Visual acuity

Question 1

What are 5 stages of assessing visual acuity?

Answer 1

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

Question 2

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

Answer 2

1. Snellen
2. Logmar

Question 3

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

Answer 3

1. Test type N chart
2. Logmar

Question 4

What are 3 distance visual acuity tests for illiterate adults?

Answer 4

1. Keeler Logmar
2. Sheridan Gardiner
3. Kay picture test

Question 5

What is 1 near visual acuity tests for illiterate adults?

Answer 5

1. Reduced Sheridan Gardiner

Question 6

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

Answer 6

1. LogMAR
2. Keeler LogMAR
3. Kay picture test

Question 7

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

Answer 7

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

Question 8

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

Answer 8

Reduced Kay picture test

Question 9

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

Answer 9

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

Question 10

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

Answer 10

1. Keeler
2. Teller
3. Cardiff cards

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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

Question 14

What is normal Snellen acuity in the young eye?

Answer 14

1min of arc or 6/6

Question 15

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

Answer 15

5s of arc

Question 16

What change in Snellen acuity should be regarded as significant?

Answer 16

change of 2 lines

Question 17

What is decimal acuity from a Snellen chart?

Answer 17

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

Question 18

What do LogMAR charts record?

Answer 18

the logaritm of the minimum angle of resolution

Question 19

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

Answer 19

Bailey-Lovie LogMAR chart - 5

Question 20

Which LogMAR chart is in common usage?

Answer 20

Ferris modification, known as ETDRS chart

Question 21

What are 3 advantages of LogMAR chart over Snellen?

Answer 21

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

Question 22

What do the lines of the logMAR chart score?

Answer 22

• 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

Question 23

At what distance is the logMAR chart typically used?

Answer 23

4m

Question 24

What is the logmar to Snellen conversion?

Answer 24

Question 25

What is crowding?

Answer 25

phenomenon where neigbouring targets interfere as proximity increases

Question 26

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

Answer 26

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

Question 27

How much refractive error can be neutralised by a pinhole?

Answer 27

up to 3DS of refractive error

Question 28

What is the structure of a pinhole?

Answer 28

stenopaeic aperture, typically 1.2mm in diameter

Question 29

When is the use of a pinhole test useful?

Answer 29

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

Question 30

How is near (reading) acuity usually tested?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

6/12 when read at 30cm

Question 33

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

Answer 33

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

Question 34

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

Answer 34

* 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)

Question 35

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

Answer 35

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

Question 36

What do Cardiff cards look like?

Answer 36

Question 37

What do Kay picture cards look like?

Answer 37

Question 38

What do Keeler cards look like?

Answer 38

Question 39

What do Sheridan Gardiner cards look like?

Answer 39

Question 40

Waht do Teller cards look like?

Answer 40