Eye is the organ of sight which detect changes and give signals to the central neural system. It is located in eye sockets of the skull, and adapted for binocular vision, these are protected by the eyebrows, eyelids and lachrymal glands. The wall of the human eye is composed of three layers. Sclera, choroid and retina. The anterior portion of the sclera is the cornea. choroid forms the ciliary body which forms the iris, The eyeball contains a transparent crystalline lens held in place by the ligaments of the ciliary body. In front of the lens, the iris, which regulate the diameter of the pupil. The inner layer is the retina which contains three layers of cells consisting of ganglion cells, bipolar cells and the photoreceptor cells.– Photoreceptor cells are of two types rods and cones. Rhodopsin of rods, is sensitive to dim light, these do not play any role in colour vision. Iodopsin of cones, is sensitive to bright daylight. Cones are of three types and contain different photo pigments and respond to red, green and blue light radiations. The optical part of the retina contains two spots known as the blind spot and the fovea.
The aqueous chamber lies between the cornea and lens called, an aqueous humor that provides nutrition to the lens and cornea. The vitreous chamber lies between the lens and retina. It is filled with vitreous humor that gives shape to the eye, supports the retina and lens, refracts light rays and maintains intra-ocular pressure. The human eye works like a camera. The cornea, aqueous humor, lens and vitreous humor, all act as small lenses and refract light rays to focus on the retina. The light rays in the visible wavelength focus on the retina to generate impulses in the rods and cones. The photo pigments of the photoreceptors opsin and retinal. Light dissociates retinal from opsin, which results in changing the structure of opsin. The structural change in opsin changes membrane permeability, which in turn, results in potential differences in the photoreceptor cells. This results in the generation of action potential which is transmitted to the visual area of the cerebrum by the optic nerve. These nerve impulses are analysed in the visual area and help to recognise the image formed.