Contralateral optic neuropathy and retinopathy associated with visual and afferent pupillomotor dysfunction following enucleation in six cats

Abstract

Purpose: To investigate contralateral optic neuropathy and retinopathy following enucleation in 6 cats. Methods: Retrospective study. The medical records of cats with contralateral visual and afferent pupillomotor dysfunction following enucleation presented to the Animal Health Trust (AHT), Newmarket, UK, between January 1994 and January 2010 were reviewed. Information recorded included history, signalment, ophthalmic findings, electroretinography (ERG) (2/6) and MRI (3/6) findings and long-term outcome. Pearson's chi-square tests were used to compare breed proportions (P < 0.05). Results: Six cats aged 1.5 to 11 (median 5.5) years presented with mydriasis and/or visual deficits noted immediately following enucleation. Enucleation involved optic nerve (ON) ligation in all of the four cases for which this information was available. Ophthalmic findings included mydriasis with absent pupillary light reflex (PLR) (4/6), incomplete PLRs (2/6), absence of dazzle reflex (4/6) and absence of menace response (4/6). Funduscopy initially revealed multifocal peripapillary retinal lesions, with subsequent progressive optic nerve head (ONH) and retinal atrophy. ERG recordings revealed normal outer retinal function at 6 and 22 weeks (2/2). On MRI, the optic chiasm (OC) ipsilateral to the enucleation could not be identified and the contralateral OC was atrophied (3/3). Conclusions: The acute afferent ON deficits following enucleation, progressive ONH atrophy, normal outer retinal function and MRI demonstrating OC pathology are consistent with chiasmal injury due to traction on the ON during enucleation. Rostral traction on the globe to facilitate ON ligation is contraindicated in cats.