Tropical Medicine 8: Ocular Manifestations
River Blindness
Onchocerciasisis
is also known as River Blindness. The
same migrating larvae
that causes the skin lesions also migrate through the eye and may cause
disease
in the anterior (punctuate keratitis, pannus, iritis) and posterior
(chorioretinitis, optic atrophy) chambers, all of which lead to
vision loss. Diagnosis is by skin
snip or serology; additionally, use of the slit lamp may reveal
microfilariae in the
anterior chamber. Treatment is use of ivermectin. (Vol III—TM5 Dermatological Manifestations)
Loaiasis
A worm related to Onchocerca is
Loa Loa. Spread by the bite of the deer fly, this
worm lives in subcutaneous tissues
and continually migrates through them, unlike the female
Onchocerca, which reside in
nodules. Loa also sheds
microfilariae, but they migrate through the blood, whereas
Onchocerca’s larvae
migrate through the subcutaneous tissues. Clinically, loaiasis is manifest by
transient swellings, known as Calabar swellings, and by the migration of the
adult worm through the conjunctivae (which is pathognomonic). Diagnosis is
definitive when the adult worm or microfilariae are identified; serology may be
helpful. Treatment employs albendazole or ivermectin.(Vol III—TM13 Antiparasitic Primer)
Acanthamoebae
Ordinarily a free-living amoeba, Acanthamoeba may cause a severe
keratoconjunctivitis. It
is more common in individuals who wear contact lenses. Clinically, it presents as a foreign body sensation which
may progress to an
impressive conjunctivitis with recurrent ulcerations, photophobia, and blurry
vision. Untreated, it may result in vision loss. Diagnosis is identification of the
amoeba or its cysts in conjunctival scrapings or biopsy.
Treatment is chlorhexidine 0.02% drops combined with propamidine 0.1% drops. Other agents may also be used, including topical polyhexamethylene biguanide (Baquacil®, ReNu®), aminoglycosides, propamidine isethionate, hexamidine diisethionate (Desomedine®), miconazole, Neosporin, or oral ketoconazole or itraconazole. A multidrug regimen greatly improves effectiveness and is recommended.
Occasionally, this organism may cause encephalitis similar to Naegleria, though ocular involvement does not appear to predispose to this.
Miscellaneous
Infections that involve
other locations may also be found in the eyes, including
cysticercosis, larval migrans, and toxoplasmosis. In addition, there is an
increased incidence of Chlamydia and
Neisseria in conjunctivitis in the tropics. These can
be potentially blinding, and should be treated accordingly.