 Dear students, in this topic we shall discuss the structural physiology of vertebrate eye. Eye has different components which are involved in focusing and image formation. These parts include the cornea, a biconvex lens, a pupil, an iris and the retina. We shall discuss the roles of these parts in detail. First we shall discuss the role of cornea. Cornea is the clear outer surface of the eye. Light enters the eye through this cornea. Its function is to bend and focus light rays onto the lens. Cornea light receives light and bends it and focuses on the lens of the eye. 85% of the total refaction that occurs in the eye occurs here by the cornea. Now we shall discuss the role of pupil. The entry of light in the eye is controlled by increase or decrease in the diameter of the pupil. This control on the diameter of pupil is due to the circular smooth muscle fibers in the iris that encircles the pupil and controls the diameter of pupil. Now we shall discuss the role of lens. Lens focuses light rays on retina. All light rays are finally focused on retina. For this, light rays are bent, refracted and finally the image is focused on retina. Lens plays an important role in focusing on retina. The thickness of retina is changed. This change happens because of the suspensory ligaments, which are called fibres of zoniola and attack the ciliary muscles. This increases and decreases the thickness of the lens. As a result, light rays focus on retina. Now we shall discuss the role of fibres of zoniola and ciliary muscles. The fibres of zoniola held the lens in its place and they also change the shape of the lens by exerting an outward tension on the perimeter. This increases the pressure and force on the sides of the lens to reduce the thickness of the lens. These fibres of zoniola are not actually contractile. In fact, they are attached to the ciliary muscles. Actually, they are the contractile and they contract and pull the fibres of zoniola. When fibres of zoniola pull, they flatten the lens. Lens's flattening causes the distant objects to be focused on retina. However, when they relax, then lens becomes rounded. As a result, near objects are focused. Dear students, now we shall discuss the role of retina. Retina is the sensory layer of the eye which has photoreceptor cells known as rods and cones. The rods and cones are the cells which transduce photons of light into the nerve impulse. From retina, the impulses are carried by the optic nerve to the brain.