What Causes Glaucoma ?
Elevated pressure in the eye is the main factor leading to glaucomatous damage to the eye (optic) nerve. The optic nerve, which is located in back of the eye, is the main seeing nerve for the eye. This nerve transmits the images we see back to the brain for interpretation. The eye is firm and round, like a basketball. Its tone and shape are maintained by a pressure within the eye (the intraocular pressure), which normally ranges between 8 and 22 mm (millimeters) of mercury. When the pressure is too low, the eye becomes softer, while a too high pressure causes the eye to become harder. It turns out that the optic nerve is the most susceptible part of the eye to high pressure because the delicate fibers in this nerve are easily damaged.
The front of the eye is filled with a clear
fluid called the
aqueous humor, which provides nourishment to the structures
in the front of the eye. This fluid is produced constantly by
the ciliary body, which surrounds the lens of the eye. The
aqueous humor then flows through the pupil and leaves the eye
through tiny channels called the trabecular meshwork. These
channels are located at what is called the filtering, or
drainage angle of the eye. This angle is where the clear cornea,
which covers the front of the eye, attaches to the base (root or
periphery) of the iris, which is the colored part of the eye.
The cornea covers the iris and the pupil, which are in front of
the lens. The pupil is the small, round, black-appearing opening
in the center of the iris. Light passes through the pupil, on
through the lens, and to the retina at the back of the eye.
Please see the figure, which is a diagram that shows the
filtering angle of the eye.
This diagram of the front part of the eye is in cross section to show the filtering, or drainage angle. This angle is between the cornea and the iris, which join each other right where the drainage channels (trabecular meshwork) are located. The arrow shows the flow of the aqueous fluid from the ciliary body, through the pupil, and into the drainage channels. This figure is recreated from Understanding and Treating Glaucoma, a human anatomy board book by Tim Peters and Company Inc., Gladstone N.J.