Class X SCI CH 2 Session 5

2. CHAPTER 2
WINDOWS OF KNOWLEDGE
CHAPTER 2
WINDOWS OF KNOWLEDGE

3. LET’S REVISE
The chemistry of vision
 Binocular vision

4. EYE – DEFECTS AND DISEASES
 Myopia ( short sight )
It is a common vision condition in
which you can see objects near to you
clearly, but objects farther away are
blurry.
It occurs when the shape of your eye
causes light rays to bend incorrectly,
focusing images in front of your retina
instead of on your retina.

6. EYE – DEFECTS AND DISEASES
 Hypermetropia ( long sight )
Hypermetropia is a common eye
condition where nearby objects appear
blurred, but your vision is clearer when
looking at things further away.
This blurred effect is due to incoming
light being focused behind, instead of
on, the retina wall due to insufficient
accommodation by the lens.

8. EYE – DEFECTS AND DISEASES
 Night blindness
The deficiency of Vitamin A results in the
low production of retinal.
This in turn prevents the resynthesis of
rhodopsin.
In this condition, objects cannot be seen
clearly in dim light and this disease is
called night blindness.

9. EYE – DEFECTS AND DISEASES
 Xerophthalmia
If there is a prolonged deficiency of
Vitamin A, the conjunctiva and
cornea become dry and opaque.
This causes xerophthalmia and
leads ultimately to blindness

10. EYE – DEFECTS AND DISEASES
 Colour Blindness
The retina contains cone cells which
can detect red, green and blue
colours.
Some persons cannot distinguish
green and red colours due to the
defect of cone cells.
This condition is called colour
blindness.

11. EYE – DEFECTS AND DISEASES
 Glaucoma
Aqueous humor is the fluid which
nourishes the tissues in the eyes.
If the reabsorption of aqueous humor
does not occur, it causes an increase in
the pressure inside the eyes.
This causes damage to the retina and
the photoreceptor cells and ultimately
leads to blindness.

12. EYE – DEFECTS AND DISEASES
 Cataract
It is a condition in which the lens of the
eyes become opaque resulting in blindness
 Conjunctivitis
This is an infection of the conjunctiva.
The causative organisms may be bacteria,
virus etc.
This disease is transmitted through contact
and can be prevented by maintaining
personal hygiene

13. OVERVIEW
1) Myopia
2) Hypermetropia
3) Night blindness
4) Xerophthalmia
5) Colour Blindness
6) Glaucoma
7) Cataract
8) Conjunctivitis

14. HOW TO KEEP YOUR EYES HEALTHY
 Eat well
 Quit smoking
 Wear sunglass
 Keep screens at a distance
 Visit your eye doctor