Optical coherence tomography findings in presumed veterinary anthelmintic drug-induced retinal toxicity: a glimpse into underlying mechanism

Purpose: To report optical coherence tomography (OCT) findings of presumed veterinary anthelmintic drugs (VAD)-induced retinal toxicity that may aid in understanding potential pathogenic mechanisms. Methods: This is a retrospective observational case series analysis of patients with vision abnormalities following the accidental or intentional consumption of VADs. All cases underwent a thorough ophthalmological examination. Moreover, medical records, as well as the initial and follow-up OCT images, were thoroughly scrutinized. Results: Four patients were identified (3 males; mean [range] age, 36.5 [22-52] years). Each patient overdosed on one or two of the following VADs: closantel, triclabendazole, praziquantel, pyrantel pamoate, and niclofolan. The most characteristic OCT finding was diffuse, granular, hyperreflective lesions throughout the outer retina, which were initially identified in the ellipsoid zone in two cases. At follow-up, OCT exhibited regression of hyperreflective lesions and extensive loss of the outer retinal elements in two patients. In addition, the sub-foveal outer retinal layers may be partially preserved. Conclusion: Some VADs could be detrimental to the human retina if overdosed, resulting in visual disturbances. OCT revealed the mitochondria-enriched ellipsoid zone was where outer retinal damage first appeared on, implying that these medications may harm the retina by inhibiting mitochondrial energy metabolism, as they do to eliminate parasites.