Defects of Human Eye & its correction.

1. Defects of human Eye &
their correction
- Mihir Bhayani
B.E. Mechanical,
Savitribai Phule University

2. R.S.Academy,Pune
Terms Related to Human Eye
Accomodation: It is the ability of eye lens to focus both near & distant objects
Clearly.
 Power of Accomodation: it is the max. variation in power of eye lens.
 Far Point of Eye: It is the farthest point upto which the human eye can clearly see
different objects.
 Near Point of Eye: The minimum distance upto which an object can be seen
distinctly is called near point.
 Persistence of Vision: It is the minimum time for which any object should be seen
to capture its image by the human eye.

3. R.S.Academy,Pune
Myopia
NEAR-SIGHTEDNESS or SHORT-SIGHTEDNESS
 The person suffering from myopia can see near objects clearly but distant
objects seem to be blurry as the image is formed in front of the retina.
 CAUSES:
 Increase in curvature of lens
 Increase in length of eyeball.
 CORRECTION:
 It can be corrected by using a suitable concave lens of appropriate focal
length which can focus the image backwards on the retina.

4. R.S.Academy,Pune
NORMAL EYE
Image is formed on retina
Retina
Retina
MYOPIC EYE
Image is formed in front of retina
CORRECTED EYE
Concave lens focusses the image on
the retina.
Thus image is formed on retina.

5. R.S.Academy,Pune
Hypermetropia
FAR-SIGHTEDNESS or LONG-SIGHTEDNESS
 The person suffering from hypermetropia cannot see near objects clearly but
distant objects are visible clearly as the image is formed behind the retina.
 CAUSES:
 Decrease in curvature of lens
 Decrease in length of eyeball.
 CORRECTION:
 It can be corrected by using a suitable convex lens of appropriate focal
length which can focus the image on the retina.

6. R.S.Academy,Pune
NORMAL EYE
Image is formed on retina
Retina
Retina
HYPERMETROPIC EYE
Image is formed behind the retina
CORRECTED EYE
Convex lens focusses the image on
the retina.
Thus image is formed on retina.

7. R.S.Academy,Pune
Presbyopia
Presbyopia is a natural part of the aging process.
 It is a type of refractive error along with nearsightedness, farsightedness, and
astigmatism.
 CAUSES:
 Hardening of the eyes
 Weakening of ciliary muscles.
 Decreased flexibility of the eyes.
 CORRECTION:
 It can be corrected by using a bifocal lenses consisting of both
convex and concave lenses.

8. R.S.Academy,Pune
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