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

Area of Science:

• Veterinary ophthalmology
• Canine neuro-ophthalmology
• Diagnostic imaging

Background:

• Chromatic pupillary light reflexes (cPLR) are used to distinguish sudden acquired retinal degeneration syndrome (SARDS) from optic pathway disease in dogs.
• This diagnostic approach aims to differentiate primary retinal dysfunction from neurological causes of acute blindness.

Observation:

• Two dogs presented with acute blindness, absent menace responses, and bilateral mydriasis.
• cPLR testing showed no response to red light but a brisk constriction to blue light.
• Electroretinograms were normal, ruling out primary retinal disease.

Findings:

• Both dogs were diagnosed with optic pathway (CNS) disease via MRI: a meningioma in one and lymphoma affecting optic nerves in the other.
• The cPLR results in these cases were inconsistent with the final neurological diagnosis.
• These are the first reported canine cases of acute blindness from optic pathway disease exhibiting a present blue light-cPLR.

Implications:

• The findings challenge the current understanding of cPLR utility in differentiating canine blindness etiologies.
• Accurate interpretation of cPLR in conjunction with other diagnostic tests is crucial for canine neuro-ophthalmology.
• Further research is needed to refine diagnostic protocols for acute blindness in dogs.