Anatomy of the Eye
Light passes through several structures before reaching the retina, which lines the inner wall at the back of the eye. The cornea forms the front window into the eye. The anterior chamber of the eye is filled with a fluid, the aqueous humor, which separates the cornea from the lens. The eye is constantly producing aqueous humor, which maintains the pressure inside the eye. This fluid drains in the anterior chamber angle, where the iris and cornea meet. Abnormalities of aqueous fluid production or drainage can lead to glaucoma. The iris is a pigmented tissue which is responsible for one's eye color. Small muscles in the iris affect the size of the pupil, the central dark opening in the iris through which light passes.
The lens helps to focus light on the retina. With age, the lens hardens, affecting its ability to change focusing power, and resulting in the need for reading glasses or bifocals. A cloudy lens is called a cataract.
The vitreous humor is a gel-like substance which fills the large central chamber of the eye. It is attached to the retinal surface.
All these structures must be clear to allow proper image formation on the retina, and various conditions can affect that clarity. The retina is a thin sheet of nerve tissue which translates images into electrical signals, and sends them to the brain via the optic nerve. The central part of the retina, which lies at the very back of the eye, is referred to as the macula. This area is responsible for good central vision. The choroid is a vascular layer which lies behind and supports the retina, and it plays a role in many retinal diseases.
