Optic neuritis in dogs: 96 cases (1983‐2016)

Objective To characterize ocular and neurologic findings, causes, and treatment outcomes of dogs with optic neuritis. Procedure Medical records from dogs with a diagnosis of optic neuritis at North Carolina State University, College of Veterinary Medicine, Veterinary Hospital between 1983 and 2016 were reviewed. Results Ninety‐six cases (20 unilateral, 76 bilateral), comprised of 38 males and 58 females with a mean age of 6.1 ± 3.0 years (range 0.5‐13), were identified. Seventy‐four cases were presented for vision loss, and 42 had other concurrent neurologic abnormalities. Funduscopic findings included optic nerve head elevation ( n  =   92), peripapillary retinal edema or separation ( n  =   37), retinal hemorrhage or dilation of retinal vasculature ( n  =   23), and multiple inflammatory foci in the peripapillary region ( n  =   13). Retrobulbar optic neuritis was diagnosed in four cases. The final diagnoses included the following: multifocal meningoencephalitis of unknown etiology ( MUE , n  =   35), isolated optic neuritis (I‐ ON , n  =   42), neoplasia ( n  =   10), microbial infection ( n  =   6), orbital inflammation ( n  =   2), and suspected ivermectin toxicosis ( n  =   1). Dogs with I‐ ON were more commonly male, and medium‐to‐large breed, when compared to dogs with MUE . Follow‐up was available in 72 cases, 50 of which remained blind, 10 had partial visual improvement, and 12 were assessed as having normal vision in the affected eye(s). Conclusion Optic neuritis was most commonly associated with multifocal MUE or was isolated as the sole neurologic finding, with a similar incidence between the two groups. Findings suggest that a clinical syndrome of isolated optic neuritis, distinct from multifocal MUE , occurs in dogs.