Contrast and colour

Question 1

What degree of contrast is tested on visual acuity charts e.g. Snellen and how does this differ in real life?

Answer 1

they test high contrast (black letters on white background), most tasks require resolution of low/medium contrast

Question 2

What are 3 examples of contrast sensitivity charts?

Answer 2

1. Vistech chart
2. Pelli-Robson chart
3. Cambridge chart

Question 3

What is the Vistech chart?

Answer 3

employs rows of broken circles which decrease in contrast across the row and dmiminish in size from row to row. identification of target orientation is plotted on a template to give a graph of contrast vs spatial frequency

Question 4

At what 2 distances can the Vistech chart be used?

Answer 4

1. 45cm
2. 3m

Question 5

What is the Pelli-Robson chart?

Answer 5

triplets of capital letters, usually read at 1m, until 2 or 3 mistakes in one triplet

Question 6

What is the Cambridge chart?

Answer 6

square wave gratings, usually read at 6m, forced choice at to which of 2 luminance-matched pages the grating is on

Question 7

At what distance is the Pelli-Robson chart performed?

Answer 7

1m

Question 8

What what distance is the Cambridge chart performed?

Answer 8

6m

Question 9

In addition to Vistech, Cambridge and Pelli-Robson charts how do other contrast assessment charts work?

Answer 9

vary the visual acuity of the task at a specific contrast such as the high (~90%) and low (~10%) logmar chart

Question 10

How do newer tablet-based charts for contrast vision work?

Answer 10

patients can outline with their fingers where contrast gratings are visible to them, allowing information from multiple spatial frequencies to be quickly assessed

Question 11

What are 6 tests of colour vision?

Answer 11

1. Testing red desaturation
2. Ishihara pseudo-isochromatic plates
3. Hardy-Rand-Rittler plates
4. Holmes Wright lantern
5. Farnsworth-D15 test
6. Farnsworth-Munsell 100-Hue test

Question 12

How can red desaturation be tested?

Answer 12

comapre perception of redness (e.g. of a red pin) between eyes, occluding one at a time -for central or peripheral vision

Question 13

What type of disease can cause central vision red desaturation?

Answer 13

optic neuropathy

Question 14

What type of disease can cause peripheral field red desaturation?

Answer 14

bitemporally reduced in chiasmal lesion

Question 15

How can red desaturation be graded?

Answer 15

approximate score can be assigned by the
patient to the ‘washed-out’ image in relation to the normal image, e.g. 5/10.

Question 16

At what distance and under what conditions are Ishihara pseudo-isochromatic plates used?

Answer 16

2/3m under good illumination in patients with VA >6/18

Question 17

Who can see the first Ishihara test plate?

Answer 17

even achromatis with sufficient acuity can see it

Question 18

What type of colour blindness do Ishihara plates test?

Answer 18

red-green confusion

Question 19

What can some Ishihara plates distinguish between?

Answer 19

some differentiate whethere defect of the protan (red) or deutan (green) system - doesn’t test tritan system

Question 20

What type of mistakes are made in congenital red-green colour blindness bs acquired colour blindness with Ishihara plates?

Answer 20

congenital=predictable, acquired=do not follow specific pattern

Question 21

What is the advantage of Hardy-Rand-Rittler plates over Ishihara plates?

Answer 21

test tritan as well as protan and deutan discrimination

Question 22

What is the Holmes Wright lantern?

Answer 22

test of binary choice of two or three coloured spots of light viewed at 6m - colours are red, green and white

Question 23

What is the function of the Holmes Wright lantern?

Answer 23

is a more practical assessment that aims to predict red-green
discrimination in a work situation, e.g. distinguishing red and green lights
on a runway

Question 24

What is the Holmes Wright lantern used in conjunction with for testing colour vision in military personnel?

Answer 24

Ishihara plates

Question 25

What is the Farnsworth-D15 test?

Answer 25

screening test for vision - colour tile ordering test of confusion

Question 26

How much information does the Farnsworth-D15 test given on protan, deutan and tritan systems?

Answer 26

limited information

Question 27

What does the Farnsworth-Munsell 100-Hue test involve?

Answer 27

time-consuming colour tile ordering test of discrimination where patient attempts to order 85 coloured caps by hue

Question 28

How can the Farnsworth-Munsell 100 hue test provide information on protan, deutan and tritan systems?

Answer 28

when plotted onto a dedicated chart

Question 29

What is often used as the final arbitrator for colour vision-requiring professions?

Answer 29

Farnsworth-Munsell 100-Hue test