NCSORB Flashcards
Rods number 125 million & are responsible for ____ vision.
Night vision, black & white, motion, peripheal
Cones number about 6 million & are responsible for ___ perception
Day vision, detail, visual acuity, color
When measuring a frame PD with a ruler you should measure from the inside temporal edge of one eyewire, across the bridge, to which part of the opposite eyewire?
inside nasal edge
Glacuoma is caused by an increase in ___ in the eye
pressure
What does OC stand for
optical center
The focal point for a minus lens occurs ___ of the lens
in front
A polarized lens cuts out vertical or horizontal light
horizontal
What is the thinnest an industrial safety lens should be
3 mm
a multifocal lens style that provides a slow increase of a plus power from the distance portion of the lens to the near zone is called
progressive
the crystalline lens has a focal power of approx _____ diopters
twenty
What are the six muscles which allow the eye to move in different directions?
Internal (medial) rectus- in to nose
External (lateral) rectus- out to ear
Inferior rectus- down and out
Superior rectus- up and in
Inferior oblique- up and out
Superior oblique- down and in
How do you calculate minimum blank size
double the decentration & add it to the ED of the frame, then add 2
MBS= ED + (2X Decentration) + 2
What size SV lens blank would be the smallest possible for the following frame
A=54 B=40 ED=56
distance decentration= 5mm
Rx -10.00 -1.00X180
68
10+56+2=68
What is the standard for measuring spectacle tolerances
ANSI Z80.1
What year was the Boxing System introduced and by whom?
1962
Optical Manufacturers Association
which bifocal lens is not a once piece construction: A) plastic round 22 B) flat top 28 glass C) progressive plastic D) glass executive
B
flat top 28 glass
what is the index of the cornea
1.37
-3.00 +2.00 x135
is called what
compound myopic astigmatism
where is the posterior chamber
directly behind the iris and in front of the crystalline lens
this lens is the least dense available
A) CR-39
B) glass
C) hi-index
D) poly
CR-39
a patient comments that his old glasses gave him much better visual acuity than the new pair. after examining the glasses you find that both pairs have the same Rx. What should you do?
A) send the patient back to the doctor
B) check base curve, face form and tilt
C) remake entire pair of glasses
D) place new lens in different frame
B
check base curve face form and tilt
What is the index of flint glass
1.65
How many layers are there in the retina
ten
-1.00 +3.00 x180
is called what
mixed astigmatism
A plus lens moved ___ creates base in prism
in
a lens clock can be used to check the:
A) center thickness of a lens
B) nominal surface power of a lens
C) refractive power of a lens
D) tempering of a lens
C
refractive power of the lens
if a +16.00 diopter lens is moved closer to the eye, what effect would this have on the effective power
A) less plus
B) more plus
C) prism is created
D) no change
a
less plus
a ___ lens moved in creates base out prism
minus
a patient is complaining of pressure on the nose and behind the ears with his frame, what two things do you need to adjust to correct the problem on a plastic frame?
A) temple bend
B) lens mounting chord
C) temple bend and bridge
D) temple bend, lens mounting chord & pantoscopic angle
C
temple bend and bridge
light rays passing through a plus lens actually ____
intersect/ converge
the limbus of the eye is adjacent to the
cornea
what does the “7” in “7X28” trifocal mean
height of the intermediate window
What do BU and BD stand for
base up & base down
What is the index of PMMA plastic (plexiglass)
1.49
a -475 spherical lens decentered 4mm produces
1.9 prism diopters
(prentice rule: -4.75 * .4= 1.9)
blockage of the canal of schlemm produces primarily what
glauoma
What is the Canal of Schlemm
the canal that drains the aqueous humor from the anterior chamber of the eye and drains into the venous system (blood)
what is the number of major (external) muscles that control eye movement
six
what is the index of poly
1.59
where is the sclera located
front portion, or “white” of the eye
what is the area between the iris/pupil and the cornea called
anterior chamber
what is the index of the crystalline lens
1.42
bifocal adds are correctly verified when the optican checks the add from which side of the lens against the lens stop
front
which lens material is the most impact resistant
poly
___ is the absence of the crystalline lens of the eye, if not replaced with an artificial intraocular lens
aphakia
when a cataract patient has had an intraocular lens (IOL) inserted they are
pseudophakic
the inability to accomodate is
presbyopia
when verifying a pair of glasses in the lensometer to determine if any vertical imbalance is present, it is accepted industry practice to start with
The lens with the strongest power in the vertical (90 degree) meridian
determine the binocular horizontal decentration for the following
Frame PD is 75mm
Patients binocular PD is 69mm
6mm
a condition of the cornea in which the cornea asssumes a cone shape is called what
kerataconus
what is the minimum height for a FT Trifocal
18mm
what are the five layers of the cornea
Epithelium
Bowmans Membrane
Stroma
Descemets Membrane
Endothelium
when light rays come to two separate points of focus, one on the retina & one in front of the retina it is called
simple myopic astigmatism
what is cellulose acetate
plastic/zyl frames
when a frame for a six year old child is selected, a saddle bridge is a better choice than a comparable frame with adjustable pads for which of the following reasons:
A) adjustable pads and their guard arms may be a hazard if the child falls
B) a saddle bridge distributes weight over a greater portion of the nose
C) a saddle bridge retains adjustment better than an adjustable pad
all of the above
what index is water
1.33
the area where the upper and lower eyelids meet, also containing tear ducts is called
canthus
the focal length for a plus lens is referred to as ___
postive
what does the lens clock do
measures base curve
concave surfaces curve what way
inward
when fitting a patient with trifocals, what is the usual point of reference for the fitting height
lower pupil margin
what metal, used for frames, is strong, resistant to corrosion, and stable under high temperatures
titanium
which coating/tint will increase the transmission of light through a lens
anti-reflective
what are the four basic uses of prism lenses
1) relieving prism: made for a weak muscle, the base is placed over the deficient muscle
2) stimulating prism: used to stimulate a lazy muscle. the apex is placed over the muscle
3) measuring prism: used to measure the strength of a muscle or a group of muscles
4) dissociating prism: used to effect a temporary destruction of fusion to determine the muscle problem
vertex distance is:
the distance from the back/posterior or ocular surface of the lens to the front/anterior surface of the cornea
when light rays come to two separate points of focus, one in front of and one behind the retina, it is called
mixed astigmatism
the vitreous chamber takes up approx ___ of the eye
2/3
when light rays come to two separate points of focus, one on the retina and one in front of or behind the retina is calld
simple astigmatism
when light rays come to two separate points of focus, one on the retina and one behind the retina it is called
simple hyperopic astigmatism
___ is a drooping of the upper eyelid
ptosis (blepharoptosis)
-.50 -0.25x180
is called what
compound myopic astigmatism
a polariscope is used to
measure lens stress (determine if lens has been heat treated)
a transparent, gel-like substance that fills the space between the crystalline lens and the retina is called
vitreous humor
what is a lens caliper used for
measuring lens thickness
the focal point for a plus lens occurs ___ the lens
behind
what is the reticle center of a lensometer used for
reading lens power
the line drawn directly across a lens shape at the 180 line is called
datum line
the tissue membrane lining the inside back of the eye, which contains the sensory receptor cells that collect light energy is called what
retina
determine the vertical decentration
B= 51
Patients OC 32 mm
6.5 mm up
a minus lens moved out creates ___ prism
base in
what muscles dialate in dim light
dialator
prism is
a wedge shaped piece of optical medium with a base and an apex. a prism has no focusing power, it deviates light
when light rays do not form a single point focused on the retina it is called
astigmatism
when light rays come to two separate points of focus, both on the same side of the retina it is called
compound astigmatism
Iseikonic Lenses
- Lenses designed to increase or decrease the spectacle magnification of the lens without changing its back vertex dioptric power
- Used to correct aniseikonia
- aniseikonia is= an ocular condition where there is a significant difference in the perceived size of images
what is the minimum height for a flat top bifocal
11 mm excluding sports relating fitting
what is the bony socket that surrounds and protects the eye while providing a structure for attachment of the ocular muscles called
orbit
what muscles constrict the pupil in bright light
sphincter
phoria is a ____ for the eye to ___ ___ from its normal position
tendency, away from
strabismus is commonly known as
crossed eyes
or
squint
what is the major refracting body of the eye
cornea
what is the densest lens available
poly
+100 +200 x090
is called what
compound hyperoptic astigmatism
slab off is grinding away the ___ surface of the lens
back
bicentric grinding (slab off) is done on only on lens. the ___ minus or ___ plus. the prism that results is ___
most minus, least plus, base up
what does PD stand for
Pupillary distance
how many layers are there to the cornea
five
a network of nerve fibers that send impulses from the retina to the brain for interpretation as visual images is called what
optic nerve
a definite turn of the eye is called
tropia
how do you calculate proper base curves for minus lenses
1/2 the spherical equivalent and add +6.00
loss of elasticity of the lens leads to what
presbyopia
define A B ED and DBL
A= temple to nose B= top to bottom
ED= (effective diameter) corner to corner
DBL= (distance between lenses) bridge
clouding of the crystalline lens is
a cataract
what takes more material than glass to bend the light rays
cr-39
on the power drum of a lensometer, which power values are black and which are red
plus is black
minus is red
convex surface curves what way
outward
a plus lens moved ___ from the eye gains plus power
away
the muscle that controls the amount of incoming light, commonly referred to as ‘the colored part of the eye” is
the iris
antimetropia means one eye is ___ and the other eye is ____
myopic, hyperopic
located directly behind the iris, this lens is ____ in shape
biconvex
the three principal parts of the eyes optical system are
cornea, crystalline lens, & retina
what is the index of crown glass
1.523
the focal length for a minus lens is referred to as
virtual
what is the best way to measure for a flat top bifocal
from the lower eyelid
what are the three ways to measure pupilary distance with a PD ruler
from the center of each pupil
from the inner corner of one pupil to the outer corner of the other
from the inner corner of one iris to the outer corner of the other
what is the macula
the small area of retina that surrounds the fovea and that, with the fovea, compromises the area of the retina that gives distinct vision. contains most of the cones
what is the fovea
a small depression in the retina at the back of the eye, the part of the macula adapted for the most acute vision
what are the three nose pad angles
frontal angle, splay (spread) angle & verticle angle
a minus lens moved closer to the eye ___ minus power
gain/increases
a plus lens moved out creates ___ prism
base out
composed of skin and fleshy tissue, which provide a protective covering for the eye is called what
eyelid (palpebra)
plano -100 X045
is called what
simple myopic astigmatism
what is the usual product an optician provides when helping a patient who is being treated for amblyopia
an occulder
determine the monocular horizontal decentration for the following:
Frame PD 76
Patients monocular PD
OD 32/ OS 33.5
OD 6mm
OS 4.5 mm
when dropball testing a safety lens a ___ inch ball is dropped from ___ inches
1 inch
50inches
light rays passing through a minus lens have an ___ point of intersection
imaginary
what year was “Duty to Warn” implemented and what is it
1987
Duty of the offices to warn patients about the impact resistance of various lens materials
what contains all the sensory receptors for the transmission of light
retina
the word that means “double vision” is
diplopia
the anterior chamber contains a fluid called what
aqueous humor
when light rays come to two different points, both behind the retina it is called
compound hyperopic astigmatism
what is the minimum height for a blended bifocal
12mm
to compensate for the 1-2 mm band of blured vision around the seg
where is the retina located
the lining located at the inner backside of the eye
what index is air
1.00
when a light ray strikes a prism it is deviated toward the ___ but the ___ is displaced toward the ___
base, image, apex
when light rays come to two separate points of focus, both in front of the retina it is called
compound myopic astigmatism
where is the vitreous chamber located
between the posterior surface of the crystalline lens and the back of the eye
What does OU stand for
occli uterque
both eyes
What does OD stand for
occulus dexter
right eye
what does OS stand for
occulus sinister
left eye
the aqueous humor has an index of refraction of
1.33
scotoma: detachment of ___ and ___ caused by a sharp blow or injury to the head
rods, cones
the white tissue that covers the front surface of the eye which protects and shapes the eye is called
sclera
what has up to approx 40 diopters of power
the cornea
what do the letters DBL represent
distance between lenses (bridge size)
which of the following are layers of the cornea: A) Bowmans Membrane B) Sclera C) Stroma D) Meibomian
a & c
Bowmans Membrane and Stroma
what is the index of a high index lens
1.60
this lens has more molecules than CR-39 but less than high-index
glass
what are the receptors called for the retina
rods and cones
a heat-treated or chemical hardened lens loses some of it’s impact resistance when it is
a) exposed to extreme cold
b) heated in a frame warmer
c) used for too many years
d) scratched or pitted
scratched or pitted
vertex distance is most important when fitting which of the folowing
a) multifocal
b) plastic lenses
c) glass lenses
d) Rx + or - 7 diopters
Rx + or - 7 diopters
plano +1.75 x45 is called what
simple hyperoptic astigmatism
which portion of the UV spectrum is considered harmful to the eyes
UVA and UVB
what type of bridge design makes a long nose appear shorter
low positioned saddle bridge
the opening in the iris through which incoming light rays pass is called
pupil
which instrument can be used to measure vertex distance
ruler and distometer
___ diopter of prism diverts a ray of light ___cm from its original path at ___ meter
1/1/1
1 prism diopter moves light 1 cm away from 1 meter distance
a lens whose power is four diopters has a focal length of
25 cm
focal length is 1/power so 1/4 =.25
.25=25cm
how many inches are in a meter
39.37
what is the speed of light
186,000 miles per second
a lens that has two curves on the front surface is
plus cylinder lens
from when lenses used to be ground on the front surface
hyperoptic lenses for presbyopic patients have what prismatic effect in the reading area
base up
plus lenses are up under the oc, minus lenses are down under the oc (patients look down to read)
what does MRP stand for
major reference point
the MRP is located at the OC when…
no prism is prescribed
with a (Geneva) lens clock you find: front curve= +8.25
back surface highest curve= -6.50
back surface lowest curve= -4.75
what is the power of the lens
+3.50 -1.75
D1 (front curve) + D2 (back curve)= Dt (power)
+8.25 + -6.50= +1.75
+8.25 + -4.75= +3.50
distance between the two powers in the major meridians is the cyl, being 1.75. sign of the cyl is determined by direction of travel from one power to the next
looking 5mm above the oc of a lens power of +1.50 -0.50 X180 you will experience what prismatic effect
a)0.75 diopters BU
b) 0.50 diopters BD
c) 1.00 diopters BD
d) 0.50 diopters BU
0.50 diopters BD
oc is below the pupil, vertical meridian (90) +1.00 is power at 90 (+1.50) + (-0.50)= +1.00
prentice rule= .5 cm * 1=.50
BD because oc is below the pupil: plus lenses move the same direction, minus lenses move opposite
the standard for sports glasses was developed by
ASTM
American Society for Testing Materials
what factors are considered in computing the power of a thick lens
front curve
back curve
thickness
index
which Rx is written incorrectly
a) +1.00 -1.00 X 180
b) PL +2.50 X 100
c) +2.75 -1.50 X 90
d) +3.00 -1.25 x 145
c +2.75 -1.50 X90
axis should be written as 090
all figures must be written with three digits
what is a kryptoc
a brand name of round seg bifocals
longest vertical dimension of the seg is called
seg depth
zylonite is also known as what
cellulose nitrate
this was banned by the FDA as a frame material due to its flammability
the geometric center of a frame is the same as
A + DBL
GCD is also called Frame PD
if a patient has a symmetrical face and a monocular PD of 63/60 what is the monocular near PD
30
a glassblowers lens is commonly known as
Didymium lens
a trade name for special lenses designed to block infrared light from molten glass
what are palpebra
eyelids
what are conjuctiva
mucus membrane that lines the underside of each eyelid
what is an incident ray
the original ray of light that hits a surface or material
what is supraversion
both eyes move up
what instrument measures the curvature of the center cornea
keratometer
how many nanometer is A band ultraviolet light (UVA)
330-400nm
what is inset
halfway between distance pd and near pd
which UV spectrum is completely absorbed by the atmosphere
UVC
what are the three types of plastic bridge types
keyhole, saddle, modified saddle
which of the following is not used for correcting vertical imbalance at the reading level
a) unequal add powers
b) compensated segments
c) bicentric grinding
d )dissimilar segments
unequal add powers
how many millimeters in an inch
25.4
a lens has a power of +1.00 at 90 and -1.00 at 180 what is the lens power
-1.00 +2.00 X180
the difference between +1.00 and -1.00 is 2 diopters, cyl is 2.00 if sphere is -1.00 then axis is 180 so -1.00 +2.00 X180
what are the three tunics of the eye
Fibrous tunic (outer) protective- contains cornea and sclera
Vascular tunic (AKA Uveal tract) (middle) nourishing- contains choroid, ciliary body & iris
Nervous tunic (AKA Sensory tunic) (inner) light sensitive- (retina)
what multifocal will reduce image jump the most
a) FT40
b) ST28
c) FT35
d) kryptok
FT40
the wider the seg, the higher the oc will be, higher oc = less image jump (further from the segment)
how many centimeters in a meter
100
1.0 meter = .01 centimeters
10 cm = 0.10 meter
15 cm = 0.15 meter
etc etc
the size of an image will always increase if you
increase base curve
what is the formula for finding the power at 90 or 180. what is it for 45 or 135
90 or 180 is sphere plus cyl power
45 or 135 is sphere plus half the cyl power
what percentage of the cyl power is in effect at:
30, 45, 60, & 90 degrees away from the prescribed axis
30= 25% 45= 50% 60= 75% 90= 100% ( 0% at prescribed axis)
conventional slab off is also referred to as what? what direction is the prism ground in?
bicentric grinding
base up
(reverse slab off is down)
what is abberation
the failure of a refracting surface to bring all rays from an object point to a desired image point
(it can result in image blur or the curvature in the image of a straight line. it may be inherent in the lens design or error in processing.)
at what age is the amplitude of accommodation the highest
a) 10
b) 20
c) 40
d) 50
10
amplitude (capacity) is highest in children and decreases with age
the law of refraction basically states what
light bends toward the normal when it enters a medium more dense than from which it came
what is the Major Reference Point
the point on a lens at which the specified distance prescription requirements shall apply
(commonly but imprecisely referred to as Optical Center)
what is the mechanical center of a lens
the point on the lens surface around which a lens is cut an edged
what is the limbus
where the cornea meets the sclera
(corneoscleral junction)
what is LTB
Length To Bend
a measurement for temple lengths
from the center of the hinge barrel to the center of the bend
how many diopters is the “1X” power on a microscope
+4.00 diopters
what is chromatism
an appearance of colored lights (abnormal coloration)
what is the frontalis muscle
brow muscle
gives the face more expression (raises eyebrows and wrinkles forehead)
what is optical infinity
20 ft (6 meters) or more
what is asthenopia
eye strain
what is the superior lens edge
the top edge of the lens
what is isometropia
refractive condition is the same in both eyes
what is the canthus
angles formed by the meeting of upper and lower eyelids
what is the index of trivex
1.53
what is the optic disc
area in the retina where blood vessels and optic nerve exit the eye
what is Muller’s muscle
short muscle that lifts the eyelid while you are awake. controlled by sympathetic nerves. if you are tired it relaxes the eyelid and your eyes will droop
what is a pantograph
a machine used to copy a plastic pattern onto a plastic sheet. pattern can be copied in a different scale if needed
what is ptosis
a drooping of the eyelid caused either by nerve weakness or paralysis
what is infraversion
both eyes move down
prism cannot be put into a lens with
no power
how many nanometers is B band ultraviolet light (UVB)
275-330 nm
what is the levator muscle
goes from back of eyeball, over the top and into the eyelid. lifts the eyelid out of the field of vision
what is levoversion
both eyes move left
what is dextroversion
both eyes move right
how many nanometers is C band ultraviolet light (UVC)
200-275 nm
How many nerve fibers are in the optic nerve
1.2 million
what is nystagmus
small repetitive involuntary rhythmic side to side or up and down movements of the eye
“shaking of the eyes”
what is the inferior lens edge
the bottom edge of the lens
what is the annulus of Zinn
ring-like structure at apex of orbit where the four rectal muscles meet
what is the lacrimal gland
produces tears, which flow across the eye to lubricate it
what is orthophoria
no deviation of the eyes
what is a retinoscope
instrument used to examine the refractive error of the eye
what is another name for nanometer
millimicron
what is a CRP
Corneal Reflection Pupilometer
what is a focimeter
an instrument used to determine vertex power, axis location, optical center, and MRP at a given point on an ophthalmic lens
also known as a vertometer or lensometer
what is a corrected curve lens
a lens that has been designed to reduce peripheral power errors for the conditions of intended use over a specified portion of the field of view
what is sagitta
vertex depth
the depth of the surface curve on a lens measured over a specific diameter
if a +10.00 lens is moved 5mm nearer the eye, it will be about
.50 weaker plus effective power formula EP= D/ (1-fD) 10*-.005= -0.05 1- -0.05=+1.05 10/1.05= 9.52 power is approx .50 diopters weaker plus (plus power moved closer is weaker plus)
what is scotoma
a blind area of reduced vision in the visual field (detachment of rods and cones)
what is anisometropia
a condition in which the refractive error of one eye significantly differs from the other, but both are myopic or hyperopic (same sign Rx) (greater than 2 diopters in difference)
what is ametropia
a refractive error in which the eye, when in a state of rest, does not focus the image of an object upon the retina. the general term for having either hyperopia, myopia, or astigmatism
what is amblyopia
loss of vision with out any apparent disease of the eye, usually because of “lazy eye”
a Geneva lens measure (clock) measures what
base curve
can also be used to find lens power based on curvature of front and back surfaces
a characteristic most CR39 lens series have in common is
minus cylinder form
in a minus powered lens light rays ___ and come to a focal point ___ the lens
diverge, in front of
fusion occurs in
the brain
what is fusion
the power of coordination by which the images received by the two eyes become a single image
what controls the amount of light entering the eye
iris
ANSI Z80.1 (2010) prism tolerances are:
vertical-
0-3.37= .33 diopters
greater than 3.37 = 1mm
horizontal-
0-2.75= .67 diopters
greater than 2.75 = 2.5mm
ANSI Z80.1 (2010) cylinder axis tolerances are:
0-.25 =14 degrees .25-.50= 7 degrees .50-.75= 5 degrees .75-1.50= 3 degrees greater than 1.50= 2 degrees
ANSI Z80.1 (2010) sphere power tolerances are
SV & MF
0-6.50= .13 diopters
greater than 6.50= 2% of power
Progressives
0-8.00= .16 diopters
greater than 8.00= 2% of power
ANSI Z80.1 (2010) cylinder power tolerances are
SV & MF
0-2.00= .13 diopters
2.00-4.50= .15 diopters
greater than 4.50= 4%
Progressives
0-2.00= .16 diopters
2.00-3.50= .18 diopters
greater than 3.50= 5%
ANSI Z80.1 (2010) add power tolerances are
0-4.00= .12 diopters
greater than 4.00= .18 diopters
how do you determine which type of astigmatism a prescription is ? (simple/compound myopic, simple/compound hyperopic, mixed astigmatism)
transpose the Rx from the original form, compare the new sphere power to the original sphere power.
if one is plus and one is minus, it’s mixed astigmatism
if both are plus or minus it is compound
if it is plano in one and either plus or minus in the other it is simple
how do you find the spherical equivalent of an astigmatic (toric) lens
add the sphere to one-half of the cylinder power, drop the axis
+1.00 +2.50 X 090= +2.25
what is the formula to find focal length
Fm= 1/D
Fm= focal length in meters D= power \+10.00 Rx: 1/10= .10 (.10 meters=10 centimeter) focal length is 10cm
a +12.00 lens is prescribed at a vertex distance of 13mm. the optican fits the glasses at 9mm. what is the power of the lens at that fitting position
a) +12.00
b) +11.50
c) +12.25
d) +10.50
+11.50
plus lenses moved closer to the face become weaker
How many millimeters in a meter
1000
1mm= 0.001 meter
5mm= 0.005 meter
10mm= 0.01 meter
how do you determine the effective power of a lens
EP= D/ (1-fD)
D= current power
f= difference in vertex difference measured in meters (1mm=0.001m)
f will be a positive number if it is moved further from Rx vertex distance, a negative number if moved closer to Rx vertex distance
what is the formula to find lens power at a focal distance
power= 1/ focal distance
if focal distance is 50cm
1/.5=2
power is +2.00
what type of lens is convergent
plus lens
what type of lens is divergent
minus lens
what is tempering
a process of heat treatment to make the lens more impact resistant
what is chem-tempering
A process of using potassium nitrate bath to make the lens more impact resistant. the process is called ion exchange because the smaller ions in the glass get replaced by the larger ions in the bath.
what are the four things that control magnification
the prescription, the front curve, center thickness and vertex distance
what is heterophoria
one eye, or both eyes, wander away fro the direction in which they should be so that the eyes are not looking in the same direction
what is reverse slab off
base down prism, done on the least minus or most plus lens
what is a tonometer
instrument that measures internal pressure of the eye
internal (lateral) rectus
moves the eye outwards
external (medial) rectus
moves the inwards
superior rectus
moves the eye upwards and slightly outward
inferior rectus
moves the eye downward and slightly inward
superior oblique
moves the eye outward and downward
inferior oblique
moves the eye outward and upward
If a bifocal has its segments on the _____ of the lens, then the lens must be made in minus cylinder form.
front
Light rays that come from ____ feet or more away are considered parallel.
20
how many millimeters should the OC be ___ per degree of pantoscopic tilt
.5 (1/2)mm per degree lower
How can you tell if a frame was made with the boxing or datum system?
Boxing system will have the labels “eyesize” and “DBL measurement” and datum system will have markings for “eyesize” and “bridge”. The boxing system will have small box between measurements on the frame and the datum systems will have x,- or / between measurements
What are symptoms of too much base down prism?
- Floors and other spaces that are flat and horizontal appear to be concave, so that the person has the illusion of being inside a bowl
- walls, buildings, and other vertical spaces appear to be taller than they actually are.
- surfaces seem to slope, so that a sidewalk or hallway seems to be going uphill.
what are the symptoms of too much base up prism
- floors and other spaces that are flat and horizontal appear to be convex, so that the person has the illusion of being on a little hill
- walls, buildings, and other vertical spaces appear to be shorter than they actually are.
- surfaces see to slope, so that a sidewalk or hallway seems to be going downhill.
what is the formula for finding prism
prentice rule
prism=power * decentration (in centimeters, 2mm= .2cm)
what index is the geneva lens measure calibrated to
1.53
an uncoated, normal plastic (CR-39) lens will reflect approx what percent of light
8%
92% transmitted
when two light waves are “in phase” they will
compound one another
what is Tenon’s capsule
a layer of tissue that lies between the surface of the eye and the conjunctiva
what is the ciliary body
attached to the outer edge of the iris near the wall of the eye. The ciliary body produces the fluid (aqueous humor) that fills the eye and nourishes its structures. It also helps to change the shape of the lens when focusing occurs.
When determining the bifocal add you should measure the difference between what
the back vertex measurement of distance and near
(the difference between the sphere power in the distance from the back of the lens and the sphere power in the near from the back of the lens)
the point on a lens where the prisms attach either base to base or apex to apex is
the optical center
what has the greatest effect on lens magnification
lens power
which of the following glass lenses is not a fused bifocal
a) curve top
b) straight top 28
c) executive
d) flat top 35
executive (in glass this is a one piece construction)
a prism seg is designed to provide which of the following at near only
a) BI prism
b) BO prism
c) BU prism
d) BD prism
a BI prism
prism segs are a seldom used method for correcting vertical imbalance
what is the approx dioptric power of the refractive system of the eye
usually between 58 and 62 diopters
a bifocal seg that is flat on top and bottom with a depth of 14mm is
ribbon seg
using the “360 degree” method, what are the directions of prism for each eye
0 degrees= BI for right BO for left
90 degrees= BU OU
180 degrees= BO for right BI for left
270 degrees= BD OU
“180 degree” method is same but 90 & 270 are still BU & BD
a ___ PD is given as one number
Binocular
binocular= both eyes together
a ___ PD is given as two seperate numbers
monocular
mono= one
the optical cross is a graphic representation used to show the ___ of a lens
meridian powers (total lens power)
as pantoscopic angle is increased
the spherical equivalent is increased
how do you calculate base curve for plus lenses
spherical equivalent plus +6.00
What is the specific gravity of CR-39
1.32
What is the ABBE value of CR-39
58
What percent of light is reflected from CR-39
4
What is the specific gravity of polycarbonate
1.21
What is the ABBE value of polycarbonate
29
What percent of light is reflected from polycarbonate
5.2
What is the index of refraction of trivex
1.53
What is the specific gravity of trivex
1.11
What is the ABBE value of trivex
46
What percent of light is reflected from trivex
4.4
What is the specific gravity of crown glass
2.54
What is the ABBE value of crown glass
59
What percent of light is reflected from crown glass
4.3
What is the specific gravity of flint glass
1.62
What is the ABBE value of flint glass
50-55
ANSI Z80.1 (2010) tolerance for specified base curve is
Plus or minus 0.75 diopters
What is the result if fusion cannot occur
Diplopia
What word in relation to tropia and phoria means out
Exo
What word in relation to tropia and phoria means in
Eso
What word in relation to tropia and phoria means up
Hyper
What word in relation to tropia and phoria means down
Hypo
What is emmetropia
No refractive condition
What is anisometropia
Where the refractive error of one eye differs significantly from that of the other but both eyes are either hyperopic or myopic (by 2 diopters or more)
What is antimetropia
When one eye is hyperopic and one eye is myopic
What is aniseknonia
A form of double vision that may occur when the image seen by one eye differs so much in size or shape from the other that the two images cannot be fused together by the brain.
Lazy eye is
Amblyopia (a loss of vision without any apparent disease of the eye)
If light comes to focus directly on the retina
Emmetropia
If light comes to focus at one point in front of the retina
Simple Myopia
If light comes to focus on one point behind the retina
Simple hyperopia
If light comes to focus at two points in front of the retina
Compound myopic astigmatism
If light comes to focus on two points behind the retina
Compound hyperopic astigmatism
If light comes to focus on two points, one in front of the retina and one behind the retina
Mixed astigmatism
When light comes to a focus with one point on the retina and one point in front of the retina
Simple myopic astigmatism
When light comes to two points of focus, one on the retina and one behind the retina
Simple hyperopic astigmatism
A refractive error when light does not focus on the retina
Ametropia
General term for any refractive error
What is the vascular intermediate coat of the eye that furnishes nourishment to the other parts of the eye
Choroid
Irregular astigmatism
When the principal meridians in the eye are not 90° apart
Regular Astigmatism
When the two principal meridians in the eye are 90° apart
What is the order of structures of the eye that light passes through from front to back
Cornea, aqueous humor, pupil, crystalline lens, vitreous humor, retina
Cilia
Eyelashes
Madrosis
Loss of eyelashes
Trichasis
Ingrown eyelashes
Stye
Purulent inflammation of infected eyelash follicles
How many times does the average person blink per minute
7-12 or 12-18 depending on study material
How large is the palpebral fissure
15mm high by 30mm wide
What is the palpebral fissure
The vertical space between the upper and lower lids
What are canthi
The angles formed where the upper and lower lids meet
Lateral canthus is where
Towards temples, outer angle of lids
Medial canthus is where
Towards nose, inner angle of lids
Caruncle
Pinkish part of the eye lid at the medial canthus that houses two accessory tear glands
What muscles close the lids
Orbicularis occuli
What muscles open the lids
Levator palbebrae superiorus
Müller muscle
Gives lids shape
A weakened muscle causes ptosis
Tarsal plates
Stiff tissue that goes over lids from canthus to canthus
Palpebral conjunctiva
Transparent mucous membrane the codes the insides of the eyelids
Bulbar conjunctiva
Mucous membrane that covers the sclera
How far does the upper lid move down during a blink
10-12mm
The bottom lid moves up and____during a blink
2-5mm nasally
The eyeball it self moves_____ inward in a forced blink and also rotates _____
1-2mm
Upward
What are the folds formed by the junction of the bulbar and palpebral conjunctiva called
Fornix
Superior fornix
Folds of conjunctiva behind upper lid
Inferior fornix
Folds formed by conjunctiva behind lower lid
Limbus
Transition zone between cornea and sclera
What is limbal engorgement
When the prominent blood vessels in the limbus are irritated and dilate (can be caused by allergens, infections, or foreign bodies including contacts)
Neovascularization
Caused by long-term corneal edema, the blood vessels from the limbus grow new structures and invade the cornea
Hypotonic cornea
More water flows into cornea than out. Occurs when normal evaporation isn’t allowed to happen. Cornea is thicker than normal (edema)
Isotonic cornea
Equal amounts of water flow in and out of cornea. Cornea is at normal thickness
Hypertonic cornea
More water flows out than into cornea. Can be caused by a higher salt concentration on the cornea. Cornea is thinner than normal
Zonular fibers
Attached to crystalline lens and ciliary muscles for accommodation
Ciliary muscles
Attached to zonular fibers for accommodation
Accommodation for distance vision occurs when
The ciliary muscles relax and the zonules contract, thinning the crystalline lens (more minus power in lens)
Accommodation for near vision occurs when
The ciliary muscles contract and the zonules relax, thickening the crystalline lens. (More plus power in lens)
Retinal detatchment
When the retina tissue pulls away from the choroid tissue
What is the total refractive power of the eye
60 diopters
What is the approximate refractive power of the cornea
40 diopters
What is the approximate refractive power of the crystalline lens
20 diopters
VID
Visible Iris Diameter
Average is 10.6
HVID
Horizontal Visible Iris Diameter
Average 11.7m
SEAL
Superior Epithelial Arcuate Lesion
Thin arced lesion in the upper part of cornea between “10 & 2 O’clock”
What is the radius of curvature of the front of the cornea
7.7mm
What is the radius of curvature of the back of the cornea
6.8mm
The______is aspheric and elliptical in shape
Cornea
What is the central thickness of the cornea
0.5mm
What is the edge thickness of the cornea
1.0 mm
Epithelium
Outermost layer of the cornea. It is the layer exposed to the tear film. About 10% of total corneal thickness. Highly regenerative, mild corneal abrasion’s are often completely healed within 24 hours
Bowman’s membrane
Second layer of the cornea. Essentially a modification of the underlying stroma. Unlike the epithelium it will not regenerate if scratched or damaged
Stroma
Approximately 90% of the corneal thickness. 200 to 250 layers of cells which light parallel to the corneal surface. Does not regenerate.
Decemet’s membrane
A strong structureless layer which is secreted by the endothelium. Elastic and resistant to trauma and pathology
Endothelium
Innermost layer of the cornea consisting of a single layer of flattened cells. Very susceptible to trauma and pathology. Provides deturgecence to cornea
Greek word for rainbow
Iris
Deturgence
The normal state of partial dehydration in the cornea
What is the pH of the human tear
7.4
What is the purpose of the iris
To control light levels inside the eye by expanding and contracting the pupil.
What muscles in the iris expand the pupil
dilator muscles
What muscles in the iris contract the pupil
sphincter muscles
Aniridia
absence of the iris from the eye
Ocular Albinism
no pigment (melanin) in the iris
Iridocyclitis
inflammation of iris and ciliary body
Rubeosis
growth of abnormal blood vessels in iris
Uveitis
blanket term for any inflammation of the iris, ciliary body or choroids
Aniscoria
pupil sizes are different in each eye
Miosis
when the pupil constricts
Mydriasis
when the pupils dilate
Miotic drops
cause the pupil to constrict
Mydratic drops
cause the pupil to dilate
The crystalline lens is ____ in shape
biconvex
Cataract
a cloudy opacity in the crystalline lens
The _____ _____ causes a blind spot in vision that most people do not notice because of the overlap of vision from both eyes
optic nerve
A Snellen Chart
is used to determine visual acuity
20/20 means
the patient can see an object at 20 feet that a normally sighted person can also see at 20 feet
A larger number at the bottom of visual acuity means
worse vision (20/40, 20/70 etc)
A smaller number at the bottom of visual acuity
Better than normal vision (20/15, 20/10)
What are the layers of the tear film
Lipid, Aqueous (Lacrimal), and Mucoid layer
Lipid Layer
fatter material produced by meibomian glands, top layer of tear film. Primary function to prevent rapid evaporation of tears
Mucoid layer
Innermost layer of tear film, lays immediately against corneal and conjunctival epithelial cells. Converts the epithelium, which is naturally hydrophobic into a hydrophilic surface.
Aqueous layer
Also called Lacrimal layer. mostly water, provides moisture, nutrients and oxygen to the cornea
What is the index of refraction of tears
1.3375
Puncta
drain tears from eye with each blink by the force of lids closing
Schirmers Test
Tests quantity of tears produced in dry eye patients. Strips of paper are placed in eyes for 5 minutes then wetness is measured. Should be about 15mm of wetness
Rose-Bengal
a purplish stain used to assess integrity of cornea. Colors any dead or regenerating cells on epithelium as brown spots when viewed under a green filter (slit lamp)
BUT Test
Break Up Time
How long tears take to start evaporating between blinks. 10-12 seconds is normal. Less than 7-10 can cause problems for contact lens wearers
What is the wavelength of the Visible Spectrum of Light
370-750 nanometers
What is the wavelength of short ultraviolet light
200-295 nanometers
What is the wavelength of long ultraviolet light
296-400
What is the wavelength of short infrared light
750-1400 nanometers
What is the wavelength of UV C
200-290 nm
What is the wavelength of UV B
290-320nm
What is the wavelength of UV A
320-400nm
UV C is
Extremely dangerous, but is absorbed completely by the ozone layer. However is is also emitted by welders torches
UV B causes
sunburn, corneal burns, retinal damage. Over time, causes cataracts. Mainly absorbed by cornea and partly by crystalline lens.
Exposure to UV B increases by ___with every___
10%
1000 feet of elevation
UV A causes
Suntans, skin aging and contributes to cataracts. Primarily absorbed by crystalline lens
What is the visible spectrum of light from longest waves to shortest waves
Red, Orange, Yellow, Green, Blue, Indigo, Violet
Index of refraction can be determined by what formula
Speed of light in air (186,000 miles per second) by speed of light in a given material
Angle of Incidence
the angle at which incoming rays of light strike the surface of an object
Angle of Reflection
predictable angle of light bouncing off a reflective surface
Snells Law
formula used to calculate angle of refraction in a medium with a known index of refraction
Angle of Refraction
angle of light bending inside a medium
Spherical Abberation
when parallel light rays enter a large area of a spherical lens surface, the peripheral rays focus sooner than the central rays and cause blurring of the image.
What “shape” of distortion do strong plus lenses have
pincushion (inward curvature)
What “shape” of distortion do strong minus lenses have
Barrel (outward bulging)
Vogel’s rule for Plus lenses
Best base curve is found by adding sphere power (or spherical equivalent) to +6.00
Vogel’s rule for minus lenses
Best base curve is found by adding half the sphere (or spherical equivalent) to +6.00
If a patient comes in complaining that the new glasses make everything smaller, but the rx and all parameters are the same as the old pair…
the base curve was made flatter than the original
If a patient comes in complaining that the new glasses make everything larger but the rx and all parameters match the old pair…
the base curve was made steeper than the original
Meniscus lens
a lens with a convex front surface and concave back surface. Nearly all lenses made today are this shape
Hard Designed PALs
have a wider distance and near area. Most of the “edge blur” is to the sides of the intermediate area
Soft Designed PAL’s
distribute the edge blur from the center towards the distance and near so the intermediate area is wider
Equithinning
Prism thinning on PALs. Base down prism ground equally into a set of PALs to reduce thickness difference between top and bottom portions of the lens
Lenticular Lens
for patients with high rx’s. a center “disc” with all the rx is mounted into a carrier lens with little to no power. Reduces weight and thickness and aids in mounting of lens in a frame for eyeglasses
An object viewed through a prism from one meter a way is displaced one centimeter. What is the power of the prism
one diopter
Prism power formula
centimeters(displaced)/meters(distance away)
Object displaced 1cm at 0.5meter: 1/0.5= 2 diopters of prism
Formula for finding power from focal length
1/Focal length=diopters of power
Formula for focal length
1/power in diopters= focal length
The Stronger the power the ____ the focal length
shorter
The weaker the power the ___ the focal length
longer
Rule of thumb for effective power of a lens
a 10.00 diopter lens moved 5mm will change by 5 diopters.
base out prism on a plus lens is moved
towards the temples
base in prism on a plus lens is moved
towards the nose
base up prism in a plus lens is moved
up
base down prism in a plus lens is moved
down
base out prism in a minus lens is moved
towards the nose (in)
base in prism on a minus lens is moved
towards the temples (out)
base up prism on a minus lens is moved
down
base down prism on a minus lens is moved
up
Cancelling prism directions
Both lenses have base up, both lenses have base down or one lens has base in and one has base out
If a set of lenses has 2 diopters BI on the OD and 4 diopters BO on OS how much prism is there
2 diopters BO on OS
The 4D OS cancels out the 2D OD, leaving another 2D in the OS leftover
Compounding prism directions
Both lenses have base in, both lenses have base out, or One has base up and one has base down.
If a pair of lenses have 2D BO in OD and 4D BO in OS how much prism is there
6D BO OU
How to find horizontal prism in a lens with astigmatism
find power in 180 meridian, then use prentice rule
How to find vertical prism in a lens with astigmatism
find power in the 90 meridian then use prentice rule
How many mms below the pupil should optical centers be measured for (how many) degrees of pantoscopic tilt
One mm below the pupil for every two degrees of tilt
How to calculate slab off for anisemetropia
find power at 90 (issue is at reading/vertical level) use prentice rule using how many mm patient looks below OC to read as decentration, then grind the base up prism into the most minus/least plus powered lens (accounting for compounding/cancelling prism amounts)
Image Jump
caused by patient looking under the segment line for reading, going from distance OC to reading OC, causing prism.
Calculate Image Jump using prentice rule
Use add power and near OC
Rx is +2.00 OU and +2.00 add power. Near OC is 5mm below segment line
5X2=10/10= 1 diopter image jump
Most commonly used metal for making frames
monel
An oval face should wear
can wear just about any frame shape
An oblong face should wear
deep frames with low temple attachments. wider oval shaped frames
round faces should wear
narrow frames with high temple attachments. rectangular frames
square frames should wear
narrow frames with high temple attachments, oval shapes with more width than depth
triangular (wide jaw, narrow forehead) faces should wear
darker colors. frame width should equal widest part of lower face. cat eye shapes
diamond shaped (narrow forehead, wide cheeks narrow jaw) faces should wear
lighter colors, use frames with distinctive browlines, rimless styles, ovals and cat eyes
Triangular faces with wide forehead and narrow narrow jaw should wear
light colors, wide bottomed frames, rimless styles
patients with narrow pds benefit cosmetically from
lighter colored bridges on frames
patients with wide pds benefit cosmetically from
darker bridges on frames
to shorten a long nose
use a low set or dark bridge
to lengthen a short nose
use a clear or high set bridge
Refractive Astigmatism
Sum of any corneal and lenticular (internal) astigmatism in the eye. Amount of astigmatism in the spectacle Rx. Found during the refraction.
Corneal astigmatism
most common form of astigmatism. Any astigmatism found on cornea. Determined using the difference between K-readings
Lenticular astigmatism
astigmatism found in the internal structures of the eye. It is the difference between the Refracted Astigmatism and any Corneal Astigmatism found in the K readings
How much astigmatism is usually required to be corrected by a toric lens
more than 0.75 diopters
What is “With the Rule” astigmatism
when the horizontal (180 or about) meridian is flatter than the vertical (90 or about) meridian
What is “Against the Rule” astigmatism
when the horizontal (at 180 or about) meridian is steeper than the vertical(90 or about) meridian
What is “Oblique” astigmatism
When the horizontal meridian is closer to 45 degrees and the vertical meridian is closer to 135 degrees
What is Residual Astigmatism
Any leftover astigmatism found during an over refraction while wearing contact lenses
True or False
Spherical GP lenses can compensate for both corneal and lenticular astigmatism
False. They’re great at neutralizing corneal astigmatism (using tear lens) but cannot compensate for any lenticular astigmatism. Toric soft lenses would be best
Are GP or Soft lenses better for against the rule astigmatism
soft, due to the way the drape the cornea
A spherical GP lens is best used to correct for how much _____ astigmatism
Less than 2.5-3D of corneal, with the rule astigmatism
Toric GP lenses should be used when
there is more than 3D of corneal astigmatism, when there is against the rule astigmatism, or to correct for lenticular astigmatism
What other names is the base curve of contacts known as
Base Curve Radius (BCR)
Back Optic Zone Radius (BOZR)
Back Central Optical Radius (BCOR)
The base curve of a contact lens can be
spherical or aspheric
Aspheric contact lenses are specified by
E-Value
larger E-Value indicates a greater rate of flattening or lengthening from lens center to edge
An E-Value on a contact lens means
a spherical base curve
An E-Value from 0-1 are ___ curves
elliptical
An E-Value of 1 is a ____ curve
parabolic
