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PPO > Visual Acuity > Flashcards

Visual Acuity Flashcards

1
Q

What is visual acuity

A

the spatial resolving capacity of the visual system

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2
Q

what is clinical visual acuity

A

the measure of the ability of a patient to resolve fine detail

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3
Q

What is normal VA limited by

A

the anatomy of the eye

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4
Q

what are some factors that limit the eye

A
  1. density of the photoreceptors in the retina
  2. diffraction of the eye
  3. the eye’s optical aberrations
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5
Q

why is VA testing special

A

it is the only test done on every patient every time you see him or her

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6
Q

what are some important reasons you must take VA

A
  1. legal
  2. evaluation of visual function
  3. detection of visual impariment. low vision
  4. detection and monitoring of amblyopia
  5. estimation of refractive error
  6. detection and diagnosis of disease and necessity of intervention
  7. monitoring disease
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7
Q

what is legal blindness

A

the best corrected visual actuity of 20/200 or less in the better eye, or a visual field of no more than 20 degrees

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8
Q

what must you get for a full license in MA in ur VA

A

20/40 in best corrected VA in better seeing eye

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9
Q

what number is the snellen VA chart based on

A

1 min or arc

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10
Q

what does seeing 1 min arc mean

A

seeing 20/20

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11
Q

what is 1 degree equal to in min arc

A

60 min arc

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12
Q

what is 1 min arc equal to in sec arc

A

60 sec arc

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13
Q

what is 1 degree equal to in sec arc

A

3600 sec arc

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14
Q

what is the distance to the fovea to the optic nerve

A

15 degrees

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15
Q

what is the visual pathway

A

light, tear film, cornea, anterior chamber, pupil, lens, vitreous, retina, photorecptors

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16
Q

where does the eye have the highest resolution ability

A

fovea, center of macula

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17
Q

what are the optical limits to normal VA

A
  1. obtical aberrations

2. diffraction

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18
Q

what does a large pupil mean for aberrations and diffraction

A

lower diffraction, more aberrations

-allows more light to retina to reduce diffraction, so resultion limit is aberrations

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19
Q

what does a small pupil mean for aberrations and diffraction

A

reduced optical aberrations, resolution is limited

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20
Q

what is the optimal pupil size

A

3mm

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21
Q

what are the neural limits to VA

A
  1. photorecptor density and packing
  2. light/dark adaptations
  3. other neuronal processes
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22
Q

what is predominatnly found in the macular

A

cones

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23
Q

what are the only photoreceptors found in the fovea

A

cones

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24
Q

where are rods found

A

throughout the peripheral retina

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25
Q

where are rods most concentrated at

A

20 degrees from the fovea

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26
Q

where are cones found

A

macula and fovea (central retina)

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27
Q

what part of the eye has the highest density of photorecptors and the highest visual resolution

A

central retina

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28
Q

what is the cones at fovea theoretical limit to resolution

A

30 sec arc

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29
Q

what is the minimum resolvable letter stroke width that corresponds to snellen va of 20/10

A

0.5 min arc

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30
Q

what are the 3 conditions of vision depending on light

A
  1. photopic vision
  2. scotopic vision
  3. mesopic vision
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31
Q

what condition is the bright light conditions with the best VA

A

photopic

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32
Q

waht is photopic vision mediated by

A

cones

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33
Q

what is dim light conditions, night vision.

A

scotopic

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34
Q

what condition has the poorest sensitivity to dim light

A

photopic

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35
Q

what condition has the highest sensitivity for detection of a spot of light

A

scotopic

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36
Q

what is scotopic mediated by

A

rods

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37
Q

what is the sensitivity factor that the visual system alters it to see under scotopic and photopic conditions

A

a factor of >x10^8

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38
Q

how does the eye alter its sensitivity factor to light

A
  1. change pupil size
  2. fast regeneration of photopigment
  3. other neural processes
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39
Q

out of cones and rods which takes longer to adapt to dim light conditions

A

rods (30-50 min) while cones (5-10 min)

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40
Q

at the macula, waht is the ration between cones synapsing to 1 bipolar/ganglion cell

A

1:1

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41
Q

at the retinal periphery, what is the ration of rods to bipolar cells

A

many rods : 1 bipolar cell

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42
Q

what do the photoreceptors synapse with

A

bipolar and hoizontal cells

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43
Q

what do the bipolar cells synapse with

A

amacrine and ganglion cells

44
Q

where do the ganglion cells exit through

A

optic nerve

45
Q

where is the blind spot

A

15 degrees temporal from fovea

46
Q

what are the layers of the eye

A

retina, choroid, sclera

47
Q

waht is the type of acuity used to resolve 2 objets as separate? ex. grating acuity, landolt c

A

resolution acuity

48
Q

waht is the acuity used to measure the sensitivity of the eye. what’s the smallest object you can see?

A

minimum detectable acuity

49
Q

what the the minimum detectable misalignment. ex. vernier acuity

A

hyperacuity

50
Q

what is the smallest obj that you can identiy and name? used in most clinical charts

A

recognition acuity

51
Q

how is threshold related to sensitivity

A

threshold=1/sensitivity

52
Q

What is the chart:

  • strong serif
  • height x5 detail
  • based on detail (MAR) of 1 min of arc
  • standard dist 20 ft
A

Snellen (1862)

53
Q

what did sloan propose

A

m-unit

54
Q

what is this chart:

  • bailey lovie layout
  • logMAR spacing
  • sloan optotypes
  • standard sit 4m
A

current standard

-ETDRS

55
Q

What are the advantages to hand held charts

A
  • cheap
  • readily available
  • portable
  • free space testing
  • more realistic
56
Q

what are the disadvantages to hand held charts

A
  • variations in contrast and illumination
  • fade w/ time
  • size calibration
  • limited optotoes
  • need to be used at a std distance
57
Q

what type of chart is an etdrs chart

A

back illuminated printed chart

58
Q

what are the advantages to a chart projected onto a screen

A
  • can present multiple optotyes

- lower learning effect

59
Q

which chart do we use in pre clinic

A

charts projected on a screen

60
Q

how to design a VA chart? (6)

A
  1. type of optotype
  2. std test viewing distance?
  3. size of optotype
  4. progression btwn lines
  5. spacing btwn optotypes/lines
    f. # of optotypes per line
61
Q

how many cm in an inch

A

2.54

62
Q

what is 20 ft equal to in in

A

6.096m

63
Q

when do you stop the pt from reading on a snellen chart

A

when they get more than half of the ltters on one line wrong

64
Q

what are some disadvantes for snellen

A 
not geometrical proportion
glare
-for va worse than 20/80 there are too few optotypes 
-projector=multiple optotypes
-different spaces=crowding effect
65
Q

what are some advantages for snellen

A

standarized
based on MAR
projector=multiple optotypes
different spaces=crowding effect

66
Q

what is landolt c

A

series of rings with a 1 min arc gap

placed in 1 or 8 positions

67
Q

what is tumbling e

A

pt says which way e is pointing at

-use for illiterate pts or children

68
Q

advantages for logma

A
  • geometrica progession based on the log10 of the critical dtail in min of arc
  • proportional spacing for all levels of VA
69
Q

advantage for etdrs

A

-each line differs from the previous line by a size of 0.1 log

70
Q

what is the std distance for etdrs

A

4m

71
Q

when do you stop the pt from reading for an etdrs chart

A

when they miss 4/5 letters

72
Q

are etdrs or snellen charts shown to have a better VA score

A

etdrs

73
Q

what are some common errors for snellen based chart

A
  1. no proper clear instructions
  2. not observe pt.
  3. not push pt to guess
  4. show one line/letter at a time
74
Q

what must you always remember to record for etdrs charts

A

the sign

75
Q

what is an ico near vision card based on

A

logMAR

sloan letters

76
Q

what is the std distance for ico near vision card

A

40cm or 16 inches

77
Q

what is the standard distance for a runge chart

A

40 cm or 16 in

78
Q

for runge chart when you record..

A

make sure to record the line they got ALL 3 LETTERS CORRECT

79
Q

which value do you use to record for runge chart

A

either snellen equivalent or logmar value

-be sure to record viewing distance

80
Q

what is the formula for recording amplitude of accommadation

A

F=100/d (cm)

81
Q

what line do you have your pt look at to measure amp

A

one line above best near VA

82
Q

what must you round to for amp

A

nearest 0.50 D

83
Q

what is the formula for minimum amp

A

15- (age/4)

84
Q

what metrics do you use for amplitude of accomodation

A

cm

85
Q

at what feet do you do lea cards

A

10 ft

86
Q

which VA do you check for under 4 years old for lea cards

A

20/40 or 10/20

87
Q

which VA do you check for over 4 years old

A

20/36 or 10/16

88
Q

what are we looking for in pediatric screenign

A
  1. amblyopia
  2. eye disease
  3. any condition that may affect school performance
89
Q

what is crowding

A

resolution is impaired by the presence of neighboring ojects

90
Q

who are egger’s chart good to use for

A

myopia and astigmatism

91
Q

what kind of lens do you use to correct for myopia

A

divergent lens

92
Q

what kind of lens do you use to correct for hyperopia

A

convergent lens

93
Q

why is egger’s chart not useful for young hyperopes

A

bc they have compensation of accomadation. must be 45 years or older to use

94
Q

when must you take pinhole

A

when VA less than or equal to 20/30

95
Q

how to measure VA in pt with low vision in etdrs and snellen

A

etdrs @ 4, 2, or 1m

feinbloom (snellen) @ 10 ft or closer

96
Q

what is the std distance for feinbloom

A

10 ft

97
Q

when do you stop in feinbloom

A

when they miss half or more of the letters in a line

98
Q

how to record feinbloom?

A

distance/letter size
ex. VA cc (Feinbloom) OD 10/180 -1
OS 5/700

99
Q

20/20 is equivalent to how many cm and M

A

40cm/.4M or 4m/4M

100
Q

what are factors that could affect VA

A
  1. doctor (knowledge, instructions, confidence)
  2. test
  3. pt (psychological, systemic, ocular)
101
Q

what is differential diagnosis (DDx)

A

questioning what is affecting visual functioning in order to come up w/ the most likely diagnosis

102
Q

inflammation of cornea

A

keratitis

103
Q

inflamattion of anterior part of cornea

A

uvetitis

104
Q

when cornea is not curved, cone like

A

keraoconus

105
Q

imperfections in media, more prominent w/ a large pupil

A

aberrations

106
Q

light interferes w/ itself, more prominent w/ a small pupil

A

diffraction

PPO (14 decks)

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