Healthcare and Medicine Reference
In-Depth Information
(Gram-negative bacilli) infection is associated with the use of contact
lens (Liesegang 1997). After the immediate adhesion of organisms to the
damaged epithelium, stromal invasion occurs rapidly within an hour. This
leads to a descemetocele and eventual perforation within 2 to 5 d of the onset
of infection. Klebsiella sp. , Escherichia coli , Proteus sp. (Gram-negative bacilli)
usually cause indolent ulcerations in previously compromised corneas.
Marginal keratitis (catarrhal ulcer) is a common condition caused by
a hypersensitivity reaction to staphylococcal exotoxins. It is particularly
common in patients suffering from chronic staphylococcal blepharitis
(Kanski 1994). The examination of early cases shows the presence of sub
epithelial infi ltrate in 10, 2, 4, or 8 o'clock peripheral corneal position
which is separated from the limbus by a clear zone of the cornea, and is
accompanied by a breakdown of the overlying epithelium.
Parasitic Keratitis
Acanthamoeba Keratitis (AK)
Acanthamoeba histolyticum is a free-living protozoan found in air, soil and
fresh or brackish waters that cause an infi ltrative corneal ulceration. They
exist in both active (trophozoite) and dormant (cystic) forms. The cystic
form is able to survive for long periods under hostile environmental
conditions, including chlorinated swimming pools, hot tubs and subfreezing
temperatures in fresh water lakes. The cysts turn into trophozoites, under
appropriate environmental conditions, which produce a variety of enzymes
that aid in tissue penetration and destruction (Panjwani 2010). Those using
contact lens are particularly at risk of acanthamoeba infection that may
be misdiagnosed and confused with herpetic or fungal infection
(Liesegang 1997).
Early diagnosis and appropriate therapy is a key to good prognosis.
A provisional diagnosis of acanthamoeba keratitis (AK) can be made
using the clinical features and confocal microscopy; although a defi nitive
diagnosis requires culture, histology, or identifi cation of the acanthamoeba
deoxyribonucleic acid by polymerase chain reaction.
Clinical Features: Symptoms and Signs
The main symptoms of AK are foreign body sensation, photophobia, and
severe pain (predominantly unilateral). Its signs are granular epithelial
irregularity with punctate or dendriform changes and stromal infi ltrates that
can ensue and gradually coalesce into a crescentic or annular confi guration.
With progression, coalescent dense suppurate necrosis may occur and
lead to ulceration and perforation. Corneal neovascularization is typically
absent.
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