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“Glaucoma,” a Principal Cause of Blindness. Glaucoma is one
of the most common causes of blindness. It is a disease
of the eye in which the intraocular pressure becomes
pathologically high, sometimes rising acutely to 60 to
70 mm Hg. Pressures above 25 to 30 mm Hg can cause
loss of vision when maintained for long periods.
Extremely high pressures can cause blindness within
days or even hours. As the pressure rises, the axons of
the optic nerve are compressed where they leave the
eyeball at the optic disc.This compression is believed to
block axonal flow of cytoplasm from the retinal neuronal
cell bodies into the optic nerve fibers leading to
the brain. The result is lack of appropriate nutrition of
the fibers, which eventually causes death of the involved
fibers. It is possible that compression of the retinal
artery, which enters the eyeball at the optic disc, also
adds to the neuronal damage by reducing nutrition to
the retina.
In most cases of glaucoma, the abnormally high pressure
results from increased resistance to fluid outflow
through the trabecular spaces into the canal of Schlemm
at the iridocorneal junction. For instance, in acute
eye inflammation, white blood cells and tissue debris
can block these trabecular spaces and cause an acute
increase in intraocular pressure. In chronic conditions,
especially in older individuals, fibrous occlusion of the
trabecular spaces appears to be the likely culprit.
Glaucoma can sometimes be treated by placing drops
in the eye that contain a drug that diffuses into the
eyeball and reduces the secretion or increases the
absorption of aqueous humor.When drug therapy fails,
operative techniques to open the spaces of the trabeculae
or to make channels to allow fluid to flow directly
from the fluid space of the eyeball into the subconjunctival
space outside the eyeball can often effectively
reduce the pressure.

Glaucoma is a condition of increased fluid pressure inside the eye. The increased pressure causes compression of the retina and the optic nerve which can eventually lead to nerve damage. Glaucoma can cause partial vision loss, with blindness as a possible eventual outcome.