What is cone cells:
Cones secreted by cone cells. Produce "Iodopsin" which is visual violet and made up of photopsin+11 cis retinal. It is sensitive to colour. Cones are active in bright light which is called photopic vision. In fovea centralis only cone cells are present. Cones are more in number in central region of retina Cones are more in diurnal animals. In fowls only cones are present and rods are absent. 6 million cones in human.
Light passes through many refractive surface before it is focussed on the retina forming an inverted and true image.The main site of refraction are cornea-aqueous humor-iris-lens(position can be altered by ciliarybody:accommodation)-posterior chamber (=vitreous humor )-retina(in fovea).The refractive index of the eye varies from 59 diopter(when the lens is at rest) to about 71 diopter(when lens is bulging in maximum accommodation).The accommodation reflex occurs when the eye changes its focus from a far away object to nearer one.The change in strength of the lens provides the physiological basis of accommodation.Radial and circular muscle fibres of ciliary muscles play an important role in this as they contract reflexively (parasympathetic control) and increase lens strength.The pupil of constricts. This faciliates increase in sharpness of image.Ageing causes loss of accommodation.
Type of vision
a. Binocular vision
Man has binocular vision in which both the eyes are focussed on the same object but from slightly different angles.The visual fields of both eye overlap and the foveae of both are focused on the same object.This provides depth to the images. ie.,gives stereoscopic or 3D effect and enables man to judge distances correctly.
b. Vision in other animals
Primates and predatory animals ,such as owl and cat,have binocular vision. In some animals ,such as rabbit,birds,each eye is focussed on a separate object. This is termed monocular vision.
It is the ability of some animals to detect colours in an object.Humans,apes ,monkeys and most fishes,amphibians,reptiles and birds have strong colour vision. The insects and cryfish also have colour vision.In vertebrates ,colour vision results from the activity of cone cells.Most domestic and nocturnal mammals and sharks lack colour vision.They probably see objects in shades of grey(monochrome vision).
Nocturnal and Diurnal vision
Man has both day vision and night vision as he has both rods and cones in cosiderable numbers in the retina.Most birds have only day vision as their retina contains mainly cones. Owls has much better night vision than day vision for they possess a large number of rods and few cones in their retina.
Range of vision
The visible range of spectrum varies in animals .Bees,ants,spider and goldfish can see ultraviolet light,which is invisible to man.
Correspondence between Camera and Eye
|2.||Black inner paint||Choroid|
|7.||Light-sensitive plate or film||Retina|
|8||Image small and inverted||Image small and inverted|