The eyeball is a spherical organ that allows humans and many animals to see. It is made up of several parts, including the cornea, lens, retina, and iris. The cornea helps focus light, while the lens adjusts to help us see objects at different distances. The retina converts light into signals that are sent to the brain through the optic nerve. The iris is the colored part of the eye that controls the size of the pupil, which regulates the amount of light entering the eye. Proper functioning of the eyeball is essential for clear vision, and various conditions can affect its health, such as cataracts and glaucoma.