1. THE HUMAN EYE Gives the sense of sight. Allows us to learn more
Sense organ
Gives the sense of sight.
Allows us to learn more
about the surrounding
world.

2. Topics covered Eye Structure Functions Image formation Eye Defects
Correction of the Defects

3. External Appearance of the Eye

4. Functions Eye Lids: Cover and protect the eye by closing.
Regular blinking distributes fluid over the eye.
Prevent the eye from drying.
Pupil:
Determines the amount of light entering the eye.
Sclera:
Tough non elastic fibrous coat round the eye ball.
Iris:
Contracts or dilates to alter the pupil’s size.

5. The Structure of the Eye

6. Functions Cornea: Causes light to refract at the surface of the eye.
Lens:
It’s a converging lens.
Curvature is controlled by ciliary muscles and
suspensory ligaments.
Causes light to undergo further refraction.
Conjunctiva:
Transparent membrane.
Covers the sclera and lines the insides of the
eyelids.

7. Choroid:
Layer rich in blood vessels.
Supply the eye tissues with oxygen and nutrients.
Retina:
Projection screen at the back where the images
are focused.
Once focused, vision is good.
Optical nerve:
Carries the signal from the retina to the brain.
Cause of the blind spot in eyes.

8. Vitreous:
Transparent gel.
Fills the main cavity of the eye.
Macula:
A depression in the retina
cones (photoreceptor cells) are concentrated
and vision is most acute.

9. Image formation

10. Process of sight When you look at an object,
The light rays are bent, refracted and focused by
the cornea, lens, and vitreous.
The lens makes the rays come to a sharp focus on
the retina.
The resulting image on the retina is inverted,
diminished and real.
The light rays are converted to electrical impulses
which are then transmitted through the optic nerve,
to the brain, where the image is translated and
perceived in an upright position!

11. Short sightedness This person can’t see Causes: far things clearly
because light rays meet
in front of the retina.
Causes:
eye ball is too long.
eye lens is too strong.
cornea is too thick.

12. Correction of Short sightedness
The person should put on glasses with
concave (diverging) lenses so as to focus
far objects.

13. Long Sightedness This person can’t see near things clearly
because light rays meet
behind of the retina
Causes:
eye ball is too short.
eye lens is too weak.
cornea is too thin.

14. Correction of Long sightedness
The person should put on glasses with
convex (converging) lenses so as to focus
near objects.