0a. Cornea: The cornea is the outermost layer of the eye and is primarily responsible for focusing the light that comes into our eyes. The cornea provides 66% of the optic power that the overall eye has. This means that the cornea is very important in focusing what we see by bending light. There are 5 layers to the cornea. The outer layer acts as a kind of shield to the elements and can usually repair itself within a few days of suffering a minor injury. The deeper layers exist mainly to strengthen the eye.
b. Iris: The iris is the colored part of the eye. Although it might seem purely cosmetic, the iris actually functions to adjust the size of the pupil. It has muscles that contract or expand depending on the amount of light the pupil needs to process images.
c. Pupil: The pupil is the black circle in the center of the eye, and its primary function is to monitor the amount of light that comes into the eye. When there is a lot of light, the pupil contracts to keep the light from overwhelming the eye. When there is very little light, the pupil expands so it can soak up as much as possible.
d. Ciliary muscles: The focal length of the eye-lens can be changed by changing its shape by the action of ciliary muscles.
e. Eye-lens: This is a convex lens which is composed of a fibrous, jelly like material.
The nature of Image formed by eye lens: Real and inverted.
The curvature of eye lens is modified to some extent by the ciliary muscles. This change in the curvature of eye lens can thus change its focal length.
Increasing in focal length: When the ciliary muscles are relaxed, the lens becomes thin. This causes its focal length increases. This enables us to see distant objects clearly.
Decreasing in focal length: When we looking at closer objects, the ciliary muscles contract. This increases the curvature of the eye lens. This causes eye lens thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly.
f. Retina: The retina is the area at the back of the eye that receives the refined, visual message from the front of the eye, and it transmits that visual message to the brain using electrical signals. It is a delicate membrane having a large number of light sensitive cells called ‘rods’ and ‘cones’ which respond to the intensity of light and color of objects respectively.
g. Optic nerve: It conveys the image formed on the retina to the brain.
