What is eye ?
Human eye have binocular vision.The eye can discriminate colour,appraise length,width and depth visually and form true inverted image.
Structure of eye
The eye are two in number and lodged in orbits(bony socket) of skull. The eye is a hollow ,spherical organ,about 2.5cm in diameter and about 6 to 8 gram in weight.It has two parts-
Eye has four protective devices.
The outwardly directed hair of the eyebrows carry the sweat and rain drops trickling down the forehead to the sides to prevent their falling into the eyes
In man two eyelids are present,upper is movable.They are regularly closed at short intervals to clean the cornea.This is called blinking. In frog out of two upper eyelid is immovable and lower eyelid is movable. Nictitating membrane is present in frog which protect eye in water . Movement of nictitating membrane tekes place by retractor bulbi.It becomes folded by levator bulbi.
A nonfunctional vestigeal nictitating membrane,called plica-semilunaris, occurs in human eyes. It remains permanently retracted at the inner angle of each eye.