Colour sense
Due to excitement by light of different wavelength (cones)
Two main theories
1) trichromatic theory → three kinds of cones exist each different in photopigment and have different maximal sensitive to red(565nm) ,green (535 nm) & blue (440nm) . The sensation of colour vision depends on relative frequency of the impulse thus
A given colour has a certain mixture of three primary colours
2) opponent colour theory → 2 main type of colour ganglion cells via Red-green opponent colour cells and blue-yellow opponent colour cells
Adaptation problems
=divided in to night blindness (nyctalopia) & Day blindness (hamarlopia)
Nyctalopia
→night vision is a function of rods thus problems of these nerve endings cause night blindness . Vitamin A deficiency (needed for Rhodopsin regeneration) , retinitis pigmentosa , congenital high myopia, familial congenital night blindness
- in open angle glaucoma so much so that patient complains of night blindness , i.e. problems with dilated pupil mainly corneal opacities
- also in Ocular media interfering with light rays in dim light
Hamarlopia (day blindness)
- Better night vision than day vision thus some problem with the cones
- → Congenital deficiencies , cataracts and central corneal opacities