K

keratitis INFLAMMATIONof the CORNEA, usually the
result of anINFECTION. The cause of the infection is
more commonly viral, such as HERPES SIMPLEXor
HERPES ZOSTER, than bacterial. Symptoms of infec-
tious keratitis include

• redness and irritation of the EYEand conjunc-
  tiva (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 fol-
lows a CORNEAL INJURY, such as an abrasion or lac-
eration, and requires treatment with ophthalmic
ANTIBIOTIC MEDICATIONS. Chronic or recurrent ker-
atitis can cause permanent scarring of the cornea,
resulting in diminished visual acuity such as ASTIG-
MATISM. Extensive corneal damage may require
CORNEAL TRANSPLANTATION.
SUNBURNis the most common cause of noninfec-
tious keratitis. Extended exposure to the sun, espe-
cially on or around water, exposes the surface of
the eye to the same ultraviolet rays that cause sun-
burn of the SKIN. Ultraviolet burns to the cornea are
painful; treatment with ophthalmic CORTICOSTEROID
MEDICATIONShelps reduce the inflammation.
See also BACTERIA; CONJUNCTIVITIS; EPISCLERITIS;
IRITIS; SCLERITIS; SUN PROTECTION; UVEITIS; VIRUS.

keratoconus A degenerative disorder in which

the CORNEAthins, allowing it to protrude from the

surface of the EYEin somewhat of a cone shape.

Keratoconus affects both eyes though often pro-

gresses at different rates in each eye. Ophthalmol-

ogists 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(near-

sightedness) and ASTIGMATISM(distortions of vision

resulting from the irregular surface of the cornea).

As these REFRACTIVE ERRORSare the primary symp-

toms, 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 con-

tain 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 transplanta-

tion successfully restores vision in about 90 per-

cent 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 dif-

ferent thicknesses to allow less or more flattening

and are replaceable.

See also CORNEAL INJURY; CORRECTIVE LENSES.

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