NCSORB Flashcards
1
Q
Rods number 125 million & are responsible for ____ vision.
A
Night vision, black & white, motion, peripheal
2
Q
Cones number about 6 million & are responsible for ___ perception
A
Day vision, detail, visual acuity, color
3
Q
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?
A
inside nasal edge
4
Q
Glacuoma is caused by an increase in ___ in the eye
A
pressure
5
Q
What does OC stand for
A
optical center
6
Q
The focal point for a minus lens occurs ___ of the lens
A
in front
7
Q
A polarized lens cuts out vertical or horizontal light
A
horizontal
8
Q
What is the thinnest an industrial safety lens should be
A
3 mm
9
Q
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
A
progressive
10
Q
the crystalline lens has a focal power of approx _____ diopters
A
twenty
11
Q
What are the six muscles which allow the eye to move in different directions?
A
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
12
Q
How do you calculate minimum blank size
A
double the decentration & add it to the ED of the frame, then add 2
MBS= ED + (2X Decentration) + 2
13
Q
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
A
68
10+56+2=68
14
Q
What is the standard for measuring spectacle tolerances
A
ANSI Z80.1
15
Q
What year was the Boxing System introduced and by whom?
A
1962
Optical Manufacturers Association
16
Q
which bifocal lens is not a once piece construction: A) plastic round 22 B) flat top 28 glass C) progressive plastic D) glass executive
A
B
flat top 28 glass
17
Q
what is the index of the cornea
A
1.37
18
Q
-3.00 +2.00 x135
is called what
A
compound myopic astigmatism
19
Q
where is the posterior chamber
A
directly behind the iris and in front of the crystalline lens
20
Q
this lens is the least dense available
A) CR-39
B) glass
C) hi-index
D) poly
A
CR-39
21
Q
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
A
B
check base curve face form and tilt
22
Q
What is the index of flint glass
A
1.65
23
Q
How many layers are there in the retina
A
ten
24
Q
-1.00 +3.00 x180
is called what
A
mixed astigmatism
25
A plus lens moved ___ creates base in prism
in
26
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
27
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
28
a ___ lens moved in creates base out prism
minus
29
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
30
light rays passing through a plus lens actually ____
intersect/ converge
31
the limbus of the eye is adjacent to the
cornea
32
what does the "7" in "7X28" trifocal mean
height of the intermediate window
33
What do BU and BD stand for
base up & base down
34
What is the index of PMMA plastic (plexiglass)
1.49
35
a -475 spherical lens decentered 4mm produces
1.9 prism diopters
| (prentice rule: -4.75 * .4= 1.9)
36
blockage of the canal of schlemm produces primarily what
glauoma
37
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)
38
what is the number of major (external) muscles that control eye movement
six
39
what is the index of poly
1.59
40
where is the sclera located
front portion, or "white" of the eye
41
what is the area between the iris/pupil and the cornea called
anterior chamber
42
what is the index of the crystalline lens
1.42
43
bifocal adds are correctly verified when the optican checks the add from which side of the lens against the lens stop
front
44
which lens material is the most impact resistant
poly
45
___ is the absence of the crystalline lens of the eye, if not replaced with an artificial intraocular lens
aphakia
46
when a cataract patient has had an intraocular lens (IOL) inserted they are
pseudophakic
47
the inability to accomodate is
presbyopia
48
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
49
determine the binocular horizontal decentration for the following
Frame PD is 75mm
Patients binocular PD is 69mm
6mm
50
a condition of the cornea in which the cornea asssumes a cone shape is called what
kerataconus
51
what is the minimum height for a FT Trifocal
18mm
52
what are the five layers of the cornea
Epithelium
Bowmans Membrane
Stroma
Descemets Membrane
Endothelium
53
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
54
what is cellulose acetate
plastic/zyl frames
55
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
56
what index is water
1.33
57
the area where the upper and lower eyelids meet, also containing tear ducts is called
canthus
58
the focal length for a plus lens is referred to as ___
postive
59
what does the lens clock do
measures base curve
60
concave surfaces curve what way
inward
61
when fitting a patient with trifocals, what is the usual point of reference for the fitting height
lower pupil margin
62
what metal, used for frames, is strong, resistant to corrosion, and stable under high temperatures
titanium
63
which coating/tint will increase the transmission of light through a lens
anti-reflective
64
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
65
vertex distance is:
the distance from the back/posterior or ocular surface of the lens to the front/anterior surface of the cornea
66
when light rays come to two separate points of focus, one in front of and one behind the retina, it is called
mixed astigmatism
67
the vitreous chamber takes up approx ___ of the eye
2/3
68
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
69
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
70
___ is a drooping of the upper eyelid
ptosis (blepharoptosis)
71
-.50 -0.25x180
| is called what
compound myopic astigmatism
72
a polariscope is used to
measure lens stress (determine if lens has been heat treated)
73
a transparent, gel-like substance that fills the space between the crystalline lens and the retina is called
vitreous humor
74
what is a lens caliper used for
measuring lens thickness
75
the focal point for a plus lens occurs ___ the lens
behind
76
what is the reticle center of a lensometer used for
reading lens power
77
the line drawn directly across a lens shape at the 180 line is called
datum line
78
the tissue membrane lining the inside back of the eye, which contains the sensory receptor cells that collect light energy is called what
retina
79
determine the vertical decentration
B= 51
Patients OC 32 mm
6.5 mm up
80
a minus lens moved out creates ___ prism
base in
81
what muscles dialate in dim light
dialator
82
prism is
a wedge shaped piece of optical medium with a base and an apex. a prism has no focusing power, it deviates light
83
when light rays do not form a single point focused on the retina it is called
astigmatism
84
when light rays come to two separate points of focus, both on the same side of the retina it is called
compound astigmatism
85
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
86
what is the minimum height for a flat top bifocal
11 mm excluding sports relating fitting
87
what is the bony socket that surrounds and protects the eye while providing a structure for attachment of the ocular muscles called
orbit
88
what muscles constrict the pupil in bright light
sphincter
89
phoria is a ____ for the eye to ___ ___ from its normal position
tendency, away from
90
strabismus is commonly known as
crossed eyes
or
squint
91
what is the major refracting body of the eye
cornea
92
what is the densest lens available
poly
93
+100 +200 x090
| is called what
compound hyperoptic astigmatism
94
slab off is grinding away the ___ surface of the lens
back
95
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
96
what does PD stand for
Pupillary distance
97
how many layers are there to the cornea
five
98
a network of nerve fibers that send impulses from the retina to the brain for interpretation as visual images is called what
optic nerve
99
a definite turn of the eye is called
tropia
100
how do you calculate proper base curves for minus lenses
1/2 the spherical equivalent and add +6.00
101
loss of elasticity of the lens leads to what
presbyopia
102
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
103
clouding of the crystalline lens is
a cataract
104
what takes more material than glass to bend the light rays
cr-39
105
on the power drum of a lensometer, which power values are black and which are red
plus is black
| minus is red
106
convex surface curves what way
outward
107
a plus lens moved ___ from the eye gains plus power
away
108
the muscle that controls the amount of incoming light, commonly referred to as 'the colored part of the eye" is
the iris
109
antimetropia means one eye is ___ and the other eye is ____
myopic, hyperopic
110
located directly behind the iris, this lens is ____ in shape
biconvex
111
the three principal parts of the eyes optical system are
cornea, crystalline lens, & retina
112
what is the index of crown glass
1.523
113
the focal length for a minus lens is referred to as
virtual
114
what is the best way to measure for a flat top bifocal
from the lower eyelid
115
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
116
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
117
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
118
what are the three nose pad angles
frontal angle, splay (spread) angle & verticle angle
119
a minus lens moved closer to the eye ___ minus power
gain/increases
120
a plus lens moved out creates ___ prism
base out
121
composed of skin and fleshy tissue, which provide a protective covering for the eye is called what
eyelid (palpebra)
122
plano -100 X045
| is called what
simple myopic astigmatism
123
what is the usual product an optician provides when helping a patient who is being treated for amblyopia
an occulder
124
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
125
when dropball testing a safety lens a ___ inch ball is dropped from ___ inches
1 inch
| 50inches
126
light rays passing through a minus lens have an ___ point of intersection
imaginary
127
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
128
what contains all the sensory receptors for the transmission of light
retina
129
the word that means "double vision" is
diplopia
130
the anterior chamber contains a fluid called what
aqueous humor
131
when light rays come to two different points, both behind the retina it is called
compound hyperopic astigmatism
132
what is the minimum height for a blended bifocal
12mm
| to compensate for the 1-2 mm band of blured vision around the seg
133
where is the retina located
the lining located at the inner backside of the eye
134
what index is air
1.00
135
when a light ray strikes a prism it is deviated toward the ___ but the ___ is displaced toward the ___
base, image, apex
136
when light rays come to two separate points of focus, both in front of the retina it is called
compound myopic astigmatism
137
where is the vitreous chamber located
between the posterior surface of the crystalline lens and the back of the eye
138
What does OU stand for
occli uterque
| both eyes
139
What does OD stand for
occulus dexter
| right eye
140
what does OS stand for
occulus sinister
| left eye
141
the aqueous humor has an index of refraction of
1.33
142
scotoma: detachment of ___ and ___ caused by a sharp blow or injury to the head
rods, cones
143
the white tissue that covers the front surface of the eye which protects and shapes the eye is called
sclera
144
what has up to approx 40 diopters of power
the cornea
145
what do the letters DBL represent
distance between lenses (bridge size)
146
```
which of the following are layers of the cornea:
A) Bowmans Membrane
B) Sclera
C) Stroma
D) Meibomian
```
a & c
| Bowmans Membrane and Stroma
147
what is the index of a high index lens
1.60
148
this lens has more molecules than CR-39 but less than high-index
glass
149
what are the receptors called for the retina
rods and cones
150
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
151
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
152
plano +1.75 x45 is called what
simple hyperoptic astigmatism
153
which portion of the UV spectrum is considered harmful to the eyes
UVA and UVB
154
what type of bridge design makes a long nose appear shorter
low positioned saddle bridge
155
the opening in the iris through which incoming light rays pass is called
pupil
156
which instrument can be used to measure vertex distance
ruler and distometer
157
___ 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
158
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
159
how many inches are in a meter
39.37
160
what is the speed of light
186,000 miles per second
161
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
162
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)
163
what does MRP stand for
major reference point
164
the MRP is located at the OC when...
no prism is prescribed
165
```
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
166
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
167
the standard for sports glasses was developed by
ASTM
| American Society for Testing Materials
168
what factors are considered in computing the power of a thick lens
front curve
back curve
thickness
index
169
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
170
what is a kryptoc
a brand name of round seg bifocals
171
longest vertical dimension of the seg is called
seg depth
172
zylonite is also known as what
cellulose nitrate
| this was banned by the FDA as a frame material due to its flammability
173
the geometric center of a frame is the same as
A + DBL
| GCD is also called Frame PD
174
if a patient has a symmetrical face and a monocular PD of 63/60 what is the monocular near PD
30
175
a glassblowers lens is commonly known as
Didymium lens
| a trade name for special lenses designed to block infrared light from molten glass
176
what are palpebra
eyelids
177
what are conjuctiva
mucus membrane that lines the underside of each eyelid
178
what is an incident ray
the original ray of light that hits a surface or material
179
what is supraversion
both eyes move up
180
what instrument measures the curvature of the center cornea
keratometer
181
how many nanometer is A band ultraviolet light (UVA)
330-400nm
182
what is inset
halfway between distance pd and near pd
183
which UV spectrum is completely absorbed by the atmosphere
UVC
184
what are the three types of plastic bridge types
keyhole, saddle, modified saddle
185
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
186
how many millimeters in an inch
25.4
187
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
188
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)
189
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)
190
how many centimeters in a meter
100
1.0 meter = .01 centimeters
10 cm = 0.10 meter
15 cm = 0.15 meter
etc etc
191
the size of an image will always increase if you
increase base curve
192
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
193
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)
```
194
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)
195
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.)
196
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
197
the law of refraction basically states what
light bends toward the normal when it enters a medium more dense than from which it came
198
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)
199
what is the mechanical center of a lens
the point on the lens surface around which a lens is cut an edged
200
what is the limbus
where the cornea meets the sclera
| (corneoscleral junction)
201
what is LTB
Length To Bend
a measurement for temple lengths
from the center of the hinge barrel to the center of the bend
202
how many diopters is the "1X" power on a microscope
+4.00 diopters
203
what is chromatism
an appearance of colored lights (abnormal coloration)
204
what is the frontalis muscle
brow muscle
| gives the face more expression (raises eyebrows and wrinkles forehead)
205
what is optical infinity
20 ft (6 meters) or more
206
what is asthenopia
eye strain
207
what is the superior lens edge
the top edge of the lens
208
what is isometropia
refractive condition is the same in both eyes
209
what is the canthus
angles formed by the meeting of upper and lower eyelids
210
what is the index of trivex
1.53
211
what is the optic disc
area in the retina where blood vessels and optic nerve exit the eye
212
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
213
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
214
what is ptosis
a drooping of the eyelid caused either by nerve weakness or paralysis
215
what is infraversion
both eyes move down
216
prism cannot be put into a lens with
no power
217
how many nanometers is B band ultraviolet light (UVB)
275-330 nm
218
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
219
what is levoversion
both eyes move left
220
what is dextroversion
both eyes move right
221
how many nanometers is C band ultraviolet light (UVC)
200-275 nm
222
How many nerve fibers are in the optic nerve
1.2 million
223
what is nystagmus
small repetitive involuntary rhythmic side to side or up and down movements of the eye
"shaking of the eyes"
224
what is the inferior lens edge
the bottom edge of the lens
225
what is the annulus of Zinn
ring-like structure at apex of orbit where the four rectal muscles meet
226
what is the lacrimal gland
produces tears, which flow across the eye to lubricate it
227
what is orthophoria
no deviation of the eyes
228
what is a retinoscope
instrument used to examine the refractive error of the eye
229
what is another name for nanometer
millimicron
230
what is a CRP
Corneal Reflection Pupilometer
231
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
232
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
233
what is sagitta
vertex depth
| the depth of the surface curve on a lens measured over a specific diameter
234
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)
```
235
what is scotoma
a blind area of reduced vision in the visual field (detachment of rods and cones)
236
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)
237
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
238
what is amblyopia
loss of vision with out any apparent disease of the eye, usually because of "lazy eye"
239
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
240
a characteristic most CR39 lens series have in common is
minus cylinder form
241
in a minus powered lens light rays ___ and come to a focal point ___ the lens
diverge, in front of
242
fusion occurs in
the brain
243
what is fusion
the power of coordination by which the images received by the two eyes become a single image
244
what controls the amount of light entering the eye
iris
245
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
246
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
```
247
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
248
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%
249
ANSI Z80.1 (2010) add power tolerances are
0-4.00= .12 diopters
| greater than 4.00= .18 diopters
250
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
251
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
252
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
```
253
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
254
How many millimeters in a meter
1000
1mm= 0.001 meter
5mm= 0.005 meter
10mm= 0.01 meter
255
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
256
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
257
what type of lens is convergent
plus lens
258
what type of lens is divergent
minus lens
259
what is tempering
a process of heat treatment to make the lens more impact resistant
260
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.
261
what are the four things that control magnification
the prescription, the front curve, center thickness and vertex distance
262
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
263
what is reverse slab off
base down prism, done on the least minus or most plus lens
264
what is a tonometer
instrument that measures internal pressure of the eye
265
internal (lateral) rectus
moves the eye outwards
266
external (medial) rectus
moves the inwards
267
superior rectus
moves the eye upwards and slightly outward
268
inferior rectus
moves the eye downward and slightly inward
269
superior oblique
moves the eye outward and downward
270
inferior oblique
moves the eye outward and upward
271
If a bifocal has its segments on the _____ of the lens, then the lens must be made in minus cylinder form.
front
272
Light rays that come from ____ feet or more away are considered parallel.
20
273
how many millimeters should the OC be ___ per degree of pantoscopic tilt
.5 (1/2)mm per degree lower
274
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
275
What are symptoms of too much base down prism?
1. 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
2. walls, buildings, and other vertical spaces appear to be taller than they actually are.
3. surfaces seem to slope, so that a sidewalk or hallway seems to be going uphill.
276
what are the symptoms of too much base up prism
1. 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
2. walls, buildings, and other vertical spaces appear to be shorter than they actually are.
3. surfaces see to slope, so that a sidewalk or hallway seems to be going downhill.
277
what is the formula for finding prism
prentice rule
| prism=power * decentration (in centimeters, 2mm= .2cm)
278
what index is the geneva lens measure calibrated to
1.53
279
an uncoated, normal plastic (CR-39) lens will reflect approx what percent of light
8%
92% transmitted
280
when two light waves are "in phase" they will
compound one another
281
what is Tenon's capsule
a layer of tissue that lies between the surface of the eye and the conjunctiva
282
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.
283
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)
284
the point on a lens where the prisms attach either base to base or apex to apex is
the optical center
285
what has the greatest effect on lens magnification
lens power
286
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)
287
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
288
what is the approx dioptric power of the refractive system of the eye
usually between 58 and 62 diopters
289
a bifocal seg that is flat on top and bottom with a depth of 14mm is
ribbon seg
290
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
291
a ___ PD is given as one number
Binocular
| binocular= both eyes together
292
a ___ PD is given as two seperate numbers
monocular
| mono= one
293
the optical cross is a graphic representation used to show the ___ of a lens
meridian powers (total lens power)
294
as pantoscopic angle is increased
the spherical equivalent is increased
295
how do you calculate base curve for plus lenses
spherical equivalent plus +6.00
296
What is the specific gravity of CR-39
1.32
297
What is the ABBE value of CR-39
58
298
What percent of light is reflected from CR-39
4
299
What is the specific gravity of polycarbonate
1.21
300
What is the ABBE value of polycarbonate
29
301
What percent of light is reflected from polycarbonate
5.2
302
What is the index of refraction of trivex
1.53
303
What is the specific gravity of trivex
1.11
304
What is the ABBE value of trivex
46
305
What percent of light is reflected from trivex
4.4
306
What is the specific gravity of crown glass
2.54
307
What is the ABBE value of crown glass
59
308
What percent of light is reflected from crown glass
4.3
309
What is the specific gravity of flint glass
1.62
310
What is the ABBE value of flint glass
50-55
311
ANSI Z80.1 (2010) tolerance for specified base curve is
Plus or minus 0.75 diopters
312
What is the result if fusion cannot occur
Diplopia
313
What word in relation to tropia and phoria means out
Exo
314
What word in relation to tropia and phoria means in
Eso
315
What word in relation to tropia and phoria means up
Hyper
316
What word in relation to tropia and phoria means down
Hypo
317
What is emmetropia
No refractive condition
318
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)
319
What is antimetropia
When one eye is hyperopic and one eye is myopic
320
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.
321
Lazy eye is
Amblyopia (a loss of vision without any apparent disease of the eye)
322
If light comes to focus directly on the retina
Emmetropia
323
If light comes to focus at one point in front of the retina
Simple Myopia
324
If light comes to focus on one point behind the retina
Simple hyperopia
325
If light comes to focus at two points in front of the retina
Compound myopic astigmatism
326
If light comes to focus on two points behind the retina
Compound hyperopic astigmatism
327
If light comes to focus on two points, one in front of the retina and one behind the retina
Mixed astigmatism
328
When light comes to a focus with one point on the retina and one point in front of the retina
Simple myopic astigmatism
329
When light comes to two points of focus, one on the retina and one behind the retina
Simple hyperopic astigmatism
330
A refractive error when light does not focus on the retina
Ametropia
| General term for any refractive error
331
What is the vascular intermediate coat of the eye that furnishes nourishment to the other parts of the eye
Choroid
332
Irregular astigmatism
When the principal meridians in the eye are not 90° apart
333
Regular Astigmatism
When the two principal meridians in the eye are 90° apart
334
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
335
Cilia
Eyelashes
336
Madrosis
Loss of eyelashes
337
Trichasis
Ingrown eyelashes
338
Stye
Purulent inflammation of infected eyelash follicles
339
How many times does the average person blink per minute
7-12 or 12-18 depending on study material
340
How large is the palpebral fissure
15mm high by 30mm wide
341
What is the palpebral fissure
The vertical space between the upper and lower lids
342
What are canthi
The angles formed where the upper and lower lids meet
343
Lateral canthus is where
Towards temples, outer angle of lids
344
Medial canthus is where
Towards nose, inner angle of lids
345
Caruncle
Pinkish part of the eye lid at the medial canthus that houses two accessory tear glands
346
What muscles close the lids
Orbicularis occuli
347
What muscles open the lids
Levator palbebrae superiorus
348
Müller muscle
Gives lids shape
| A weakened muscle causes ptosis
349
Tarsal plates
Stiff tissue that goes over lids from canthus to canthus
350
Palpebral conjunctiva
Transparent mucous membrane the codes the insides of the eyelids
351
Bulbar conjunctiva
Mucous membrane that covers the sclera
352
How far does the upper lid move down during a blink
10-12mm
353
The bottom lid moves up and____during a blink
2-5mm nasally
354
The eyeball it self moves_____ inward in a forced blink and also rotates _____
1-2mm
| Upward
355
What are the folds formed by the junction of the bulbar and palpebral conjunctiva called
Fornix
356
Superior fornix
Folds of conjunctiva behind upper lid
357
Inferior fornix
Folds formed by conjunctiva behind lower lid
358
Limbus
Transition zone between cornea and sclera
359
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)
360
Neovascularization
Caused by long-term corneal edema, the blood vessels from the limbus grow new structures and invade the cornea
361
Hypotonic cornea
More water flows into cornea than out. Occurs when normal evaporation isn't allowed to happen. Cornea is thicker than normal (edema)
362
Isotonic cornea
Equal amounts of water flow in and out of cornea. Cornea is at normal thickness
363
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
364
Zonular fibers
Attached to crystalline lens and ciliary muscles for accommodation
365
Ciliary muscles
Attached to zonular fibers for accommodation
366
Accommodation for distance vision occurs when
The ciliary muscles relax and the zonules contract, thinning the crystalline lens (more minus power in lens)
367
Accommodation for near vision occurs when
The ciliary muscles contract and the zonules relax, thickening the crystalline lens. (More plus power in lens)
368
Retinal detatchment
When the retina tissue pulls away from the choroid tissue
369
What is the total refractive power of the eye
60 diopters
370
What is the approximate refractive power of the cornea
40 diopters
371
What is the approximate refractive power of the crystalline lens
20 diopters
372
VID
Visible Iris Diameter
| Average is 10.6
373
HVID
Horizontal Visible Iris Diameter
| Average 11.7m
374
SEAL
Superior Epithelial Arcuate Lesion
| Thin arced lesion in the upper part of cornea between "10 & 2 O'clock"
375
What is the radius of curvature of the front of the cornea
7.7mm
376
What is the radius of curvature of the back of the cornea
6.8mm
377
The______is aspheric and elliptical in shape
Cornea
378
What is the central thickness of the cornea
0.5mm
379
What is the edge thickness of the cornea
1.0 mm
380
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
381
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
382
Stroma
Approximately 90% of the corneal thickness. 200 to 250 layers of cells which light parallel to the corneal surface. Does not regenerate.
383
Decemet's membrane
A strong structureless layer which is secreted by the endothelium. Elastic and resistant to trauma and pathology
384
Endothelium
Innermost layer of the cornea consisting of a single layer of flattened cells. Very susceptible to trauma and pathology. Provides deturgecence to cornea
385
Greek word for rainbow
Iris
386
Deturgence
The normal state of partial dehydration in the cornea
387
What is the pH of the human tear
7.4
388
What is the purpose of the iris
To control light levels inside the eye by expanding and contracting the pupil.
389
What muscles in the iris expand the pupil
dilator muscles
390
What muscles in the iris contract the pupil
sphincter muscles
391
Aniridia
absence of the iris from the eye
392
Ocular Albinism
no pigment (melanin) in the iris
393
Iridocyclitis
inflammation of iris and ciliary body
394
Rubeosis
growth of abnormal blood vessels in iris
395
Uveitis
blanket term for any inflammation of the iris, ciliary body or choroids
396
Aniscoria
pupil sizes are different in each eye
397
Miosis
when the pupil constricts
398
Mydriasis
when the pupils dilate
399
Miotic drops
cause the pupil to constrict
400
Mydratic drops
cause the pupil to dilate
401
The crystalline lens is ____ in shape
biconvex
402
Cataract
a cloudy opacity in the crystalline lens
403
The _____ _____ causes a blind spot in vision that most people do not notice because of the overlap of vision from both eyes
optic nerve
404
A Snellen Chart
is used to determine visual acuity
405
20/20 means
the patient can see an object at 20 feet that a normally sighted person can also see at 20 feet
406
A larger number at the bottom of visual acuity means
worse vision (20/40, 20/70 etc)
407
A smaller number at the bottom of visual acuity
Better than normal vision (20/15, 20/10)
408
What are the layers of the tear film
Lipid, Aqueous (Lacrimal), and Mucoid layer
409
Lipid Layer
fatter material produced by meibomian glands, top layer of tear film. Primary function to prevent rapid evaporation of tears
410
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.
411
Aqueous layer
Also called Lacrimal layer. mostly water, provides moisture, nutrients and oxygen to the cornea
412
What is the index of refraction of tears
1.3375
413
Puncta
drain tears from eye with each blink by the force of lids closing
414
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
415
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)
416
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
417
What is the wavelength of the Visible Spectrum of Light
370-750 nanometers
418
What is the wavelength of short ultraviolet light
200-295 nanometers
419
What is the wavelength of long ultraviolet light
296-400
420
What is the wavelength of short infrared light
750-1400 nanometers
421
What is the wavelength of UV C
200-290 nm
422
What is the wavelength of UV B
290-320nm
423
What is the wavelength of UV A
320-400nm
424
UV C is
Extremely dangerous, but is absorbed completely by the ozone layer. However is is also emitted by welders torches
425
UV B causes
sunburn, corneal burns, retinal damage. Over time, causes cataracts. Mainly absorbed by cornea and partly by crystalline lens.
426
Exposure to UV B increases by ___with every___
10%
| 1000 feet of elevation
427
UV A causes
Suntans, skin aging and contributes to cataracts. Primarily absorbed by crystalline lens
428
What is the visible spectrum of light from longest waves to shortest waves
Red, Orange, Yellow, Green, Blue, Indigo, Violet
429
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
430
Angle of Incidence
the angle at which incoming rays of light strike the surface of an object
431
Angle of Reflection
predictable angle of light bouncing off a reflective surface
432
Snells Law
formula used to calculate angle of refraction in a medium with a known index of refraction
433
Angle of Refraction
angle of light bending inside a medium
434
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.
435
What "shape" of distortion do strong plus lenses have
pincushion (inward curvature)
436
What "shape" of distortion do strong minus lenses have
Barrel (outward bulging)
437
Vogel's rule for Plus lenses
Best base curve is found by adding sphere power (or spherical equivalent) to +6.00
438
Vogel's rule for minus lenses
Best base curve is found by adding half the sphere (or spherical equivalent) to +6.00
439
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
440
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
441
Meniscus lens
a lens with a convex front surface and concave back surface. Nearly all lenses made today are this shape
442
Hard Designed PALs
have a wider distance and near area. Most of the "edge blur" is to the sides of the intermediate area
443
Soft Designed PAL's
distribute the edge blur from the center towards the distance and near so the intermediate area is wider
444
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
445
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
446
An object viewed through a prism from one meter a way is displaced one centimeter. What is the power of the prism
one diopter
447
Prism power formula
centimeters(displaced)/meters(distance away)
| Object displaced 1cm at 0.5meter: 1/0.5= 2 diopters of prism
448
Formula for finding power from focal length
1/Focal length=diopters of power
449
Formula for focal length
1/power in diopters= focal length
450
The Stronger the power the ____ the focal length
shorter
451
The weaker the power the ___ the focal length
longer
452
Rule of thumb for effective power of a lens
a 10.00 diopter lens moved 5mm will change by 5 diopters.
453
base out prism on a plus lens is moved
towards the temples
454
base in prism on a plus lens is moved
towards the nose
455
base up prism in a plus lens is moved
up
456
base down prism in a plus lens is moved
down
457
base out prism in a minus lens is moved
towards the nose (in)
458
base in prism on a minus lens is moved
towards the temples (out)
459
base up prism on a minus lens is moved
down
460
base down prism on a minus lens is moved
up
461
Cancelling prism directions
Both lenses have base up, both lenses have base down or one lens has base in and one has base out
462
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
463
Compounding prism directions
Both lenses have base in, both lenses have base out, or One has base up and one has base down.
464
If a pair of lenses have 2D BO in OD and 4D BO in OS how much prism is there
6D BO OU
465
How to find horizontal prism in a lens with astigmatism
find power in 180 meridian, then use prentice rule
466
How to find vertical prism in a lens with astigmatism
find power in the 90 meridian then use prentice rule
467
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
468
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)
469
Image Jump
caused by patient looking under the segment line for reading, going from distance OC to reading OC, causing prism.
470
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
471
Most commonly used metal for making frames
monel
472
An oval face should wear
can wear just about any frame shape
473
An oblong face should wear
deep frames with low temple attachments. wider oval shaped frames
474
round faces should wear
narrow frames with high temple attachments. rectangular frames
475
square frames should wear
narrow frames with high temple attachments, oval shapes with more width than depth
476
triangular (wide jaw, narrow forehead) faces should wear
darker colors. frame width should equal widest part of lower face. cat eye shapes
477
diamond shaped (narrow forehead, wide cheeks narrow jaw) faces should wear
lighter colors, use frames with distinctive browlines, rimless styles, ovals and cat eyes
478
Triangular faces with wide forehead and narrow narrow jaw should wear
light colors, wide bottomed frames, rimless styles
479
patients with narrow pds benefit cosmetically from
lighter colored bridges on frames
480
patients with wide pds benefit cosmetically from
darker bridges on frames
481
to shorten a long nose
use a low set or dark bridge
482
to lengthen a short nose
use a clear or high set bridge
483
Refractive Astigmatism
Sum of any corneal and lenticular (internal) astigmatism in the eye. Amount of astigmatism in the spectacle Rx. Found during the refraction.
484
Corneal astigmatism
most common form of astigmatism. Any astigmatism found on cornea. Determined using the difference between K-readings
485
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
486
How much astigmatism is usually required to be corrected by a toric lens
more than 0.75 diopters
487
What is "With the Rule" astigmatism
when the horizontal (180 or about) meridian is flatter than the vertical (90 or about) meridian
488
What is "Against the Rule" astigmatism
when the horizontal (at 180 or about) meridian is steeper than the vertical(90 or about) meridian
489
What is "Oblique" astigmatism
When the horizontal meridian is closer to 45 degrees and the vertical meridian is closer to 135 degrees
490
What is Residual Astigmatism
Any leftover astigmatism found during an over refraction while wearing contact lenses
491
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
492
Are GP or Soft lenses better for against the rule astigmatism
soft, due to the way the drape the cornea
493
A spherical GP lens is best used to correct for how much _____ astigmatism
Less than 2.5-3D of corneal, with the rule astigmatism
494
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
495
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)
496
The base curve of a contact lens can be
spherical or aspheric
497
Aspheric contact lenses are specified by
E-Value
| larger E-Value indicates a greater rate of flattening or lengthening from lens center to edge
498
An E-Value on a contact lens means
a spherical base curve
499
An E-Value from 0-1 are ___ curves
elliptical
500
An E-Value of 1 is a ____ curve
parabolic
