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.