Tropical

Ophthalmology. Part Three of Three

Dr. Steve WallerUniformed Services

University

of Health Sciences

Bethesda, Maryland, USAstephen.waller@usuhs.mil

Unusual tropical eye diseases

• Not commonly found in U.S., even in teaching hospitals

• Five examples:– atypical tuberculosis (TB)– leprosy– manzanillo keratopathy– loa loa conjunctivitis– tarantula keratopathy

Atypical TB– after LASIK or transplant, steroid gtts

– incidence resurging

Leprosy

• neurotrophic cornea• entropion• can have uveitis in

lepromatous disease

Manzanillo tree sap keratopathy• Manzanillo or “beach apple” tree

– common to Caribbean, east coast of Florida• Sap is milky latex vesicant known for delayed

dermal effects; folk medicine for conjunctivitis• Acute ocular effects first described in US

troops during WWII• Other natural blistering agents:

– cantharidine (beetle) – no known antidote– poison ivy/oak– podophyllum (mandrake root)

case seen in

military hospital

in San Antonio

Vesicant toxicity to cornea

Mustard gas: alkylation– crosslinks DNA and denatures protein

– clinical effect: • cornea edema• ischemia• secondary melt

or ulcer

World War I scene, France

Loa loa: the “eye worm”• Filarial nematode of West and Central Africa• mango fly (Chrysops), bites at dawn/dusk• 20 million infected, >30% in hyperendemic areas• adult worms live for 20 years, up to 60 mm long • subcutaneous or subconjunctival migration• “Calabar swelling” from allergic angioedema (named for eastern Nigeria seaport)

Manifestationsand life cycle

• pruritis, skin tracks• fever• meningitis• larvae travel in vessels• mango fly stages• 1-4 years to mature

Prevention, Diagnosis, Treatment

• Prevention: avoid vector contact, apply insecticide to mango groves

• Diagnosis: clinical or find microfilariae on Wright or Giemsa stains of daytime blood

• Treatment: surgery, ivermectin*, albendazole*, mebendazole*

* off label use

Excision of subconjunctival

loa loa worm

Tarantula keratopathy

• Uriticating hairs - dorsal abdomen

• ‘Cloud’ of hairs easily rubbed off

diagnose by history

of exposure

and pain without

inflammationfine barbed hairs in cornea, can migrate to retina

Zoonotic eye diseases

• Preferred host is non-human

• Paratenic (dead-end) visit by parasite, but damage still done!

• Two examples:

– Toxocara vitreoretinopathy

– orbital myiasis

Ocular larva migrans (Toxocara canis or cati)

• Worldwide distribution

• Risk factor: exposure to canine/feline feces

• sandbox is infective up to one year after feces deposited

Toxocara life cycle• adults in canine intestine• fecal contact by human• eggs hatch in GI tract• migrate in blood vessels• exits at end organ

–brain, eye– liver– lungs

Manifestations

• Visceral larva migrans• Ocular larva migrans

– Uveitis, hypopyon

– Macular / peripheral granuloma

– Vascular occlusive disease

• Treatment– Steroids, laser if larva alive

– Value of antihelminthics unclear

Myiasis

• Infestation of tissue or cavities by maggot (Diptera)

• Internal: subretinal migratory tracks• External: lids or conjunctiva• Orbital: debilitated patient, abscess• Treatment is excision

Dermatobia hominis

• AKA human botfly, torsalo (Central America), ‘beef worm’ (Belize), ‘mosquito worm’

• Habitat: forests and river valleys in Latin America, imported to USA

• case in Dallas County, TX, 2003• Hosts: man, cattle, dogs, birds

Dermatobia hominis• Life cycle of 3-4 months • Female attaches 15-30 eggs to a fly, mosquito, or (rarely) tick, who then transmit to egg to human host• 1mm ‘bot’ hatch, enter host at bite• grows over 6-12 weeks to 20 mm• Mature larvae exit furuncle opening, drops to ground, pupates for 14-24 days• Adult does not eat, mates within one day, and lives only one week

Larva

• Furuncular myiasis: movement often observed within opening

• Two oral hooks at distal end, two dark respiratory ‘spiracles’

near skin break

• Adult fly: ½”, yellow,

resembles a bee

Ophthalmomyiasis externa

• Treatment:

–Occlude breathing tube with beeswax, gum, ointment, fat, drop of nicotine

–Excision

–Subretinal larva: argon laser

Iatrogenic Diseases

• Rabies in corneal transplant– Most recent case - Iran, 1996– 8 reported cases (one US case in 1979)

– implications for regulation and eye banking in developed and developing world

Acanthamoeba Keratitis• Ubiquitous, warm water

• Homemade contact lens solutions and hot tubs

• Chronic pain and ulcer

• Medications (all off label use): Brolene (0.1% propamidine), PHBG 0.02% , neomycin, miconazole, others

trophozoite and cyst

clinical appearance

Signs and symptoms

• pain out of proportion to findings• paracentral ring infiltrate• prior medical failure or diagnosis of HSV

radialkeratoneuritis:infiltrate alongradial cornealnerves

Working Together• International partnerships are key!

• Address the cultural gap in research – Common understanding of disease

– Common understanding of ‘science’

The good news

• Increasing access to eye surgery• Inexpensive intraocular lenses now

available worldwide• Ivermectin and the UN’s

Onchocerciasis Control Program• Improving nutrition• Increasing opportunities for service

Summary

• Epidemiology: still much needless suffering around the world

• Synergy: culture and disease• Environment: protection is affordable• Exotics: rare but important• Iatrogenics: preventable • The future is bright

Questions?

stephen.waller@usuhs.mil