Light sensitive receptors present in the retina are called rods and cones. Rods contain a light sensitive pigment rhodospin or visual pigment. Pigment is a conjugated protein. Protein is opsin and the prosthetic group is retinene. These are concerned with dim vision.
Cones are concerned with bright light and colour vision. Three pigments are present in cones. They are porphyropsin, iodopsin and cynopsin which are sensitive to three colours red, green, blue respectively. They are conjugaged proteins – with retinal. Colour perception in colour television is based on mixing of these three basic colours green, blue and red.
When light falls onRhodospin it gets converted to trans retinene and opsin. During its conversion it stimulates the rods. The trans retinene is converted into active form in blue light. This cis retenene again combines with protein opsin to form Rhodospin.
In vivo the trans retinene is reduced to trans retinol, carried by the blood, reaches the liver where tran vit A isconverted to cis Vit A. This reaches the retina where it gets oxidized to cis Vit A retenene. This conjugates with opsin to form Rhodospin.
There are about six set of muscles that help the two eyes work together, to see the same object. If the two eyes work independently, and view different objects simultaneously one can imagine his fate.
Conjunctiva the inner most membrane that lines the eye lids and scelera. Myopia (near sigh) one can see near object clearly. Images of distant objects falls before the retina and hence eye cannot see these objects. Hyperopia in this images of near objects falls far behind he retina. Hence one cannot recognize the near objects. The image of distant objects falls on the retina. Hence one can see far objects. This is called far sight. Protection of eyes is very important. Keep eyes healthy.