Ivermectin-induced blindness in a Jack Russell terrier dog: Diagnosis and monitoring with electroretinography and chromatic pupillary light reflexes

A 4-year-old, neutered, female Jack Russell terrier presented with acute blindness, tremors, ataxia and rotatory nystagmus. Ophthalmic examination revealed absent menace response, dazzle reflex and pupillary light reflex, along with vermiform retinal lesions bilaterally. Electroretinography and chromatic pupillary light reflex testing showed markedly attenuated outer retinal responses. Despite no known exposure, ivermectin toxicosis was suspected based on clinical and fundoscopic findings. The dog was treated with two intravenous lipid emulsion therapies, corticosteroids and supportive therapy. Vision returned 6 days after presentation. Follow-up revealed improved electroretinography and chromatic pupillary light reflex responses, with residual retinal scarring. Toxicology confirmed serum ivermectin concentration at 1300 ppb. This case illustrates that ivermectin toxicosis can occur in MDR1-negative dogs and should be considered in cases with acute blindness, even without a known exposure history.