Chromatic Pupillary Light Reflex in Two Dogs With Amaurosis Secondary to Optic Pathway Disorders

Abstract

Objective: Chromatic (colorimetric) pupillary light reflexes (cPLR) are reportedly useful in canine neuro-ophthalmology to differentiate sudden acquired retinal degeneration syndrome (SARDS) from optic pathway disease (neurological disorders) causing acute blindness. We report two canine cases with cPLR test results reported to be consistent with primary retinal disease that were subsequently diagnosed with optic pathway (CNS) disease. Animals studied: A 7-year-old Dachshund and a 7-year-old Weimaraner were presented for acute blindness. Procedures and results: Both dogs failed obstacle tests, showed absent menace responses, bilateral mydriasis, and absent PLRs with white light in both eyes. The cPLRs were tested using a BPI-50 Precision Illuminator (Retinographics Inc., USA). Both dogs exhibited no PLR with red light (660 nm), and brisk though incomplete pupillary constriction with blue light (465 nm) at 200 kcd/m2. Electroretinograms (ERG) of both eyes were normal in both dogs. Magnetic resonance imaging (MRI) of the brain revealed a left-sided cystic extra-axial mass (suspected meningioma) in the rostral cranial fossa in the Dachshund and a lesion affecting the rostral bones of the skull base and optic nerves in the Weimaraner (confirmed lymphoma). Conclusions: These are the first two reported canine cases with acute, bilateral amaurosis due to optic pathway disease with present blue light-cPLR.