Page 42 - JOP2020

Acanthamoeba Keratitis by the Numbers
Acanthamoeba keratitis was first discovered by
Nagington in 1974 in the United Kingdom and has
been recognized as a significant ocular microbial
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infection. It was first documented in the United States
soon afterward, when a farmer scratched his cor-
nea with wire and then washed out his damaged eye
with contaminated irrigation water. Diagnostic and
clinical information was limited until the 1980s until
it was determined that contact-lens wear increased
the chance of developing the infection. Studies have
shown significant increases in A. keratitis patients in
the United States, Australia, Italy, New Zealand, and
Brazil. Starting in the mid-1990s, the United States Figure 2. Corneal ring infiltrate.
saw a spike in the number of A. keratitis cases. There Photograph courtesy of Jesse M. Vislisel, M.D.
have been an estimated 5000 cases of the infection in
Photographer: Brice Critser, CRA (see reference number 6)
the United States as of 2006, but because A. keratitis
is commonly misdiagnosed and it is not required to
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be reported to the Centers for Disease Control and pends on what type of contact lens an individual uses.
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Prevention, the actual number could be much greater. Overnight-lens users are much more likely to develop
Developing nations in Asia and Africa have exception- A. keratitis. In contrast, daily disposable lenses are
ally high rates of infectious keratitis due to inadequate least likely to lead to an infection. Continuous-wear
community-water storage and treatment. silicone hydrogel lenses are also more prevalent to
Acanthamoeba attachment. Individuals who wear
Risk Factors Associated with Contracting rigid lenses are less prone to Acanthamoeba infections
A. Keratitis than those who wear soft lenses. Approximately 88%
Corneal trauma, ocular surgery, and contact-lens use of contact lens–related cases of A. keratitis cases occur
are all risk factors for the development of infectious among those who wear soft contact lenses and among
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keratitis. Greater than 85% of Acanthamoeba keratitis 12% of those who wear rigid lenses. Soft contact
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cases are associated with the use or abuse of wearing lenses act like a sponge with the amoeba being able
contact lenses. Multiple factors figure into this: to adhere to the lenses much easier than hard
(1) Contact-lens wear for extended periods of time, contact lenses.
(2) lack of personal hygiene, (3) inappropriate clean-
ing of contact lenses, (4) biofilm formation on contact Signs and Symptoms
lenses, (5) exposure to contaminated water or soil, There are many signs and symptoms of A. keratitis.
(6) swimming {especially while wearing contact lens- The most common symptom is eye pain, which can
es), (7) handling contact lenses without proper hand be severe. Vision impairment, photophobia, and the
washing, and (8) the use of homemade saline or even feeling of a foreign body in the eye are also common
chlorine-based disinfectants for contact lens cleaning. symptoms. The most distinctive clinical feature of
Fortunately, an intact cornea is highly resistant A. keratitis is a pronounced ring-like stromal infiltrate,
to A. Acanthamoeba infection. When the epithelial which is believed to be composed of inflammatory-
layers of the cornea are compromised, the door to cells (Figure 2). Other signs include redness of the eye
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Acanthamoeba infiltration is opened. This is easily and excessive tear production. If the infection is not
instituted by improper contact-lens fit and also from treated during its early stages, it can advance and ex-
over-wearing contact lenses. The contact lens can also hibit signs of scleritis. This can cause corneal inflam-
act as a physical pathway of transport for the parasite mation and conjunctival hyperemia. In severe cases,
from a contaminated source (such as a case or a bottle Acanthamoeba can spread to the retina and cause
of wetting solution) into the host’s eye. chorioretinitis. Restoring any useful visual acuity is
Contact lenses can also trap Acanthamoeba against limited at this late stage.
the cornea, which increases the chance of intrusion.
Susceptibility to Acanthamoeba infection also de-

40 | PATAKY JOURNAL OF OPHTHALMIC PROSTHETICS