Encyclopedia of Health and Medicine

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keratitis INFLAMMATION of the CORNEA, usually the
result of an INFECTION. The cause of the infection is
more commonly viral, such as HERPES SIMPLEX or
HERPES ZOSTER, than bacterial. Symptoms of infectious
keratitis include
• redness and irritation of the EYE and conjunctiva
(inner eyelids)
• discomfort or PAIN
• excessive tearing
• difficulty keeping the eye open
• diminished VISUAL ACUITY (usually blurred vision)
• eye discharge or crusting
Viral keratitis usually runs its course without
complication, though occasionally a secondary
bacterial infection may develop. ANTIVIRAL MEDICA-
TIONS sometimes shorten the course of chronic
herpes infections. Bacterial keratitis typically follows
a CORNEAL INJURY, such as an abrasion or laceration,
and requires treatment with ophthalmic
ANTIBIOTIC MEDICATIONS. Chronic or recurrent keratitis
can cause permanent scarring of the cornea,
resulting in diminished visual acuity such as ASTIG-
MATISM. Extensive corneal damage may require
CORNEAL TRANSPLANTATION.
SUNBURN is the most common cause of noninfectious
keratitis. Extended exposure to the sun, especially
on or around water, exposes the surface of
the eye to the same ultraviolet rays that cause sunburn
of the SKIN. Ultraviolet burns to the cornea are
painful; treatment with ophthalmic CORTICOSTEROID
MEDICATIONS helps reduce the inflammation.
See also BACTERIA; CONJUNCTIVITIS; EPISCLERITIS;
IRITIS; SCLERITIS; SUN PROTECTION; UVEITIS; VIRUS.
keratoconus A degenerative disorder in which
the CORNEA thins, allowing it to protrude from the
surface of the EYE in somewhat of a cone shape.
Keratoconus affects both eyes though often progresses
at different rates in each eye. Ophthalmologists
do not know what causes keratoconus,
though it appears to run in families. Keratoconus
is painless though results in progressive VISION
IMPAIRMENT, typically in the forms of MYOPIA (nearsightedness)
and ASTIGMATISM (distortions of vision
resulting from the irregular surface of the cornea).
As these REFRACTIVE ERRORS are the primary symptoms,
the keratoconus may not become apparent
until the coning becomes obvious.
Treatment for mild to moderate keratoconus is
rigid gas-permeable contact lenses, which correct
the refractive errors of vision as well as help contain
the shape of the cornea. As the keratoconus
progresses, however, contact lenses become less
effective, and the thinned cornea may not be able
to tolerate them. Keratoconus ultimately destroys
the cornea and is a leading reason for CORNEAL
TRANSPLANTATION, which replaces the diseased
cornea with a donor cornea. Corneal transplantation
successfully restores vision in about 90 percent
of people who have keratoconus and
undergo the procedure.
In 2004 the US Food and Drug Administration
(FDA) approved a new treatment for keratoconus,
corneal inserts, which are tiny plastic rings the
ophthalmologist implants along the edge of the
cornea. The corneal inserts flatten the cornea,
reducing the coning. Corneal inserts come in different
thicknesses to allow less or more flattening
and are replaceable.
See also CORNEAL INJURY; CORRECTIVE LENSES.
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