List the parts of the human eye that control the amount of light entering into it. Explain how they perform this function

(a) List the parts of the human eye that control the amount of light entering into it. Explain how they perform this function.
(b) Write the function of retina in human eye.
© Do you know that the corneal-impairment
can be cured by replacing the defective cornea with the cornea of the donated eye? How and why should we organise groups to motivate the community members to donate their eyes after death?

(a) The parts are iris and pupil. Between the cornea and the lens we have a muscular coloured diaphragm called iris, which has a small hole in it, called the pupil. Iris is the coloured part that we see in the eye. The size of the pupil varies with the help of iris. In dim light, the size of the pupil increases with the help of iris to allow more light to enter the eye. In bright light,-the pupil contracts to allow less light to enter into the eye. In other words, the iris regulates the amount of light entering the eye by dilating the pupil in light of low intensity and contracting the pupil in high-intensity light.
(b) The innermost coating of the eye, covering the rear of inner surface is the retina. It is the screen on which the image is formed by the eye lens. Retina contains a large number of nerve fibres and blood vessels and act as a light sensitive screen to receive the images. The light sensitive cells get activated upon illumination and generate electrical signals. The sensation of vision in the retina is carried to the brain by optic nerve fibres, which are more than one million.
© About 35 million people in the developing world are blind and most of them can be cured. About 4.5 million people with corneal blindness can be cured through corneal transplantation of donated eyes. Out of these 4.5 million, 60% are children below the age of 12. So, if we have got the gift of vision, why not pass it on to somebody who does not have it. People can be motivated to donate their eyes
after death by telling them about this good deed. They can be told that they will live in someone else body even after their death. For this awareness camps can be organised to tell the people about the benefits they will give to the blind.