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.

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.

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.

The round hole in the middle of iris is called pupil. Its diameter is 3-4 mm. It is surrounded by circular and areolar muscles. The pupil becomes smaller or larger due to muscle contraction and expansion. The pupil enlarges in dim light and shrinks in bright light. It controls light entering the eye.

The black screen formed by the choroid behind the cornea is called Iris. It is composed of the circular muscle and the areolar muscle. It dilates and dilates the pupil and ensures moderate light entry into the eye.

The ligaments surrounding the lens are called suspensory ligaments. One end of the ligament is attached to the lens and the other end to the ciliary body. The suspensory ligament changes the curvature of the lens through contraction and extension.

The thick part of the ring at the junction of iris and choroid is called ciliary body. It consists of ciliary ring, ciliary process and ciliary muscle.
Function of the ciliary body
(i) The ciliary muscle changes the shape of the lens by contraction-dilation and participates in accommodation.
(ii) It produces aqueous humor.

The second layer of eyeball is choroid. It is composed of blood vessels, muscle and melanin pigment. The parts of choroid are:
1. Ciliary body: The thick part of the ring at the junction of iris and choroid is called ciliary body. It consists of ciliary ring, ciliary process and ciliary muscle.
Function of the ciliary body
(i) The ciliary muscle changes the shape of the lens by contraction-dilation and participates in accommodation.
(ii) It produces aqueous humor.
2. Suspensory ligaments: The ligaments surrounding the lens are called suspensory ligaments. One end of the ligament is attached to the lens and the other end to the ciliary body. The suspensory ligament changes the curvature of the lens through contraction and extension.
3. Iris: The black screen formed by the choroid behind the cornea is called Iris. It is composed of the circular muscle and the areolar muscle. It dilates and dilates the pupil and ensures moderate light entry into the eye.
4. Pupil : The round hole in the middle of iris is called pupil. Its diameter is 3-4 mm. It is surrounded by circular and areolar muscles. The pupil becomes smaller or larger due to muscle contraction and expansion. The pupil enlarges in dim light and shrinks in bright light. It controls light entering the eye.

(i) Sclera gives shape to the eye.
(ii) Light enters through the cornea.
(iii) Conjunctiva protects the eye from dust and germs.

The outer layer of the eyeball is called sclera. It is colorless, opaque, hard and elastic. It is composed of cartilage and connective tissue. At the front of the eye, the sclera changes to form a very thin and transparent cornea. The cornea is called the window of the eye. There is no blood supply to the cornea. It receives nutrients from the aqueous humor. Outside the cornea is a thin and transparent conjunctiva. The part behind the sclera through which the optic nerve enters is called the lamina cribosa.