Structures of the Eye
|Figure 1: Structures of the eye|
Back of the Eye
The eye is a spherical structure. It is connected at its rear pole to the brain via the optic nerve. The optic nerve is a fibrous tube containing over one million horizontally running nerve fibers (axons), each one originating from a type of retinal cell called a ganglion cell. The retina and optic nerve are pictured in Figure 1.
The retina is composed of a thin sheet of cells (and related structures) that form the back wall of the eye. Its primary role is to capture light and transform it into electrical signals. The signals are transmitted to the brain by the optic nerve, where they are interpreted as the objects we “see.”
Ganglion cell axons are responsible for transmitting these electrical signals. The axons spread out across the retina to converge at the optic disc, the point of origin of the optic nerve. The optic disc is where damage from glaucoma is typically detected by an eye exam.
|Figure 2: Front of the eye|
Front of the Eye
When we look at our eyes in the mirror, we see four main features of the front of the eyeball: the white sclera, the black pupil, the colored iris, and the dome-shaped cornea overlaying the iris and pupil. In most cases of glaucoma, the trouble lies immediately behind the cornea in the outflow of a fluid called aqueous humor (or aqueous fluid). Normally, aqueous humor flows from behind the iris (posterior chamber), where it is formed, to the front of the iris (anterior chamber) where it drains through the trabecular meshwork into Schlemm's canal and ultimately into the blood circulation (Figure 2). Aqueous humor should not be confused with tears, which are formed outside the eye.