Construction of Human Eye

1
Human Eye

• Construction of Human Eye
• iris, pupil, cornea, aqueous humour, lens,
  ciliary muscle, vitreous humour, retina
• Focusing
• seeing near object ( near point )
• seeing distant object ( far point )
• Eye defects
• Short-sight
• Long-sight

2
Construction of human eye
Retina
iris
Cornea
pupil
Blind spot

• eye lens

Ciliary muscles
Vitreous humour
3
Formation of image

• Light entering the eye is refracted successively
  at the cornea, the aqueous humour, the lens and
  the vitreous humour.
• The image is formed on the retina and the retina
  sends signal along the optical nerve to the
  brain, causing the sensation of sight.
• The image formed on the retina is inverted but is
  interpreted as erect.

4
Focusing near object

• Light from near object

5
Focusing far away object

• Light from far away object

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

9
Causes of short sight

• The eyeball is a bit too long.
• The lens lacks the ability to accommodate for a
  distant object.

10
Correction of short sight

• Light from distant object

11
Long sight

• Light from near object

12
Causes of long sight

• The eyeball is a bit too short.
• The lens lacks the ability to accommodate for a
  near object.

13
Correction of long sight

• Light from near object

14
Summary
15
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 chaning the
focal length of the eye 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.