Page 1 - Lesson note presbyopia

SAI INTERNATIONAL SCHOOL
PHYSICS
CLASS X
Chapter: LIGHT(Human eye and the colourful world)
MODULE-36

LESSON NOTES: presbyopia,astigmatism,cataract

Presbyopia
o The power of accommodation of the eye usually decreases with ageing. The
ciliary muscles weaken and thereby the flexibility of the eye lens reduces.
o The near point moves away.

o Spectacles with convex lenses are recommended

Myopia and Hypermetropia
o Sometimes a person may suffer from both near sightedness and far-
sightedness.
o Such people are advised to use bifocal lenses.
o Bifocal lenses consists of concave on the upper portion and convex on the
lower portion.
o Concave supports distinct vision and convex supports near vision
Refractive eye defects can also be corrected using contact lenses or through
specific surgical procedures.

Astigmatism is a common vision condition that causes blurred vision. It occurs
when the cornea (the clear front cover of the eye) is irregularly shaped or sometimes
because of the curvature of the lens inside the eye.

A cataract is a clouding of the lens of the eye which leads to a decrease in
vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms
may include faded colors, blurry or double vision, halos around light, trouble with
bright lights, and trouble seeing at night.

Treatment: Glasses, cataract surgery

Causes: Aging, trauma, radiation exposure, fol...

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