state the three common defect of eye and how it can be rectified long type question answer
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Answer:
There are mainly three common refractive defects of vision. These are (i) myopia or near-sightedness (ii) Hypermetropia or far – sightedness (iii) Presbyopia. Myopia is also known as near-sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly.
XEROPHTHALMIA :- It is caused by the prolonged deficiency of vitamin A. the lens and cornea became opaque and dry.
Night Blindness :- the retinal, a part of the visual pigment is derived from vitamin A. The deficiency of Vitamin A results in the low production of retinal. This in turn prevents the resynthesis of rhodopsin. In this condition, objects cannot be seen clearly in dim light and this disease is called night blindness.
Cataract :- It is the condition in which the lens of the eyes become opaque resulting in blindness. This can be rectified by replacing the lens with an artificial one, through surgery.