Parts of the Eye:There are five important parts of the eye; the cornea, pupil, lens, retina and iris. All of these parts need to work correctly for clear vision. The eye also has a blind spot, which is the point where the optic nerve enters the eye, rendering the area insensitive to light.

The cornea:

The cornea is the transparent, dome-shaped window covering the front of the eye. It is a powerful refracting surface, providing 2/3 of the eye's focusing power. Like the crystal on a watch, it gives us a clear window to look through.Cornea - eye anatomy. Because there are no blood vessels in the cornea, it is normally clear and has a shiny surface. The cornea is extremely sensitive - there are more nerve endings in the cornea than anywhere else in the body.

The adult cornea is only about 1/2 millimeter thick and is comprised of 5 layers: epithelium, Bowman's membrane, stroma, Descemet's membrane and the endothelium.

Because the cornea is as smooth and clear as glass but is strong and durable, it helps the eye in two ways:It helps to shield the rest of the eye from germs, dust, and other harmful matter. The cornea shares this

protective task with the eyelids, the eye socket, tears, and the sclera, or white part of the eye.

The cornea acts as the eye's outermost lens. It functions like a window that controls and focuses the entry of light into the eye. The cornea contributes between 65-75 percent of the eye's total focusing power.

When light strikes the cornea, it bends -- or refracts -- the incoming light onto the lens. The lens further refocuses that light onto the retina, a layer of light sensing cells lining the back of the eye that starts the translation of light into vision. For you to see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina. The retina converts the light rays into impulses that are sent through the optic nerve to the brain, which interprets them as images. The refractive process is similar to the way a camera takes a picture. The cornea and lens in the eye act as the camera lens. The retina is similar to the film. If the image is not focused properly, the film (or retina) receives a blurry image.

The cornea also serves as a filter, screening out some of the most damaging ultraviolet (UV) wavelengths in sunlight. Without this protection, the lens and the retina would be highly susceptible to injury from UV radiation.

The Iris :

The iris is in the anterior compartment at the front of the eye. It lies between the cornea and the crystalline lens. When looking at your eye, it appears as the colored disk but it is actually a thin diaphragm that is made up of a collection of muscle fibers and connective tissue. The iris is made up of three layers, which, from front to back, are the endothelium, the stroma, and the epithelium..

The iris acts as a divider between the large anterior chamber, which is between the iris and the cornea, and the small posterior chamber, located between the iris and the lens.

The eye can be compared to a camera. In this analogy, the iris and the pupil act like the aperture of the camera, with the iris functioning like the camera's shutter. At night, when less light enters the eye, the iris dilator muscle pulls outward from the center. This causes the pupil to get bigger, or dilate, allowing more light to enter the eye. Conversely, when there is a bright light, the iris sphincter muscle causes the pupil to become smaller (constrict) by pulling toward the center. This allows less light to enter the eye, preventing damage of the retina.

The iris also can be used to identify people, in a similar manner to a fingerprint, because the color, texture and pattern of every iris is unique.

The pupil :

The pupil is the opening in the center of the iris. The size of the pupil determines the amount of light that enters the eye. The pupil size is controlled by the dilator and sphincter muscles of the iris. Doctors often evaluate the reaction of pupils to light to determine a person's neurological function.

The Lens : The lens is located right behind the iris, the cornea, pupil, aqueous,conjunctiva, and the sclera. And it is in front of the vitreous..The lens of an eye is a clear convex disc that light passes through to focus on the retina in the back of the eye.It bends light waves, focusing them onto the retina on the back of the eye, where they are then sent as impulses along the optic nerve to the brain.

The lens is a little flexible bag of gel-like protein just behind your iris (the coloured part of the eye). It can change shape because around it is a doughnut-shaped muscle called the ciliary muscle. When this muscle contracts, it squeezes the lens, making it fatter. This reduces the focal length of the lens, which allows you to focus on closer objects. the; the front surface of the eye. The lens acts as a fine control to adjust the focusing

distance between close-up and distant. This adjustment process is called accommodation.

The Retina :The retina is a multi-layered sensory tissue that lines the back of the eye. It contains millions of photoreceptors that capture light rays and convert them into electrical impulses. These impulses travel along the optic nerve to the brain where they are turned into images.

There are approximately 125 million rods. They are spread throughout the peripheral retina and function best in dim lighting. The rods are responsible for peripheral and night vision.