I

intraocular pressure The pressure within the EYE
that maintains the eye’s form and structure. Nor-
mal intraocular pressure in an adult is 12 to 22
millimeters of mercury (mm Hg). A device called a
tonometer measures intraocular pressure, either
through light contact against the anesthetized eye
or via the force of resistance to a puff of air blown
against the eye’s surface (a noncontact method
that does not require anesthetic drops). Elevated
intraocular pressure is called ocular hypertension.
Lower than normal intraocular pressure is called
ocular hypotension.
Ocular hypertension (greater than 21 mm Hg)
is a hallmark sign of GLAUCOMA, an eye condition
that, if untreated, results in complete loss of
vision. Other health conditions that can increase
intraocular pressure include tumors that press
against the eye, ORBITAL CELLULITIS, and GRAVES’S
OPHTHALMOPATHY. Increased intraocular pressure
damages the cells on the front of the OPTIC NERVE
(the retinal ganglia), leading to permanent VISION
IMPAIRMENT. Ophthalmic medications that reduce
intraocular pressure work through various mecha-
nisms, depending on the cause of the increased
pressure.
Ocular hypotension, in which the intraocular
pressure is lower than normal (less than 12 mm
Hg), characterizes chronic UVEITIS(INFLAMMATIONof
the structures of the eye) and of certain tumors of
the eye. Ocular hypotension also sometimes
accompanies systemic HYPOTENSION (low BLOOD
PRESSURE) and as a SIDE EFFECT of medications,
notably general anesthesia agents.
See also OPHTHALMIC EXAMINATION; TONOMETRY;
VITRECTOMY; VITREOUS DETACHMENT.

iritis INFLAMMATION of the iris, the MUSCLEsur-
rounding the pupil of the EYE. Iritis may develop

as a result of INFECTION, such as CONJUNCTIVITISthat

spreads to involve other structures of the eye. Iri-

tis also occurs as part of the inflammatory process

in AUTOIMMUNE DISORDERS such as RHEUMATOID

ARTHRITIS. The symptoms of iritis include

• irritation and a “gritty” sensation in the eye


• redness of the eye


• PHOTOPHOBIA(sensitivity to bright light)


• blurry vision


• excessive tearing

The ophthalmologist can diagnose iritis based

on the appearance of the iris and the eye, though

will additionally perform a SLIT LAMP EXAMINATION

to look for involvement of other structures of the

eye. Treatment is ophthalmic ANTIBIOTIC MEDICA-

TIONS(eye drops or ointment) when the ophthal-

mologist suspects bacterial infection and

ophthalmic CORTICOSTEROID MEDICATIONSto reduce

the inflammation. When the cause of the inflam-

mation is systemic, the ophthalmologist may pre-

scribe anti-inflammatory medications such as

corticosteroids or NONSTEROIDAL ANTI-INFLAMMATORY

DRUGS (NSAIDS). Treatment usually resolves the

symptoms without residual VISION IMPAIRMENT.

Untreated or recurrent iritis can have long-lasting

effects on vision, including increased INTRAOCULAR

PRESSURE.

See also BACTERIA; EPISCLERITIS; GLAUCOMA; KER-

ATITIS; SCLERITIS; UVEITIS.

ischemic optic neuropathy Damage to the OPTIC

NERVE resulting from insufficient blood supply,

sometimes called “STROKE” of the optic nerve.

Ischemic optic neuropathy is occurs most com-

monly in people over age 55 and causes mild to

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