The innermost layer of the eyeball is called retina. It is the only light sensitive part. It consists of 10 sub-layers. The outer layers are composed of pigment cells and the inner layers are composed of nerve cells. It contains two types of pigment cells. Rod cells and angle cells. Rod cells are elongated and cylindrical and suitable for dim light vision. Corneal cells are convex and suitable for vision in bright light.
1. Blind spot: There is a circular area in the retina devoid of rod cells and angle cells, called the optic disc. It is not light sensitive. It is called blind spot because no reflection is formed.
2. Fovea centralis: Above the optic disc in the retina is an oval and yellow area, called the macula lutea. The small hole in the center of the macula lutea is called the phobia centralis or yellow spot. It has very few rod cells and a lot of angle cells, so the best reflection is formed.
3. Optic nerve: Retina contains optic nerve. It sends signals to the brain.
Retina function
(i) Retina produces reflections.
(ii) The bile duct forms a clear reflex.
(iii) The optic nerve sends messages to the brain.