Definition

Glaucoma is a group of eye diseases characterized by
damage to the optic nerve usually due to excessively high
intraocular pressure (IOP).This increased pressure within
the eye, if untreated can lead to optic nerve damage resulting
in progressive, permanent vision loss, starting with
unnoticeable blind spots at the edges of the field of vision,
progressing to tunnel vision, and then to blindness.

Description

Between two to three million people in the United
States have glaucoma, and 120,000 of those are legally
blind as a result. It is the leading cause of preventable
blindness in the United States and the most frequent
cause of blindness in African-Americans, who are at
about a three-fold higher risk of glaucoma than the rest
of the population. The risk of glaucoma increases dramatically
with age, but it can strike any age group, even
newborn infants and fetuses.

Glaucoma can be classified into two categories:
open-angle glaucoma and narrow-angle glaucoma. To
understand what glaucoma is and what these terms mean,
it is useful to understand eye structure.

Eyes are sphere-shaped. A tough, non-leaky protective
sheath (the sclera) covers the entire eye, except for
the clear cornea at the front and the optic nerve at the
back. Light comes into the eye through the cornea, then
passes through the lens, which focuses it onto the retina
(the innermost surface at the back of the eye). The rods
and cones of the retina transform the light energy into
electrical messages, which are transmitted to the brain by
the bundle of nerves known as the optic nerve.

The iris, the colored part of the eye shaped like a
round picture frame, is between the dome-shaped cornea
and the lens. It controls the amount of light that enters
the eye by opening and closing its central hole (pupil)
like the diaphragm in a camera. The iris, cornea, and lens
are bathed in a liquid called the aqueous humor, which is
somewhat similar to plasma. This liquid is continually
produced by nearby ciliary tissues and moved out of the
eye into the bloodstream by a system of drainage canals
(called the trabecular meshwork). The drainage area is
located in front of the iris, in the angle formed between
the iris and the point at which the iris appears to meet the
inside of the cornea.

Glaucoma occurs if the aqueous humor is not
removed rapidly enough or if it is made too rapidly, causing
pressure to build-up. The high pressure distorts the
shape of the optic nerve and destroys the nerve. Destroyed
nerve cells result in blind spots in places where the image
from the retina is not being transmitted to the brain.
Open-angle glaucoma accounts for over 90% of all
cases. It is called