There are two main types of vision defects: myopia and hypermetropia. Myopia, or nearsightedness, causes a person to see nearby objects clearly but not distant objects, because the image is focused in front of the retina. It is caused by elongation of the eyeball or a decrease in the lens's focal length. Hypermetropia, or farsightedness, has the opposite effect - distant objects are seen clearly but not nearby ones, as the image is focused behind the retina, due to shortening of the eyeball or an increase in the lens's focal length. Both conditions can be corrected using convex or concave lenses, respectively, to properly focus the image on the retina

1. DEFECTS OF VISION
Ushakumari.V
Christ nagar senior secondary school
Thiruvallom

2. EYES- OUR WINDOWS TO THE WORLD!

3. Spectacles
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WHY SO
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4. DEFECTS OF VISION
 When normal functioning
of the eye is affected , it
results in defects of
vision
 Mainly 2 types
 Myopia (short
sightedness)
 Hypermetropia
(long sightedness)

5. NORMAL EYE
In a normal eye , light passes through the
cornea , and the image is focused by the lens on
the retina

6. WHAT IS THE DIFFICULY HERE????????

7. MYOPIA- NEARSIGHTEDNESS
 A person can see nearby objects clearly and
distinctly but cannot see far away objects clearly.
 In myopic eye ,the image is formed in front of the
retina.
 Caused by two reasons:
 Elongation of the eyeball  so images are focused in
front of the retina
 Decrease in the focal length of eye lens
 Correction: by using a concave lens of appropriate
power.

8. MYOPIC EYE

9. MYOPIC EYE-IMAGE FORMATION

10. MYOPIC EYE – RAY DIAGRAM &
CORRECTION USING CONCAVE LENS

11. CAN YOU SEE PROPERLY ?????

12. HYPERMETROPIA – FAR SIGHTEDNESS
 The person can see distant objects clearly and distinctly
but cannot see nearby objects clearly
 The image is focused behind the retina
 Main causes are :
 Shortening of the eyeball  So the images are focused
behind the retina
 Increase in focal length of the eye lens
 Correction: by using a convex lens of appropriate
power

13. HYPERMETROPIC EYE

14. HYPERMETROPIC EYE – IMAGE
FORMATION

15. HYPERMETROPIC EYE – RAY DIAGRAM
AND CORRECTION USING CONVEX LENS

16. SUMMING
UP ….