Microfilaria in the cornea in onchocerciasis

148 TRANSACT~NS

OF THE

ROYALSOCEIYOFTROPKAL MEDICINE ANDHYGIENF.

Microfilaria

in the cornea

(1987) 81, 148

in onchocerciasis

HUGH R. TAYLOR AND TERRY GEORGE Ocular Onchocerciasis Research Unit, International Center fm Epidemiologic and Preventive Ophthalmology, The Wilmer Institute, The Johns Hopkins Hospital, Baltimore, MD 21205, USA

The contact wide-field specular microscope opens a whole new field of study of changes in the corneal stroma as well as enabling the corneal endothelium to be photographed. We have recently had the opportunity to study in detail a white male who became infected with onchocerciasis while working in an endemic area of West Africa. He had numerous microflariae in a standard skin snip examination (TAYLOR, 1984), although a palpable nodule was not present. Ocular examination showed normal visual acuity; but on slit-lamp examination, numerous microfilariae were seen in the anterior chamber and the cornea of each eye and an intraretinal microiilaria (MURPHY et al., 1984) was found in one eye. Microfllariae in the anterior chamber were best seen after he had been positioned with his head between his knees for at least two minutes. This allowed the microfilariae in the anterior chamber to collect in the centre of the cornea. In the cornea, live microiilariae can be much more dif8cult to visualize because they are far less motile and are almost transparent. They are best seen with high magnification using retroillumination produced by an oblique beam reflected from the iris. Dead microfilariae, however, are more readily seen, being opaque, and can be visualized by direct illumination. Microfllariae are most common in the peripheral cornea, especially temporally and nasally. Dead microfihtriae are frequently surrounded by an infhunmatory infiltrate that appears as an ill-defined punctate fluffy or snowflake opacity about 05 mm in diameter (Fig. 1). Histologically, these opacities are focal collections of lymphocytes and eosinophils with local oedema (GARNER, 1976). Punctate keratitis sometimes occurs in patients who have not received treatment, but it is more commonly seen in people receiving microfilaricidal treatment such as diethylcarbamazine, when many microfilaria are killed synchronously (TAYLOR & GREENE,1981). With time, the micro6laria disintegrates and disappears, and finally, the punctate opacity disappears without leaving any visible sign of structural damage. Although the opacities may form within a few hours of $ethhKbamazme therapy, they take 1 to 2 months In the ‘patient we examined, we were able to perform specular microscopy of a punctate opacity (Fia. 2) that clearlv shows the straiahtened. nartiallv d&teRrated micr&laria surroundid by &unmatory infiltrate in the stroma. We are not aware of any previous examples of specular microscope photographs of microfilaria. It may well be that specular microscopy will provide a useful method for documenting and following the evolution of punctate opacities in onchocerciasis.

Fig. 2. The samemicrolilaris seenon specular microscopy. The ends of the micro6laria are indicated by arrows. References

Murphy, R. P., Taylor, H. R. & Greene,B. M. (1984).

Chorloretinal damage in onchocerciasis. American Journal of Ophthalmology, 98, 519-521. Taylor, H. R. (1984). Onchocerciasis. In: Duane, T. D. (editor). Clinical Opthalmology, Vol. 5, chapter 62. Hagerstown: Harper and Row. Taylor, H. R. & Greene, B. M. (1981). Ocular changes with oral and transepidermal diethylcarbarnazine therapy of onchocerciasis. British 3ournal of Ophthalmology, 65, 494-502. Accepted for publication

15th May,

1986.