Biology 2015 JAMB Past Questions - Question 28: The eye defect that arises because the cornea is notcurved smoothly is

Correct Answer

A

Explanation

Astigmatism is the inability of the eyes tofocus several objects (e.g. vertical and horizontal lines) at a point producingstretched or distorted images. This is because rays of light from these objectsfall on different parts of the retina. A person suffering from astigmatism haslens or cornea which is unevenly curved. (Some areas are steep while others areflat). Presbyopia or old sight occurs as one advances in age. The cells of thelens harden and lose their elasticity, and therefore can no longer be adjusted to focus on near and distant objects. Also the ciliary muscles that control theisms also weakens. Shortsightedness (myopia) -results from the lens of the eye refracting or bending the parallel rays of light entering the eye to a focus in form of the retina generally because of an abnormally long eyeball i.e. the distance of the lens to the retina is too long.This condition is corrected by wearing diverging oi convex lenses to bring theimage back to the retina. The individual sees near objects clearly but distant objects are blurred. Long-sightedness is the ability to see distant objects clearly but near objects appear blurred because rays of light from near objects faii behind the retina. This occurs because the eyeball is too short that is the distance from the lens to the retina is too short.This defect is not caused by any fault on the lens system (oxford dictionary of biology)