a person may suffer from myopia, cataract ,hypermetropia .presopia defects. define with diagram?
give with daigram
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Answers
Nearsightedness, also called myopia is a common name for impaired vision in which a person sees near objects clearly while distant objects appear blurred. In such a defective eye, the image of a distant object is formed in front of the retina and not at the retina itself. Consequently, a nearsighted person cannot focus clearly on an object farther away than the far point for the defective eye.
Causes: This defect arises because the power of the eye is too great due to the decrease in focal length of the crystalline lens. This may arise due to either
(i) an excessive curvature of the cornea, or
(ii) elongation of the eyeball.
Correction:-
This defect can be corrected by using a concave (diverging) lens. A concave lens of appropriate power or focal length is able to bring the image of the object back on the retina itself.
