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Strabismus 106 > Visual Acuity > Flashcards

Visual Acuity Flashcards

1
Q

What is VA?

A

Ability of the individual to discriminate detail; to resolve a pattern into spatially separated elements.

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2
Q

What is visual resolution?

A

Denotes size of detail able to be resolved by the individual

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3
Q

What can 4mo’s do with regards to VA?

A

They like black-&-white gratings, prefer patterns, fix & follow light and are able to ask parents about the child.

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4
Q

What questions should you ask parents with regards to their 4mo’s VA?

A

Whether the child:
- Makes eye contact
- Responds to facial expression
- Responds to lights going on/off
- Whether pupils respond to light
- Responds to objects moving

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5
Q

What VA test should you use for a 4mo?

A

Forced-Choice Preferential Looking; Keeler/Teller or Lea Gratings Paddles

Black and White gratings have a number of cycles per degree at the nodal point of the eye. The narrower they are the higher the spatial frequency.

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6
Q

How do you use Keeler or Teller acuity cards?

A

For 8wks -12mo
15 cards of B-&-W gratings either L or R with 1 blank and a 4mm central hole. They range from 0.32 to 38 c/degree.

Held at 38cm using a staircase method moving up 0.5, 1 or 2 octaves depending on infant response.
1 Octave = 0.22 or 0.44 c/degree
0.5 Octave = 0.22 or 0.33 c/degree

If 2x wrong = not seen
Show lower card
If losing interest can twist cards to show vertically

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7
Q

How far do you hold Keeler/Teller cards?

A

38cm

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8
Q

What range do the c/degree are Keeler/Teller cards?

A

0.32 up to 38 c/degree

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9
Q

What age-range are Keeler/Teller Acuity Cards for?

A

8wks - 12 mo or people with mental or physical disabilities

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10
Q

What distance are Lea Gratings Paddles held at?

A

57cm or can be at 29cm & 86cm

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11
Q

What are Lea Gratings Paddles?

A

Black-&-white stripes of 4 paddles 8” in diameter measured in cycles per centimetre (cpcm) at 0.25, 0.5, 1, 4 and 8.
They watch the eyes to see if moving towards the striped or blank paddle or not.

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12
Q

Why are Lea Gratings Paddles good?

A
  • Good for ages up to 12mo
  • Portable
  • Good for individuals with disabilities
  • Fast to perform
  • Better fixation for under 12mo compared to Cardiff Cards
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13
Q

What age-range are the Cardiff Acuity Cards for?

A

1.5 year olds to around 2.5 years

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14
Q

What are the Cardiff Acuity cards?

A

For testing visual acuity in 1.5 - 2.5yo

They’re grey cards with a familiar pic for the age range e.g. fish. The picture has a white band bordered by 2 black bands of half the width.
The average luminance is equal to the grey backgrounds and thus is a vanishing optotype and so beyond the acuity threshold it is invisible.
The pic is at the top or bottom and there are 3 cards per acuity level with 11 levels in total.

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15
Q

How many cards and levels are there in the Cardiff Acuity Cards?

A

The pic is at the top or bottom and there are 3 cards per acuity level with 11 levels in total.

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16
Q

What VA do we test holding the Cardiff Acuity cards at 1 meter?

A

6/60 - 6/6

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17
Q

What VA do we test holding the Cardiff Acuity cards at 0.5 meters?

A

6/120 - 6/12

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18
Q

How do you carry out the Cardiff Acuity Cards?

A
  • Occlude 1 eye, beginning with the widest target (lowest acuity)
  • Watch eye movements
  • 2 out of 3 correct you’d move to the next level in a staircase procedure
  • If incorrect = use a larger target
  • The orthoptist is blind to the direction and they must watch the eye movement to see if it was towards the image or not

Able to talk to a patient, name a picture and encourage pointing.

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19
Q

At what age would you use Kay Pictures?

A

At 2 - 4 years old

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20
Q

What are the Kay Pictures?

A

For 2.5yo’s and over. The are based on the principle of the Snellen test where line width on Snellen letters is equal to the lines on Kay pictures. They’re single pictures that reduce in size in a flip-book. Have a matching key card.

The sizes range from 1.0 to -0.1 at 3m. There are 8 pictures in groups of 4 (except at 1.0 and 0.9 where there are 2)

Crowded and uncrowded versions. Single is 1.0 to 0.00.

New pictures chosen by 420 children as the most easily recognised

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21
Q

What distance should we hold Kay Pictures?

A

At either 3m or 6m

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22
Q

Which VA test for children is based on Snellen?

A

Kay Pictures

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23
Q

What VA range does Kay Pictures test?

A

The sizes range from 1.0 to -0.1 at 3m. There are 8 pictures in groups of 4 (except at 1.0 and 0.9 where there are 2)

Crowded and uncrowded versions. Single is 1.0 to 0.00.

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24
Q

What are there other tests for VA for 2+ year old’s?

A

Lea Symbols & Landolt C or E Charts

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25
Q

What is Lea Symbols?

A

A VA test for 2+ year olds that’s used worldwide and developed in Finland. It’s based on LogMAR and decreases by 0.1 with VA between 2.0 and 0.1 at a distance of 3m. has both single and crowded options.

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26
Q

What is Landolt C or E Charts?

A

A VA test for 2+ year olds that have C’s or E’s presented in 4 directions and the patient has to indicate the direction. Is at 6m and is based on a 5x5 grid pattern and is often used in individuals with high illiteracy rates

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27
Q

What do you do if a baby has very poor VA?

A
  • See if they can fix and follow bright toys/lights.
  • Use an OKN drum (optokinetic) and watch eyes move
  • See if light can be followed in a dark room
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28
Q

What do you do if a child or adult has very poor VA?

A
  • Move closer with the logMAR chart
  • See if they can count fingers and if not see if they can do hand movements or perception of light
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29
Q

What are the limits of VA?

A

Optical factors like the ‘diffraction phenomenon’ or neural factors such as anatomical structure of retinal photoreceptors, pupil size, optical aberrations or region of retina stimulated

Light spread on the retinal image is dependent on pupil size with rays on the periphery being more aberrated (blurred)

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30
Q

What is the ‘diffraction phenomenon’?

A

A limitation to VA. When an emmetropic eye in optimal focus make a blurred circular patch surrounded by faint rings a

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31
Q

When it comes to VA, what is ‘minimum visible’?

A

The ability to perceive presence of single target e.g. face

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32
Q

When it comes to VA, what is ‘minimum detectable/distinguishable’?

A

The ability to identify features or internal arrangements in visible target e.g. eyes or nose

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33
Q

When it comes to VA, what is ‘minimum separable’?

A

The ability to detect separate spatial separation between adjacent lines with black-&-white grating tests in forced-choice preferential looking (FCPL)

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34
Q

When it comes to VA, what is ‘hyperacuity’?

A

The ability to perceive alignment and orientation of linear stimuli e.g. see straight and diagonal directions which is often used in research

35
Q

When it comes to VA, what is ‘minimum recognisable’?

A

Ability to determine smallest optotypes based on Snellen and LogMAR principles

36
Q

What’s the conversion of LogMAR to Snellen from 1.0 to -0.3?

A

6/60 = 1.0
6/48 = 0.9
6/38 = 0.8
6/30 = 0.7
6/24 = 0.6
6/19 = 0.5
6/15 = 0.4
6/12 = 0.3
6/9.5 = 0.2
6/7.5 = 0.1
6/6 = 0.0
6/4.8 = -0.1
6/3.8 = -0.2
6/2 = -0.3

37
Q

How does the Snellen Chart work?

A

Visual angle subtended at nodal point of the eye by altering size of component parts of a letter. Detail subtends a visual angle of 1 minute of arc

38
Q

What is the numerator and denominator of a Snellen number?

A

Test distance over distance each component of letter subtends 1’ arc at the nodal point

39
Q

How many minutes of arc does a whole Snellen Letter subtend at at the nodal point?

A

5’

40
Q

How do you work out the size of a 6/36, 6/24 or 6/12 letter?

A

We know the number of arc e.g. 36 divided by 6 = 6 and then times that by 5 (minutes of arc) so is 30mm
in 6/24 it’s 4, 4 x 5” = 20mm
and 6/12 it’s 2, 2 x 5” = 10mm

41
Q

How do you read a Snellen Chart?

A

if 2 letters wrong we do -2 at the end, if +1 we do 1 from the line below and pt means half of the line. If 3 wrong then ignore that line.

42
Q

What does logMAR stand for?

A

Logarithm of the Minimum Angle of Resolution

43
Q

What is MAR?

A

It’s the Minimum Angle of Resolution. It is the minimum angle subtended by each unit of the letter (the angular size of detail within the optotype at threshold). It’s usually 1/5 letter height.

44
Q

Who designed logMAR?

A

Bailey & Lovie (1976)

45
Q

What is the gold standard test for logMAR?

A

ETDRS (Early Treatment Diabetic Retinopathy Study)

46
Q

How many letters are on a logMAR chart?

A

5 with proportional spacing in a consistent ratio of size progression with the approximate equal length of letters at each size level

47
Q

On a logMAR what is each letter worth? and each line?

A

0.02 per letter making 0.1 per line

48
Q

What distance should Bailey-Lovie be at? and what letters are it based on?

A

6m; based on British standard letters

49
Q

What distance should ETDRS be at? and what letters are it based on?

A

4m or 3m; based on Sloan letters

50
Q

Whats the termination rule for logMAR?

A

If able to read 3 on 1 line then you can move onto the next line (0.02 x no. of letters incorrect)

51
Q

What’s the crowded logMAR acuity test also known as?

A

Glasgow Acuity Test

52
Q

How is the crowded logMAR organised?

A

4 letters (0.025 in a crowding bar) for the uncrowded it’s 2 letters per acuity level which is for pre-school and 3-5yo’s at 3m

53
Q

What does the Sonksen logMAR test look like?

A

UCL. Similar to the crowded logMAR with 2 flip-over and 4 surrounded by crowding bar. Tested at 3m and has a near test chart. The letters are easiest for young children to match.

54
Q

What age should the crowded logMAR be used for?

A

Pre-School & 3-5yo’s held at 3m

55
Q

What are the 2 types of Near VA tests?

A

1) Typeset Material - similar to print in newspaper, sentences, paragraphs or words and not comparable to distance VA tests
Called “N” test types being Moorfields for adults and Maclure for children

2) Comparable to distance chart
e.g. reduced snellen, logmar, near single or crowded Kay, Lea symbols, Single S.G. and Landolt

56
Q

How can you tell if a chart is ETDRS or Bailey-Lovie?

A

ETDRS has Snellen and LogMAR equivalents on the right
Bailey-Lovie is logMAR so has this on the right and meters on the left

57
Q

What colour books are the crowded and uncrowded LogMAR in?

A

Crowded - Blue & Red
Uncrowded - Yellow

58
Q

For 1 prism dioptre, how many degrees are there?

A

0.57

59
Q

For 1 degree, how many prism dioptres are there?

A

1.75

60
Q

What must we consider when selecting VA tests?

A
  • Age
  • Co-operation (any disabilities?)
  • Testing Distance
  • Principle of Test (e.g. gratings, logMAR, crowded)
  • Level of VA
  • Presence of Amblyopia
61
Q

What VA tests are at 33cm?

A
  • Snellen
  • Single & Crowded Kays
  • Moorfields
  • Maclure
  • N test type
  • logMAR tests (40cm)
62
Q

What VA tests are at 38cm?

A

FCPL

63
Q

What VA tests are at 50cm or 1m?

A

Cardiff Cards

64
Q

What VA tests are at 3m?

A
  • Single/ Crowded Kays
  • Crowded & Uncrowded LogMAR
  • Sonksen
  • Lea symbols
65
Q

What VA tests are at 4m?

A

logMAR charts

66
Q

What VA tests are at 6m?

A
  • Snellen
  • logMAR
  • Kay Pictures
67
Q

What are the advantages of Preferential Looking?

A
  • Can test younger children
  • Some are portable (Lea paddles)
  • Numerical value
  • Close so likely to retain attention
68
Q

What are some disadvantages of Preferential Looking?

A
  • Less accurate, can overestimate VA as crude measurement
  • Cannot test for amblyopia
69
Q

What are the advantages of Cardiff Acuity Cards?

A
  • Can test younger patients
  • Vanishing Optotypes
  • Portable
  • Close to child (1m and 0.5m)
  • Familiar pictures to children
70
Q

What are the disadvantages of Cardiff Acuity cards?

A
  • Less accurate (overestimates VA)
  • Cannot test for amblyopia
  • Dull colour = loss of interest
  • Practice required from orthoptist
71
Q

What are the advantages of Single Kay Pictures?

A
  • More accurate as subjective, 3m away, crowding bar
  • Simple, familiar pictures
  • Portable
72
Q

What are the disadvantages of Single Kay Pictures?

A
  • Cannot test for amblyopia as no crowding phenomenon
  • Overestimates VA in comparison to crowded
73
Q

What did Howard & Firth (2006) find about the Cardiff Acuity Cards?

A

In 4-9yo without spectacle correction Cardiff acuity cards under-diagnosed reduced visual acuity caused by refractive error in 44% of the children compared to the Bailey-Lovie logMAR chart

74
Q

How does our VA change from 3-7yo?

A

3 years = 0.18 or 0.19
4 years = 0.05
5 years = -0.05
6 years = -0.100
7 years = -0.130 (approx)

75
Q

What did Elliot & Firth (2009) find about crowded Kay and crowded logMAR in amblyopes?

A

Crowded logMAR (letter-based test) is better to detect severe/moderate amblyopia compared to Crowded Kays (picture-based test)

76
Q

When would we use functional vision assessment?

A

They’re graded targets and toys. Disabilities such as global developmental delay so do a functional vision assessment.

77
Q

What is the Bradford Visual Function Box (BVFB)?

A

A Functional Vision Assessment use to assess visual function in children with complex disabilities

78
Q

What are some computerised VA tests?

A
  • COMPlog acuity chart
  • Test Chart Xpert –Thomson software
  • EVA – electronic visual acuity tester
  • Kays iSight Pro– App for iPad/ mobile phones http://isighttest.com/index.html
79
Q

What are the advantages of computerised VA tests?

A
  • Controlled and standardised
  • Randomised letter presentation
  • Testing distance can be varied
  • Automated score calculation – minimise examiner bias, can use technicians instead of orthoptists
  • Present single or row of letters with crowding bar
80
Q

What are the disadvantages of computerised VA testing?

A

At poorer VA levels there’s less than 5 letters presented on the screen

81
Q

How should VA be recorded? Give an example

A

VA cgls R 0.05(1) L 0.10(2) LogMAR crowded at 3m

VA sgls R 6/6(2) L 6/15(1) Cardiff Cards at 1m

VA sgls BEO 3.8(1) R 2.1(2) L 1.4(3) c/deg FCPL at 38cm
(equal objection to occlusion of EE, feed up when examined left eye, suggest test left eye first at next visit)

82
Q

What’s the termination rule in recording logMAR?

A

Cut off point is being able to read 3 on 1 line - go on to check the next line

83
Q

What tests would you perform in babies with very poor VA?

A
  • Fix and follow bright toys/light
  • OKN drum
  • Present a light in a darkened room
  • Pupils reacting to light
84
Q

What tests would you perform in children or adults with very poor VA?

A
  • Alter testing distance
  • Counting fingers (CF)
  • Hand movements (HM)
  • Perception of light (PL - cover one eye and then get them to put their finger over the light)

Strabismus 106 (35 decks)

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