Eye, the photosensitive organ of the human anatomy has a high degree of intricate pattern and embodies highly complex structures in contrast to the minimal size it accounts for. Even the slightest defect in any of the minute assembled parts can leave one prowling for vision for his or her entire lifetime. Nightblindness, one of the most common defects of the human eye stems due to the deficiency of vitamin A in the body. In such a case, synthesis of rhodopsin pigment is curtailed in the rod cells of retina and the person is incapable to seee in dim llight. Another problem that events due to lack of vitamin A in the diet is xerophthalmia, where keratinisation or hardening pf conjunctivia and cornea takes place and conjunctivia becomes solid. Trachoma, another blemish in the beauty of this organ, is caused by a microbe Chlamydia trachomatis, where a watery liquid oozes out from eyes in excessive measure and eyes turn red due to continual irritation. Strabismus or squint eyes occur due to loosening or contraction of any of six skeletal muscles which give the proper position to the eye ball, in its orbit. Thus the eye ball inclines towards one side of the orbit and an operation is performed to get the eye balll back to its proper state. In old age, mostly, cataract sets in the eyes where the lens become more flat, solid, brown and opaque and reduces its power of accomodation. Such a person has zero visibility and a new lens is administered by operation. Normal vision of light is technically called emmetropia, but not all of us are bestowed with such a gift. In case of hypermetropia or far-sightedness, a person is able to see objects placed at a far distancebut is unable to see things close to him. It arises due to small size or flatness of lens and the image forms behind the retina. Convex lenses are used in spectacles in such a case. In old age, the same defect can occur due to abridgement in flexibiltyof lens and is then termed 'presbyopia'. Bifocal lens is used as a cure. In myopia or short-sightedness a person is incapable of seeing objects placed at a far distance due to enlargement of eyeball or increased convexity of lens. Image forms in front of the retina and concave lens are used for cure. In a special case called astigmatism, curvature of cornea is changed as a result of which light rays do not focus on macula lutea or yellow spot (the point where image forms in the eye) but somewhere else harvesting an incomplete and blurred vision. This defect can be remedied by the usage of cylindrical lens. In glaucoma the retina gets damaged due to the blockage of canal of schlemm resulting in complete blindness. Proper image is not formed in bright light in case of photophobia. Colour blindness is a genetic disorder of X-chromosome which stems dut to recessive genes. Such a person cannot differentiate between red and green colour.

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