Defects in Human Eyes

Defects in Human Eyes

Myopia | Hypermetropia | Astigmatism

How to correct the defects?

Myopia:

Nearsightedness, also called myopia is common name for impaired vision in which a person sees near objects clearly while distant objects appear blurred.  

Cause:

(1) In such a defective eye, the image of a distant object is formed in front of the retina and not at the retina itself.

(2) Another reason could be due to longer eye ball.

Consequently, a nearsighted person cannot focus clearly on an object farther away than the far point for the defective eye

Eye care professionals most commonly correct myopia through the use of concave lenses. A concave lens diverges the rays of light entering the eye in such a way that the rays focus on retina.

Hypermetropia:

Farsightedness, also called hypermetropia, common name for a defect in vision in which a person sees near objects with blurred vision, while distant objects appear in sharp focus. 

Cause:

(i) In this case, the image is formed behind the retina.

(ii) Another reason could be due to shorter eye ball.

This defect can be corrected by using a convex (converging) lens of appropriate focal length. The convex lens converges the rays of light on the retina, forming a clear image.

Astigmatism:

Astigmatism, a defect in the outer curvature on the surface of the eye that causes distorted vision.In astigmatism, a person cannot simultaneously focus on both horizontal and vertical lines. This defect can be corrected by using eyeglasses with cylindrical lenses oriented to compensate for the irregularities in the cornea.