1. Human Eye Structure of Human Eye: Focusing Eye defects
Eye Muscles, Optic nerve, sclerotic coat
Cornea, iris, pupil,, lens, retina, blind spot
aqueous humour, vitreous humour, ciliary muscle
Focusing
seeing near object ( near point )
seeing distant object ( far point )
Eye defects
Short sight
Long sight

2. Structure of human eye Retina iris Cornea pupil Blind spot lens
Focusing muscles
Vitreous humour

3. Formation of image
Light entering the eye is focused successively by the len onto the retina.
The image formed on the retina is inverted but is interpreted as erect.
The retina contains many light sensitive cells sends signal along the optic nerve to the brain, causing the sensation of sight.

4. Focusing near object
Light from near object
Clear image

5. Focusing far away object
Light from far away object
Clear image

6. Accommodation

7. Near Point and Far Point
The average normal eye can focus objects easily from about 25 cm, i.e., the near point, to infinity, i.e. the far point.
This range of distance of clear vision varies from one person to another and decreases with age.

8. Short sight Light from distant object blurred image in front of
The image is focused ____________ the retina
in front of

9. Causes of short sight The eyeball is too long.
The lens lacks the ability to accommodate for a distant object.

10. Correction of short sight
Light from distant object
Concave lens
( Diverging lens )

11. Long sight Light from near object blurred image behind
The image is focused ________ the retina
behind

12. Causes of long sight The eyeball is too short.
The lens lacks the ability to accommodate for a near object.

13. Correction of long sight
Light from near object
Convex lens
( Converging lens )

14. Summary

15. 1. Which of the following statements about the lens is/are correct ?
Class Practice
1. Which of the following statements about the lens is/are correct ?
(1) The image formed on the retina is real.
(2) The pupil is smaller in bright light than in dim light.
(3) When the object distance changes, the eye focuses an object by changing the focal length of the lens.

16. Class Practice
2. The near point of a long-sighted eye is 50 cm from the eye. A lens is used for correction.
(a) What type of lens should be used ?
(b) Find the focal length of the lens.