Corneal "Plaque" formation after anti-acanthamoeba therapy in acanthamoeba keratitis.

A 48-year-old woman presented to us with left eye microbial keratitis. Corneal scraping revealed acanthamoeba cysts on microbiology examination. After 4.5 months of treatment with chlorhexidine 0.02% and polyhexamethylene biguanide (PHMB) 0.02% eye drops she presented with a tough “plaque” lesion involving the inferior cornea. The plaque was carefully excised in toto and sent for laboratory tests. Both microbiology and histopathology examinations revealed presence of numerous acanthamoeba cysts within the plaque along with dystrophic calcification [Fig. 1].

Figure 1

(a) Slit lamp photograph demonstrating a double ring infiltrate of acanthamoeba keratitis at presentation. (b) “Plaque” formation following 4.5 months of anti-acanthamoeba therapy. (c and d) Numerous double-walled acanthamoeba cysts visible on microbiology and histopathology examination of the plaque lesion

Plaque lesions in acanthamoeba keratitis is an uncommon feature.[1] Topical anti-acanthamoeba medications alone are unlikely to result in a plaque formation, but its interaction with other drugs like dexamethasone can lead to its precipitation on the ocular surface.[2] When encountered they should be surgically excised as they may harbor acanthamoeba cysts that can lead to persistence or recurrence of the infection.

Plaque lesion in acanthamoeba, though rare, mandates surgical removal in order to decrease the infective load and allow better drug penetration.

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