DEFECTS OF VISION

Short-sightedness and long-

sightedness

Image is focused exactly on the retina

Normal sight

Short- sightedness

Symptoms:

•Sees near objects clearly•Distant objects are blurred

Short-sightednessCauses:

•The lens is too thick.•The eye ball is too long

Light from a distant object is focused in front of the retina.Image that falls on the retina is blurred

How to correct short-sightedness?

Wear glasses with concave lenses

CORRECTION OF SHORT-SIGHTEDNESS

Symptoms:sees distant objects clearlynear objects are blurred

Long-sightedness

Long-sightedness

Causes:•The lens is too thin•The eyeball is too short

Long-sightedness

Light is focused behind the retina

How to correct long-sightedness

Wear glasses with convex lens

Comparison between short-sightedness and long-sightedness

Astigmatism

Either caused by irregular lens or cornea or both

Astigmatism

A person suffers from astigmatism sees some parts of an object more clearly than other parts

Correction of astigmatismBy wearing glasses with cylindrical lenses, wearing special contact lenses or surgery

Devices to overcome limitation of sight