of light
refraction
index of refraction (n) can be
calculated using the following equation:
n = speed of light in air / speed of light in selected material
CR-39 Plastic:
1.49
Crown Glass:
1.52
polycarbonate:
1.58
high index plastics:
1.60 - 1.74
high index glass
1.60 - 1.80
in a plus power lens, light rays
converge
point at which light rays converge
focal point
focal point in plus lens is
behind the lens surface
focal point in minus lens is
in front of the lens surface
lens power is expressed in
diopters (D)
power =
1/Focal Distance
Light rays pass through a lens and converge 0.50 m from the lens. What is the power of the lens?
Power = 1 / 0.50 m

Power = 2.00 D
can be used to correct strabismus
prism
occurs when eyes aren't aligned
double vision
occurs when brain "shuts off" one eye
monocular vision & loss of depth perception
cross - eyed
strabismus
occurs when images are seen by both eyes, or eyes see the same image
fusion
prism is measured in
diopters (Δ), but measured differently than lenses
2 ways direction of prism is specified
prescriber's method, 360* method
base up, base down, base in, base out
prescriber's method
base in =
nasal
base out =
temple
labs use this method to describe base direction of prism
360*, 180*
360* resultant prism equation =
R = Sqrt( V^2 + H^2 )
v = vertical prism
h = horizontal prism
360* resultant angle equation =
Tan(Δ) = V/H
prism by decentration =
induced prism
prism in diopters (Δ) is = to decentration distance (c) in
centimeters x the lens power (D)
prentice's rule (Δ = cD)
the corrective power of a lens is determined by adding the front curve to the back curve, equation:
+6.00 D + -2.00 D = +4.00 D
+4.00 D + 0.00 D (pl) = +4.00 D
+2.00 D + +2.00 D = +4.00 D
occurs as the eye moves away from the optical center of the lens, the lab will choose curves to minimize this
aberrations
lenses with curves chosen to minimize aberrations are called
"corrected curve" or "best form" lenses
is curved along a single axis and flat along the perpendicular axis
cylinder curve
the focus of a spherical curve is
a single point
the focus of a cylinder curve is
a line
the meridian along which there is no cylinder power in the lens and consequently the meridian of the cylindrical focus is
the cylinder axis
expressed in degrees between 0 and 180
cylinder axis
lens that combines spherical and cylinder curves is called
a compound lens or toric
measures lens curve surface
lens clock or lens measure
total power equation =
(F1 + F2 = FTotal)
defined as lenses that are non-spherical
aspheric
transpose a prescription written in plus cylinder form to minus cylinder form by
1. Add the sphere and cylinder powers to determine the new sphere power.
2. Change the sign of the cylinder.
3. Change the axis by 90 degrees.
transpose -3.00 +2.00 x 30
-1.00 -2.00 x 120
reflectance =
R = (n - 1)2/(n + 1)2 * 100%
Thus a material of refractive index 1.5, has a reflectance of
(0.5/2.5)2*100 = 4% per surface
describes the amount of light (usually specified for a given waveband) that will pass through that material
transmittance
glass pros
Superior optics
Stable material
Scratch resistant
glass cons
Does not accept tint
Not impact resistant
Heavy
CR-39 pros
Lighter than glass
Readily tintable
Less likely to fog
CR-39 cons
Susceptible to scratching (correctable by coating)
Lower index of refraction makes it less suitable for higher powered prescriptions
polycarbonate pros
Thinner and lighter than glass and plastic
Highly impact resistant (used for safety glasses)
Inherent UV protection
polycarbonate cons
Poor optical quality
Susceptible to scratching (correctable by coating)
Susceptible to stress fractures in drill mounts
Does not readily accept tint
hi-index pros
Thinner and lighter than glass and plastic
Better optical quality than polycarbonate
polycarbonate cons
Susceptible to scratching (correctable by coating)
Susceptible to backside and inner-surface reflections (correctable with AR)
trivex pros
Impact resistance of polycarbonate
Better optical quality than polycarbonate
Tintable
Lightest material on the market
Inherent UV protection
High tensile strength (ideal for drill mounts)
trivex cons
Susceptible to scratching (correctable by coating)
is not only perceived by
others as glare, but also represents a loss of light transmitted through to the eye
reflected light
minimizes lens surface reflections, reducing eye strain, while allowing more light to reach the eye, improving contrast and clarity
AR coating
light waves undergo destructive
interference and effectively cancel each other
AR coating
states that energy can neither be created nor destroyed
The Law of Conservation of Energy
what happens to the energy from the cancelled light waves?
it's transferred through the lens medium to the patient’s eyes
improving contrast and clarity!
defines a lens with a characteristic of changing state
from clear to sunglass dark when exposed to light
photochromic
4 types of photochromic lenses
transitions, PGX/PBX, Sunsensors, Life RX
removes glare and improves visual quality, creating detail, color, & contrast
polarized
light waves coming directly from the sun vibrate in all directions and are considered
non-polarized
when vibration is restricted to a single direction or plane, the light is considered
polarized
when non-polarized sunlight is reflected by surfaces, it can become
polarized (all but a single angle is either absorbed or scattered)
Bright, flat
surfaces such as water, wet roads, sand, snow, car hoods, and windshields are major
sources of
reflected polarized light
blocks the transmission of light from certain angles while allowing it from other angles
polarized len (venetian blind)
cross hatch pattern is
induced visible stress
protects the lens from
abrasions and scratches
scratch resistant coating
4 main types of coatings
dip, spin, in mold, vacuum
added to CR-39 lenses to increase the absorption of harmful UV rays
UV coating
Have a minimum center thickness of 3.0mm regardless of lens material; or
• Have a minimum edge thickness of 2.5 mm if it is a+3.00D lens or higher
• Pass a drop ball test of a 1 inch diameter steel ball dropped 50 inches
• Sandblasted with the manufacturer’s identification
• be delivered to the wearer bearing a Warning Label indicating that the protector
only meets the Basic Impact Standard
Basic impact lenses
Have a minimum center thickness of 2.5 mm regardless of lens material
• Pass a high velocity test in which a ¼ inch steel ball is shot at a lens at 150
ft/second
• Sandblasted with the manufacturer’s identification and a plus (+) sign
• Be manufactured from either polycarbonate, Trivex, or SR-91
High impact lenses
These frames are able to retain a lens during high impact testing
Z87+
a condition in which the eyes have unequal refractive power
Anisometropia
bicentric grinding, is a method of correcting vertical imbalance for patients with anisometropia
Slab-off
In some cases, one eye will be myopic while the fellow eye
is hyperopic, a condition known as
antimetropia
unequal
refractive powers result in differing amounts of induced prism as the eyes move away
from the optical center of the lenses, often causing
diplopia or double vision
may
be corrected by adding Base Up prism (slab-off) or Base Down prism (reverse slab-off)
to one or both spectacle lenses
diplopia or double vision
an opacity in the crystalline lens of the eye; a cloudiness that occurs in some of us as we age
cataract
to restore clarity, this is removed from the eye
crystalline lens
eye loses its natural ability to focus and is referred to as
aphakic
Most cataract surgeries today are followed by the insertion of this
IOL (intra-ocular lens)
helps restore the eye’s ability to
focus
IOL implant (pseudo-phakic)
if an aphakic patient wants to see both far and near out of one pair of glasses, they will need
a multi-focal lens of some type
based upon the idea of drawing an imaginary box around a lens shape with the box's sides tangent to the outer most edges of the shape
boxing system
horizontal distance between the furthest temporal and nasal
edges of the lens shape or the distance between the vertical sides of the box
"A" measurement
"A" measurement is also commonly known as
eyesize
vertical distance between the furthest top and bottom edges of the lens shape or the distance between the horizontal sides of the box
"B" Measurement
horizontal line that runs through the vertical center of the frame
datum
intersection of the Datum Line and horizontal centers of each lens shape
geometric center (GC)
shortest distance between the nasal edges of each lens or the distance between boxes
distance between lenses (DBL)
DBL is also commonly referred to as
bridge size
horizontal distance between the geometric centers of the lenses
distance between centers (DBC)
DBC is also know as the
geometric center distance (GCD) or frame PD
Twice the distance from the geometric center of the lens
furthest edge of the lens shape
effective diameter (ED)
is
used in combination with decentration distance to select the minimum lens blank size
required to fit a given frame
effective diameter (ED)
vertical distance between the bottom edge of the box and the top of the bifocal or trifocal segment
seg height
vertical distance between the Datum line and the top of the bifocal or trifocal segment Overall
seg drop
he running distance between the middle of the center barrel screw hole and the end of the temple
temple length (OTL)
distance between the center of the barrel and the middle of the temple bend
length to bend (LTB)
distance between the plane of the front of the frame and the
temple bend. Used if there is a significant distance between the frame front and the beginning of the temple
front to bend (FTB)
the combination of eyewires, bridge and the end pieces, also known as frame front
chassis
pieces that hold the chassis to the head and ears, also known as temple arms
temple
usually removable plastic sleeves that slip over the ends of
metal temples
temple tips
the area between the two eyewires
bridge
small pads designed to contact the nose and hold the frame
up off the nose and away from the face
nose pads
he small wire arms that actually hold the nose pad in place
guard arms
the area of the frame that actually surrounds the lens and holds the lens in place
eyewire
the area of the chassis that meets the temple or the point
where the temple attaches to the chassis, where half hinge is found
end piece
the point where the temple is connected to the chassis, allowing temple to fold
hinge
2 basic kinds of frame materials
metal & plastic
4 general types of metal frames
monel (nickel), stainless steel, titanium, memory metals (titanium mix)
makes up bulk of plastic frames on the market
zyl or zylonite
also known as library temple,
cable temple
things to consider for frame fit, rule of 3
width, nose, temple,
secondary frame fit considerations
pd, rx
standard or bench alignment
4 point touch
X-ing of eyewires =
twisting of bridge
should overlap and be near parallel with the top of the frame
proper temple fold alignment
the junction of each ear ,the skull, and the bridge of the patient’s nose
fitting triangle
for good cosmetics and optics, there should be 8-10* of this
pantoscopic tilt
particularly if the patient’s PD is narrower than the frame PD, this adjustment is helpful
positive face form
4 nose pad adjustments
width, frontal angle, splay angle, vertical angle
nose pad adjustment that should only be used to raise or lower multifocal segments, or OC height
cal height
a microscope used to measure the back focal length of a lens
lensometer, (vertometer, lensmeter)
instrument used to measure pupillary distance
pupilometer
instrument used to measure vertex distance
distometer
instrument used for visualizing & measuring lens stress
polariscope
ASTM
American Society for Testing Materials
ANSI
American National Standards Institute
OSHA
Occupational Safety and Health Administration
FDA
Food and Drug Administration
highly reflective and used to reduce light transmission through lenses
mirror coatings (vacuum)
larger lens is referred to as the carrier, while the smaller lens is typically called the segment
multifocal
the first multifocal (double spectacles) lens was created by
benjamin franklin (1750’s)
gives the ratio of the base curve to the addition created
(n – 1) / (ns – n)
n = index of the main lens
ns = index of the segment
an example of this is made by grinding various curves onto the back of a single vision lens blank
myoter bifocal
a 22mm round bifocal with a 2-3mm transition zone which blends the two curves together
seamless bifocal
types of multifocals
Flat Top – 25mm, 28mm, 35mm, 45mm, 7x28mm, 8x35mm, Double D 28mm,
Double D 35mm, Quadrifocal 28mm
Curved Top – 28mm
Round – Achromat, Kryptok, Ultex, 22mm, 25mm, Double Round
Panoptik
Ribbon
Executive – Bifocal, Trifocal, ED Trifocal
good procedures to follow for the fitting of multifocal lenses:
1. Adjust the frame and nosepads, 10mm - 14mm vertex distance.
2. keep your eyes on the same plane as the patient and parallel to the floor.
3. For FT, Executive, or Round bifocals, mark the lower lid margin on the demo
lens. For FT, Executive, or Round Trifocals mark the position of the lower pupil
margin, For Seamless bifocals place your mark at the lower lid margin then add a mm to the segment height
abrupt change in the position of an image due to the change in power and corresponding prism
image jump
To determine the amount of jump created by a segment the following formula applies:
find the optical center of the segment
FT Designs (below top of segment)
SegOC = (width – height) / 2
For Round Designs (below top of segment)
SegOC = width / 2 = height / 2
Jump = amount or prism or image jump
Add = multifocal add power
SegOC = from above the measure in mm of the optical center from the top of the segment
Jump = Add x SegOC /10
used to treat presbyopia
Progressive addition lenses (PALs), commonly referred to as no-line bifocals or varifocals, avoiding image jump but causing some distortion
first commercially available PAL was designed by
Duke Elder in 1922 named the “Ultrifo”
PAL fitting method for good technique to follow is:
1. Make sure the frame is 10mm -14mm of vertex distance.
2. Adjust the nose pads, Apply 5°-10° of face form, and 10° – 15° of pantoscopic tilt
3. Keep your eyes on the same plane as patient, parallel to the floor, mark the centers of pupils on demo lenses
4. Measure the distance from the pupil center on the lens to the inside bevel of eyewire. This is the segment height
5. Use the manufacturers cut out chart to verify that the DRP, NRP, PRP are
properly placed and within the confines of the frame.
Take monocular IPD with a corneal reflex pupilometer, double checking measurement