Colour Vision

Question 1

What is Purkinje shift?

Answer 1

In dark adapted state, wavelengths of 500nm appear the brightest and in photopic conditions wavelegths of 555nm (yellow/green) appear brightest.

Short wavelengths becoming brighter compared with long wavelegths as luminance is reduced is known as the Purkinje shift

Question 2

How is colour blindness tested?

Answer 2

Hue discrimination technique - frasworth munsel 100 hue test

Question 3

What are the types of cones?

Answer 3

Long wavelength senstive RED cones with peak sensitivity 570-590

Medium wavelength senstivity - green cones - 535-550nm

Short wavelegth sensitve Blue cones - 440-450nm

Blue are the most infrequent at the fovea

Three cone opsins differ in their transmembrane regions of the proteins

Less sensitve than rhodopsin but repsond faster

Question 4

What is rod monochomatism?

Answer 4

True achromatic vision
Low VA
Photophobia
Nystagmus

Question 5

What is cone monochromatism

Answer 5

Normal VA
Cannot disriminate coloured lights of equal luminosity

Question 6

What is dichromatism?

Answer 6

Matches all colours with mixures of two primaries

Protanopes - missing red
Deuteranopes - missing green
Tritanopes - missing blue

Question 7

What is anomalous trichromatism?

Answer 7

Use different proportions of the 3 primary colours to match colour

Question 8

What are the types of colour opponent ganglion cells?

Answer 8

REd green - use signals from red green cones to detect red green contrast

Blue uellow - obtain yellow signal from summed output of red and green cones which is contrasted with output of blue cones

Question 9

How is colour information processed?

Answer 9

Follows parvocellular pathway to V1 and V2 of visual cortex and to V4 which is main colour area of cortex - mediates colour constancy - things same colour perceived in different light

Question 10

What defects to optic nerve diseases produce

Answer 10

Red/green except glaucoma - blue yellow

Question 11

What colour defects to retinal diseases prodcue?

Answer 11

Blue uellow

Question 12

Where are the genes for each colour located

Answer 12

red and green on X chromosome - common protanomaly deuteranomaly - Xlinked recessive
Blue on chromosome 7 - very rare autosomal dominant

Question 13

What is the most common colour vision defect

Answer 13

M cone mutation
Deuteranomaly - weakening ability to differentiate red and green hues

X linked recessive