Optic Nerve Aplasia in a Cat: Neuro-ophthalmologic Examination and Imaging Findings

Optic nerve aplasia is an exceptionally rare congenital malformation characterized by the complete absence of the optic nerve, optic disc, retinal ganglion cells, and retinal vasculature, resulting in irreversible blindness from birth. Although well documented in human ophthalmology and sporadically reported in dogs and other species, feline cases remain exceedingly rare, limiting clinical awareness and diagnostic experience. The present report describes a unilateral case of optic nerve aplasia in a young cat, with emphasis on the integration of neuro-ophthalmologic examination and multimodal imaging. Marked anisocoria and complete absence of the pupillary light reflex, dazzle reflex, and menace response in the affected eye indicated severe afferent visual pathway dysfunction. Funduscopic evaluation was precluded by a concurrent congenital lens abnormality, necessitating reliance on advanced diagnostic imaging. Ocular ultrasonography revealed posterior segment maldevelopment and absence of the optic nerve shadow, while magnetic resonance imaging definitively demonstrated complete unilateral absence of the optic nerve from the optic chiasm to the orbital cavity, with normal contralateral optic nerve and intracranial structures. By correlating clinical findings with imaging features and existing human and veterinary literature, this case highlights the critical diagnostic role of MRI in suspected congenital optic nerve anomalies and expands the limited body of knowledge on feline optic nerve aplasia.