C h a p t e r 3 8
Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function
959
Corneal Trauma
The integrity of the epithelium and endothelium is
necessary to maintain hydration of the cornea within a
limited range.
8
The integrity of the endothelium is more
important than the epithelium, and damage to the endo-
thelial cells is far more serious, causing edema of the
cornea and loss of transparency. With corneal edema,
the cornea appears dull, uneven, and hazy; visual acuity
decreases; and iridescent vision (i.e., rainbows around
lights) occurs.
Trauma that causes abrasions of the cornea can be
extremely painful, but if minor, the abrasions usually
heal in a few days. The epithelial layer can regenerate,
and small defects heal without scarring. If the stroma is
damaged, healing occurs more slowly, and the danger
of infection is increased. Injuries to the Bowman mem-
brane and the stromal layer heal with scar formation
that impairs the transmission of light.
Keratitis
Keratitis
, or inflammation of the cornea, can be caused
by infections, misuse of contact lenses, hypersensitiv-
ity reactions, ischemia, trauma, defects in tearing, and
interruption in sensory innervation, as occurs with local
anesthesia. Scar tissue formation due to keratitis is the
leading cause of blindness and impaired vision through-
out the world. Most of this vision loss is preventable if
the condition is diagnosed early and appropriate treat-
ment is begun.
Keratitis can be infectious or noninfectious and non-
ulcerative or ulcerative.
8,9
In
nonulcerative
keratitis, all
the layers of the epithelium may be affected, but the epi-
thelium remains intact. There are a number of causes of
epithelial keratitis, including epidemic keratoconjuncti-
vitis caused by adenoviruses 8 and 19 and ultraviolet
(UV) light exposure. Most cases of UV keratitis occur
in welders with inadequate eye protection, but may also
occur with tanning booth and other UV lamp exposure,
and from sun reflecting off snow.
10
Ulcerative keratitis
is an inflammatory process in
which parts of the corneal epithelium, stroma, or both
are destroyed. Causes of ulcerative keratitis include
infectious agents (e.g.,
S. aureus, S. pneumoniae, C. tra-
chomatis
), exposure trauma, and use of extended-wear
contact lenses (i.e.,
Pseudomonas
and
Acanthamoeba
keratitis). Bacterial keratitis is aggressive and demands
immediate care.
Mooren ulcer
is a chronic, indolent, but
painful ulcerative keratitis that occurs in the absence of
infection. It is usually seen in older persons and may
affect both eyes. Although the cause is unknown, an
autoimmune origin is suspected.
Herpes Simplex Keratitis.
Herpes simplex virus (HSV)
keratitis, which usually is unilateral, is an important
cause of ocular morbidity.
11,12
With the exception of neo-
natal infections, which are usually due to HSV type 2
(genital herpes) acquired during the birth process, most
cases of herpes keratitis are caused by HSV type 1 (labial
[lip] herpes). The disease can occur as either a primary or
recurrent infection. Primary epithelial infections are the
optical counterpart of labial herpes with similar immu-
nologic and pathologic features as well as a similar time
course (see Chapter 46).
The first manifestations of recurrent herpes keratitis
are irritation, photophobia, and tearing. Some reduc-
tion in vision may occur when the lesion affects the
central part of the cornea. Because corneal anesthesia
occurs early in the disease, the symptoms may be mini-
mal. A history of fever blisters or other herpetic infec-
tion is often noted, but corneal lesions may be the only
sign of recurrent herpes infection. Typically, the corneal
lesions involve the epithelium and heal without scarring.
Lesions that involve the stromal layer of the cornea pro-
duce increasingly severe corneal opacities.
Any person with herpes simplex keratitis and an acute
red eye should be referred urgently to an ophthalmolo-
gist. The treatment of HSV keratitis includes the use of
topical antiviral agents to promote healing.
8
Oral antivi-
ral agents (e.g., acyclovir) may be helpful for treatment
of severe keratitis and as prophylaxis against recurrence,
particularly in persons with compromised immune func-
tion. Although corticosteroids may control the damag-
ing inflammatory responses, they do so at the expense of
facilitating viral replication. With a few exceptions, their
use is contraindicated.
11
Varicella Zoster Ophthalmicus.
Herpes zoster or
shingles
is a relatively common infection due to the her-
pesvirus that causes varicella (chickenpox).
8,12
Herpes
ophthalmicus, which represents 10% to 25% of all cases
of herpes zoster, occurs when reactivation of the latent
virus occurs in the ganglia of the ophthalmic division of
the trigeminal nerve.
12
Immunocompromised persons,
particularly those with human immunodeficiency virus
(HIV) infection, are at higher risk for developing herpes
zoster ophthalmicus than those with a normally func-
tioning immune system.
Herpes zoster ophthalmicus usually presents with
malaise, fever, headache, and burning and itching of the
periorbital area. These symptoms commonly precede
the ocular eruption by a day or two. The rash, which
is initially vesicular, becomes pustular and then crusting
(see Chapter 46). Involvement of the tip of the nose and
lid margins indicates a high likelihood of ocular involve-
ment. Ocular signs include conjunctivitis, keratitis, and
anterior uveitis, often with elevated intraocular pres-
sure. Persons with corneal disease present with varying
degrees of decreased vision, pain, and sensitivity to light.
Treatment includes the use of oral and intravenous
antiviral drugs. Initiation of treatment within the first
72 hours after the appearance of the rash reduces the inci-
dence of ocular complications but not the postherpetic
neuralgia
8
(see Chapter 35). Many cases of herpes zoster
and herpes zoster ophthalmicus can now be prevented
with the herpes zoster vaccine.
Acanthamoeba Keratitis.
Acanthamoeba
is a free-
living cyst-forming protozoan that thrives in polluted
water containing bacteria and organic material.
8,13,14
Acanthamoeba
keratitis is a rare but sight-threatening
complication that typically occurs in people who wear
