Contrast Sensitivity

Question 1

What does visual acuity test in regard to contrast and target size?

Answer 1

High Contrast and small targets

Question 2

What is Weber Function?

Answer 2

Contrast= (Lt-Lb)/ Lb

Lt= Luminance of target
Lb= Luminance of background

Question 3

What is Michelson Contrast?

Answer 3

Contrast= (Lmax-Lmin)/ (Lmax+ Lmin)

Question 4

Between Weber and Michelson contrast- which is more often used?

Answer 4

Michelson Contrast

Question 5

What is contrast sensitivity?

Answer 5

The reciprocal of contrast threshold. Which can be determined by going from seeing -> non seeing or vice versa

Question 6

Contrast sensitivity curve

Answer 6

If there is low spatial frequency meaning the threshold is low since it is easily distinguishable (high contrast) then the sensitivity is medium

If there is high spatial frequency meaning the contrast threshold is high then the sensitivity is low

The highest sensitivity (being able to differentiate the stripes) is from medium spatial frequency (3.5cpd)

Question 7

What does one cycle of spatial frequency contain?

Answer 7

One light bar (peak) and one dark bar (trough)

Question 8

What is the smallest grating a patient can resolve and what is its SF?

Answer 8

SF= 20cpd
Snellen VA= 20/30
logMAR= 1.5

Question 9

What is type 2 CS loss?

Answer 9

Pt has difficulty with all SFs and will have reduced VA

Question 10

What is type 1 CS loss?

Answer 10

Pt has difficulty with high SF and will have reduced VA
They have normal response to lower SFs

Question 11

What is type 3 CS loss?

Answer 11

Pt has difficulty with low SFs and has normal responses to higher SFs they will have NORMAL VA

Question 12

What is type 3 CS loss found in?

Answer 12

Optic Neuritis
MS
Parkinsons
Diabetes
Primary Open angle glaucoma
Papilledema
Alzheimer’s

Question 13

How are contrast threshold and contrast sensitivity correlated?

Answer 13

Each 2x increase in threshold produces a 0.3 decline in log contrast sensitivity

Question 14

What is the pelli robson chart good for? What is it performed at?

Answer 14

It is good for testing low SF loss and is performed at 1m with a series of triplets of letters size: 20/666

Question 15

What is the relationship between contrast threshold and contrast sensitivity for each line of the pelli-robson chart?

Answer 15

Each triplet set of letters has 0.15 log units higher contrast sensitivity then the preceding test

• Contrast sensitivity increases because contrast decreases

Question 16

What is a MARS test?

Answer 16

It is a pelli robson test but smaller and performed at 0.5m

Question 17

What is Spot check?

Answer 17

Worksheet with 24 rows of spots that decrease in Weber contrast from top to bottom

Performed at 40cm with each spot subtending 1.3 degrees and a decrease in 0.01logCS from left to right

Question 18

What is a Melbourne Edge Test?

Answer 18

It is 20 bisected circular patches of decrease contrast

The test is independent of VA so it is good for low vision pt

Question 19

What is a vistech chart?

Answer 19

Contrast decreases from left to right and spatial frequency increases from top to bottom

The gratings go from 1.5-18cpd
The test is performed at 3m

Question 20

What are the benefits of contrast sensitivity?

Answer 20

1. Can detect visual loss that would be missed by testing VA alone
2. Gives a much better assessment of visual performance in the real world
3. Highest predictor of falls in elderly
4. Best predictor of driving recognition performance