The human eye, the organ of sight, is similar to a camera. Just like a camera, the eye has many distinct parts that must function together as a whole, to produce clear vision. The eye converts light into an electrical signal. The optic nerve transmits that signal to the brain. The brain converts this electrical signal into an image.
Cornea
When light enters the eye; it initially encounters the tear film. The tear film coats the cornea, the crystal clear window of the eye. Inadequate tear production can cause dry eye. Located behind the cornea is the anterior chamber, which is filled with fluid called the aqueous. This clear fluid is responsible for maintaining eye pressure. Any trouble with the drainage or production of the aqueous can lead to high pressure within the eye and glaucoma.
Iris
The iris is located inside the anterior chamber. The iris is responsible for eye color and acts like the diaphragm of a camera. It widens and narrows the pupil to enable more or less light to come into the eye.
Lens
After the iris, light next enters lens. The lens focuses light onto the retina. The lens changes shape slightly so that we can change focus when viewing objects that are near or far. As we get older, the flexibility of the lens decreases, and we become less able to change focus. This condition is known as presbyopia. Ultimately, the lens loses its clarity and may turn yellow or become cloudy. This condition is called a cataract. When cataracts cause blurry vision, dull colors or other symptoms, the lens can be replaced with an artificial lens.
Vitreous
After the lens, light passes through the vitreous, the jelly-like substance that fills the body of the eye. In younger years, the vitreous is firmly attached to the retina. As we get older, the vitreous becomes watery and can detach from the retina. In most cases, little strands or clusters of jelly form, and cast shadows, which are called floaters. Floaters are usually not a threat to vision, but they can signal a more serious condition, such as a retinal tear or detachment.
Retina
Lastly light enters the retina. The retina is the thin tissue that lines the innermost wall of the eye. The retina contains several layers that play a different role. The retina functions much like camera film. It responds to light rays by converting light into electrical signals. The optic nerve carries these signals to the brain. The outer part of the retina is responsible for peripheral vision, while the center portion, the macula is responsible for central and color vision. In the center of the macula is the fovea. The fovea consists of a high concentration of special cells known as cones, making it the only part of the eye capable of 20/20 vision. Any disease that affects the macula reduces central vision.
Optic Nerve
The optic nerve takes the electrical signals from the retina and transports it to the brain. The brain interprets these signals into a visual image. With glaucoma, the optic nerve becomes damaged due to high pressure in the eye.