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Investigations > Visual acuity > Flashcards

Visual acuity Flashcards

1
Q

What are 5 stages of assessing visual acuity?

A
  1. check DISTANCE unaided
  2. chest DISTANCE with distance prescription
  3. check DISTANCE with pinhole (if <0.2 logmar, <6/9.5)
  4. check NEAR unaided
  5. check NEAR with near prescription
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2
Q

What are 2 options for distnace vision testing for literate adults?

A
  1. Snellen
  2. Logmar
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3
Q

What are 2 options for near visual acuity testing for literate adults?

A
  1. Test type N chart
  2. Logmar
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4
Q

What are 3 distance visual acuity tests for illiterate adults?

A
  1. Keeler Logmar
  2. Sheridan Gardiner
  3. Kay picture test
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5
Q

What is 1 near visual acuity tests for illiterate adults?

A
  1. Reduced Sheridan Gardiner
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6
Q

What are 3 distance visual acuity tests for children age 3 years and older?

A
  1. LogMAR
  2. Keeler LogMAR
  3. Kay picture test
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7
Q

What are 2 tests for distance visual acuity for children age 2 years and above?

A
  1. Kay picture test (single optotype)
  2. Cardiff cards
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8
Q

What is 1 test that can be used for near visual acuity testing for children 2 years and older?

A

Reduced Kay picture test

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9
Q

What are 3 types of tests which can be used for visual acuity testing in babies/infants?

A
  1. preferential looking tests - Keeler, Teller, cardiff cards
  2. Clinical tests - fixing + following, objection to occlusion, picking up fine objects
  3. Electrodiagnostic tests (EDTs): VEPs, alternating chequerboard of varying frequency
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10
Q

What are 3 preferential looking tests that can be used in babies/infants?

A
  1. Keeler
  2. Teller
  3. Cardiff cards
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11
Q

What are 3 clinical tests of visual acuity in babies/infants?

A
  1. fixing and following
  2. objection to occlusion
  3. picking up fine objects
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12
Q

What are 2 electrodiagnostic tests that can be used for babies/infants VA testing?

A
  1. visual evoked potential (VEP)
  2. response to alternating chequerboard of varying frequency
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13
Q

What distance of arc is subtended by the optotypes (letters) of Snellen charts when read at the distance for the line?

A

5min of arc (each component of letter subtends 1min)

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14
Q

What is normal Snellen acuity in the young eye?

A

1min of arc or 6/6

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15
Q

What may Vernier acuity be up to in the young eye?

A

5s of arc

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16
Q

What change in Snellen acuity should be regarded as significant?

A

change of 2 lines

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17
Q

What is decimal acuity from a Snellen chart?

A

the numerator divided by the denominator - not be confused with LogMAR notation (lower value = better acuity, reverse of decimal notation)

18
Q

What do LogMAR charts record?

A

the logaritm of the minimum angle of resolution

19
Q

What type of chart is the LogMAR chart based on and how many letters are there per row?

A

Bailey-Lovie LogMAR chart - 5

20
Q

Which LogMAR chart is in common usage?

A

Ferris modification, known as ETDRS chart

21
Q

What are 3 advantages of LogMAR chart over Snellen?

A
  1. All letters are equally legible
  2. Controls crowding phenomenon with 5 letters on each line and appropriate separation
  3. There is logical geometric progression of resolution
22
Q

What do the lines of the logMAR chart score?

A
  • starting with 1.0 line at the top (snellen 6/60), each letter read and scored
  • each correct line (worth 0.1U) or each correct letter (worth 0.02U) is subtracted from 1.0 to give final score
  • 6/6 corresponds with 0.0 score
23
Q

At what distance is the logMAR chart typically used?

A

4m

24
Q

What is the logmar to Snellen conversion?

A
25
Q

What is crowding?

A

phenomenon where neigbouring targets interfere as proximity increases

26
Q

Which patients are particularly susceptible to crowding and what can be done to help this?

A

Amblyopic patients; single optotype tests e.g. Sheridan Gardiner rather than multiple test (e.g. Snellen)

27
Q

How much refractive error can be neutralised by a pinhole?

A

up to 3DS of refractive error

28
Q

What is the structure of a pinhole?

A

stenopaeic aperture, typically 1.2mm in diameter

29
Q

When is the use of a pinhole test useful?

A

to determine whether lower than expected VA is due to optical, rather than patholoical, cause

30
Q

How is near (reading) acuity usually tested?

A

various charts available - paragraphs of text read at pt usual reading distance (30-40cm)

31
Q

How is near visual acuity recorded and what is the normal range?

A

N notation - corresponds to point size of text being read, typical range from N5 - N48 (M notation used in USA - 1M = N48)

32
Q

What does a text size of N5 correspond to in terms of visual acuity?

A

6/12 when read at 30cm

33
Q

What are 2 types of near acuity units in the USA?

A
  1. M notation
  2. J point (Jaeger) - print size for same J point different between charts
34
Q

How should vision be tested if it is <6/60?

A
  • walk pt metre by metre towards chart (or chart to patient).
  • if <0.5/60, test ability to detect hand movements
  • if less than this test light perception (PL) with bright light
  • if PL present try all 4 quadrants and ask pt to point to which quadrant light is perceived as arising from (PL with accurate projection)
35
Q

Why should going straight from <6/60 to counting fingers be avoided?

A

big spectrum between 6/60 to 0.5/60, makes real difference to patients, no adequately represented by CF

36
Q

What do Cardiff cards look like?

A
37
Q

What do Kay picture cards look like?

A
38
Q

What do Keeler cards look like?

A
39
Q

What do Sheridan Gardiner cards look like?

A
40
Q

Waht do Teller cards look like?

A

Investigations (29 decks)

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