G

glaucoma A serious and progressive EYEcondi-
tion in which the cells at the front of the OPTIC
NERVEwhere it intersects with the RETINA, the reti-
nal ganglia, die, resulting in vision loss. Early diag-
nosis and treatment can minimize vision loss.
Health experts estimate that 5 million Americans
have glaucoma, though only about 2 million of
them know it. Glaucoma is the third-leading cause
of blindness in the United States, primarily
because it remains undetected until damage to the
optic NERVE becomes significant. Glaucoma
becomes more common after age 65, though there
is a congenital form that manifests in early child-
hood (congenital glaucoma).
Until the late 1990s ophthalmologists perceived
glaucoma to be the exclusive consequence of
increased pressure within the eye (INTRAOCULAR
PRESSURE) that caused the death of retinal ganglia
cells. Current understanding of the disease process
of glaucoma affirms the death of retinal ganglia
cells as the cause of damage to the optic nerve,
though recognizes that numerous factors, intraoc-
ular pressure being only one among them, con-
tribute to this damage. About 30 percent of people
who have glaucoma have normal intraocular pres-
sure, and only about 10 percent of people who
have elevated intraocular pressure have glaucoma.
There are two general forms of glaucoma: open
angle and closed angle (also called angle-closure).
The designations refer to whether the channel
through which aqueous humor drains from the
eye, called the angle, is open but dysfunctional
(open-angle glaucoma) or becomes blocked by the
iris (closed-angle glaucoma). In glaucoma, the
drainage angle either malfunctions (open-angle
glaucoma) or a segment of the iris seals over it
(closed-angle glaucoma). When the aqueous
humor cannot properly drain, it causes the pres-

sure to increase in the anterior chamber. Increased

pressure in the chambers puts increased pressure

on the inner eye, causing intraocular pressure to

rise. Extreme or extended elevations in intraocu-

lar pressure compress the optic disk, causing nerve

cells to die.

Acute closed-angle glaucoma requires

emergency medical attention. Without

immediate treatment, severe to com-

plete vision loss can occur within hours

of the onset of symptoms.

Open-angle glaucoma is chronic, progressing

over years, and is the most common form of glau-

coma, accounting for about 85 percent. Closed-

angle glaucoma can be acute, with the sudden

onset of severe symptoms, or chronic with symp-

toms similar to those of open-angle glaucoma. The

function and dysfunction of aqueous humor

drainage is the dimension of glaucoma doctors

and researchers understand most clearly, and most

treatment approaches target reducing aqueous

humor production or improving its drainage from

the eye. Less clear are the other factors that con-

tribute to death of the retinal ganglia cells and cor-

responding destruction of the optic disk. These

factors are especially significant for the 30 percent

of people who have glaucoma with normal

intraocular pressure. Researchers are investigating

the roles of genetics, autoimmune processes, and

correlations with conditions such as DIABETESand

HYPERTENSION(highBLOOD PRESSURE).

Symptoms and Diagnostic Path

The key symptom of chronic glaucoma, open-

angle or closed-angle, is the gradual and painless

loss of VISUAL ACUITYand VISUAL FIELD. Often the

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