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Pet spiders and the eye

Arachnid house pets drive apparent rise in ophthalmia nodosa incidence

Howard Larkin

Posted: Sunday, April 1, 2018

The previously healthy 17-year-old male presented after two weeks of intense foreign body sensation, photophobia and periocular rash that had spontaneously resolved. Though his visual acuity was 20/20, IOP normal and skin on the lids appeared normal, his conjunctiva was diffusely injected, and he had nummular stromal opacities scattered about the cornea, associated with 2+ cell and flare of the anterior chamber.

At the slit lamp, discrete corneal lesions were observed. Some were superficial, others very deep, and each lesion was associated with a small, linear refractile structure. One of these structures perforated the posterior cornea and was associated with keratic precipitate on the endothelium, Mark J Mannis MD told the American Academy of Ophthalmology 2017 Annual Meeting in New Orleans, USA.

Having seen similar cases, Dr Mannis suspected ophthalmia nodosa. First described by Saemich in 1904, it is caused by setae – fine, sharp spines or hairs – launched by some caterpillars and spiders to discourage potential predators. The spines measure from 0.06mm to 1.5mm, are coated with irritating proteins and have microscopic barbs that prevent them from backing out once they are embedded in tissues. In the eye, rubbing and movement of the globe propel the spines deeper, potentially into the anterior chamber, iris, lens, vitreous or even the retina.

So Dr Mannis asked some pointed questions – and the patient revealed he had a pet tarantula. “Interestingly, his name was Blade,” Dr Mannis said.

GROWING THREAT
Tarantulas are an increasingly common household pet, said Dr Mannis, of the University of California – Davis Eye Center, Sacramento, California, USA. Many varieties, particular non-venomous species as large as 30cm in diameter from Mexico and Brazil, defend themselves by rubbing their legs across their dorsal abdomen, spraying clouds of barbed hairs into the air. As a result, ophthalmia nodosa is increasingly seen.

Ophthalmic manifestations include conjunctivitis, localised or diffuse keratitis, iridocyclitis and even chorioretinitis and endophthalmitis. Natural history generally progresses from initial reaction to a quiescent interval, followed by resolution or advancing to iritis and keratoconjunctivitis, with periodic recurrences, Dr Mannis said (Watson PG, Sevel D. BJO 1966; 50:209-217).

Treatment consists of observation and topical corticosteroids, Dr Mannis said. Outcomes are variable, ranging from spontaneous resolution leaving behind small corneal scars, to chronic iritis, granuloma formation or even phthisis bulbi.

“My advice to the clinician is, take a careful history and know what your patient is exposed to. My advice to the patient is – get a dog,” Dr Mannis concluded.

Mark J Mannis: mjmannis@ucdavis.edu


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