Longitudinal Evaluation of Chromatic Pupillometry and Retinal Thickness in Dogs With Sudden Acquired Retinal Degeneration Syndrome

OBJECTIVE: To determine longitudinal changes in chromatic pupillary light reflexes (cPLR) and retinal layers in dogs with sudden acquired retinal degeneration syndrome (SARDS). ANIMALS STUDIED: Clinical evaluation: Fifteen SARDS-affected and nine control dogs. HISTOLOGY: Achieved globes from five SARDS-affected (1-7 years post-diagnosis) and eight age-matched controls. PROCEDURES: Dogs underwent ophthalmic examination and electroretinography to confirm SARDS. Chromatic pupillometry and Fourier-domain optical coherence tomography (FD-OCT) were performed at baseline (once for control; < 1-month post-blindness for SARDS-affected dogs), and follow-up (3, 6 and 12 months post-diagnosis). The extent, velocity and latency of pupil constriction were evaluated. Retinal thickness was measured from the FD-OCT images. Ganglion cell counts were determined from histologic sections stained with hematoxylin and eosin. RESULTS: At baseline, SARDS-affected dogs showed significantly reduced extent and velocity of red light PLR, and reduced extent with prolonged latency of white light PLR, relative to controls; white light velocity and all blue light parameters did not differ. White light PLR velocity significantly decreased over time in SARDS-affected dogs. FD-OCT in SARDS-affected dogs revealed progressive total retinal thinning but stable inner retinal thickness. Histology of SARDS-affected eyes identified diffuse outer retinal atrophy with relative inner retinal preservation; ganglion cell counts were not different between groups. CONCLUSIONS: Chromatic pupillometry reflects the selective preservation of melanopsin-containing retinal ganglion cell function despite progressive photoreceptor degeneration in SARDS. The combined longitudinal use of chromatic pupillometry and FD-OCT provides a comprehensive assessment of the evolving functional and structural changes in SARDS-affected dogs.