Page 1 - Lesson note defects of vision

SAI INTERNATIONAL SCHOOL
PHYSICS
CLASS X
Chapter: LIGHT(Human eye and the colourful world)
MODULE-35

LESSON NOTES: defects of vision, myopia, hypermetropia

Sometimes the eye of a person cannot focus the image of an object on the retina
properly. In such cases the vision of a person becomes blurred and he cannot see
either the distant objects or nearby objects (or both) clearly and comfortably. The
person is said to have a defect of vision.

Three common refractive defects of the eye:
o Myopia or Near-sightedness
o Hypermetropia or Farsightedness
o Presbyopia

Myopia
o Near-sightedness : A person with Myopia can see nearby objects clearly
o A person with myopia cannot see far away objects clearly.
o The far point for the myopic eye is nearer than infinity
o Occurs due to
o Excessive curvature of the eye lens
o Elongation of eyeball
o The image of a distance object is formed in front of the retina and not on the
retina
o Defected is corrected by using Concave lenses such that the lens will bring the
image back on to the retina.

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