Contrast Sensitivity

Question 1

81 year old patient
VA: R: 0.020 (6/6-1) L: 0.040 (6/6-2) etdrs chart
NVA: R: 6/6 L: 6/6 reduced Snellen chart
BEO: N5 read fluently Moorfields bar reading book

Tells you she struggles with her vision especially at night and can’t see food on her plate or read well.

What’s this patient’s diagnosis?

Answer 1

Reduced Contrast Sensitivity

Question 2

What’s the definition of contrast?

Answer 2

The difference in luminance of adjacent field or objects

Question 3

What is contrast sensitivity?

Answer 3

The ability to detect objects at low contrast

Contrast sensitivity defines the threshold between the visible and invisible

Question 4

What is visual acuity?

Answer 4

The ability to resolve a pattern into spatially separate elements

Question 5

Why is contrast sensitivity important?

Answer 5

• Driving (especially at night)
• Reading
• Navigation

Question 6

How do we measure contrast?

Answer 6

Difference in Luminance / Average Luminance

Question 7

What’s the contrast threshold?

Answer 7

The least amount of contrast necessary to allow detection

Question 8

How do we measure contrast sensitivity?

Answer 8

1 / Contrast Threshold

A measure of the ability to detect patterns and objects at varying contrast levels

Question 9

What frequency do we use to measure contrast sensitivity?

Answer 9

Can be measured using gratings of varying spatial frequency

Spatial frequency - cycles per degree at nodal point of eye e.g. 5 cpd is a higher spatial frequency than 2 cpd

Question 10

What does it mean that spatial frequencies are in units of cycles per degree of visual angle?

Answer 10

It implies that the visibility of details at a particular frequency is a function of viewing distance

Question 11

When measuring contrast sensitivity, we use a range of what 2 levels?

Answer 11

• Spatial Frequencies
• Contrast Threshold

Question 12

What is contrast sensitivity function (CSF)?

Answer 12

Contrast sensitivity function(CSF) is the curve that defines the lowest contrast level that you can detect for each spatial frequency tested.

A graph is plotted setting out contrast threshold for each spatial frequency.

Question 13

What is the critical spatial frequency?

Answer 13

Grating can’t be detected even at maximum contrast (Critical spatial frequency)

Question 14

Can a patient have normal VA but reduced contrast sensitivity?

Answer 14

Yes

Question 15

What information does contrast sensitivity give us?

Answer 15

Measuring contrast sensitivity provides additional information on the quality of vision - things like cataracts, glaucoma, age-related macular degeneration and retinitis pigmentosa can reduce CS

Question 16

What did Xiong et al (2020) find about contrast sensitivity and ocular disease?

Answer 16

• Cataract and Glaucoma, poor VA and reasonable CS.
• AMD and RP (Retinitis Pigmentosa) poor VA correlated with poor CS.

Question 17

Can contrast sensitivity help in detecting and monitoring ocular diseases?

Answer 17

Yes

Question 18

What might contrast sensitivity be useful in monitoring?

Answer 18

• Optic neuritis (Retrobulbar neuritis)
• Optic nerve compression (e.g in graves orbitopathy = thyroid eye disease)
• Optic pathway glioma
• Cataract
• Glaucoma
• Macular disease
• Retinitis pigmentosa
• Amblyopia

Question 19

What might we see in reference to the contrast sensitivity in anisometropic & stimulus deprivation amblyopes?

Answer 19

Contrast sensitivity reduced at all spatial frequencies tested.

Question 20

What might we see in reference to the contrast sensitivity in strabismic amblyopes?

Answer 20

Contrast sensitivity reduced for high spatial frequencies only.

Question 21

In amblyopes, can contrast sensitivity improve?

Answer 21

Contrast sensitivity may improve during amblyopia treatment, however not to the same level as normal subjects even without improvement to VA.

Question 22

What can contrast sensitivity in low vision predict?

Answer 22

• Predicts persons mobility
• Indicates which eye will give the better reading performance
• Explains why some patients cannot attain sufficient reading speeds despite reasonable visual acuity and provision of appropriate magnification

Question 23

What charts are there of clinical contrast sensitivity?

Answer 23

• Pelli-Robson contrast sensitivity test
• Bailey-Lovie LogMAR low contrast chart
• The Mars Letter Contrast Sensitivity Test
• Test chart 2000 (Thompson)
• American optical contrast sensitivity test
• Vistech vision contrast test system
• CSV1000E Contrast Chart

Question 24

How does the Pelli-Robson chart work?

Answer 24

• Identical size letters in groups of 3 (triplet) approx 1.5cpd
• Each group of 3 letters has same contrast
• Contrast decreases from 100% to 0.5%
• Tested at 1m

Question 25

What is the average score on the Pelli-Robson chart for 22yo's and 70yo's?

Answer 25

Elliot et al (1990) 1.80 log units - mean 22yrs 1.65 log units - mean 70yrs

Question 26

What is the preferred contrast sensitivity chart? (57% UK Orthoptists recommend)

Answer 26

Pelli-Robson as it has high repeatability of 92-94%

Question 27

What is the Bailey-Lovie Low Contrast Test? How does it look?

Answer 27

It is a contrast sensitivity chart with 10% contrast that can be directly compared with the normal high-contrast chart. Usually there are around 7-11 letters difference.

Question 28

What is the Mars Letter Contrast Sensitivity Test?

Answer 28

It's a hand-held contrast sensitivity chart that's viewed from 41 - 59cm with a contrast range from 0.04 to 1.92 logMAR. Each successive letter decreases in contrast by 0.04 logMAR 3 versions with a difference sequence of Sloan letters Need to wear +2.00DS lens to correct working distance in Presbyopic patients

Question 29

What is the Test Chart 2000?

Answer 29

A computerised Contrast Sensitivity Test that presents optotypes on a computer monitor viewed at 1m. Same as Pelli-Robson but only one triplet presented per line

Question 30

Given the Test Chart 2000 is based off of Pelli-Robson, do they have good agreement?

Answer 30

Mars Chart and Pelli-Robson chart show reasonable agreement Test Chart 2000 and Pelli-Robson chart do not show good agreement. (This could be due to poor performance of liquid crystal display screens at low contrast levels.)

Question 31

What's the American Optical Contrast Sensitivity Test?

Answer 31

There is a demonstration plate and 6 other plates ranging from 0.2 - 6.4cpd and is presented at 57cm. Average score is <62, Borderline = 78 & Abnormal is >82

Question 32

How is the American Optical Contrast Sensitivity Test conducted?

Answer 32

- Patient instructed to look at border with box and say when ‘stripes’ first seen as plate withdrawn - Plate moved slowly (about 20 secs to reveal) - Can confirm seen by asking patient to indicate dark ‘stripe’ – can be used in children - Score for plate noted

Question 33

How is the Vistech Contrast Test conducted?

Answer 33

- Patient indicates if grating tilted to left or right - Test performed at 3m - Near chart available

Question 34

What is the CSV1000E Contrast Chart?

Answer 34

A contrast sensitivity chart 4 rows of sine-wave gratings Spatial frequencies of: 3, 6, 12, and 18 cyc/deg Test at 2.5 meters

Question 35

What contrast sensitivity charts do you use in young children?

Answer 35

- Peek-a-boo Patti / Hiding Heidi - Lea symbols - Cambridge low contrast grating

Question 36

What is the Hiding Heidi test?

Answer 36

A test of contrast sensitivity in young children Face revealed from covered position and child observed to see if follows / responds to face ‘Know’ patient’s reactions to face / toys prior to testing Contrast levels: 1.25%, 2.5%, 5%, 10%, 25% & 100% Mixed spatial frequencies: 9, 3, 1.5 & 0.75 cpd Preferential looking Tested at 1m

Question 37

What is the Peek-a-boo Patti test?

Answer 37

A test of contrast sensitivity in young children For testing: typically developing toddlers/young children and older children / adults with learning difficulties. Pictures of the same size that decrease in contrast between light and dark bands. The contrast sensitivity is determined by the faintest bands for which the target is visible 12 contrast levels - 3 cards at each level (36 cards total) Preferential looking technique Contrast levels 46% to 1% 50 cm, 1.9 cycles per degree (or 6/90, 20/300) 1 m , 3.8 cycles per degree (or 6/45, 20/150) 25 cm, 1.0 cycle per degree (or 6/180, 20/600)

Question 38

What is the Cambridge Low Contrast Gratings?

Answer 38

A contrast sensitivity test in young children

Question 39

How is the Cambridge Low Contrast Gratings performed?

Answer 39

Grating effect created by dots on one page only, intensity of dots governs contrast (5% to 0.14%) Tested at 6m, illumination 100cd/m2 (well lit room) Two pages displayed, one filled with dots – other dots only in stripes (4 cycles/degree), child asked to indicate page with stripe Proceed until not seen, then go back 4 plates – repeat 3 more times, then add scores for 4 series and read CS from table (10 to 560) Normative data published for different age groups. However, caution due to lack of repeatability over time (Jones et al, 1994)