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

Chromatic pupillometry and FD-OCT together reliably monitor progressive retinal degeneration and preserved ipRGC function in SARDS dogs.

This longitudinal study evaluated chromatic pupillary light reflexes (cPLR) and retinal layer thickness over 12 months in 15 dogs with sudden acquired retinal degeneration syndrome (SARDS) compared to nine control dogs, with histologic analysis of enucleated globes from five SARDS-affected and eight control dogs. At baseline (within one month of blindness onset), SARDS-affected dogs demonstrated significantly reduced extent and velocity of red light PLR and reduced extent with prolonged latency of white light PLR relative to controls. Notably, blue light PLR parameters and white light PLR velocity did not differ at baseline, suggesting early preservation of melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs). Over the 12-month follow-up period, white light PLR velocity declined significantly in SARDS-affected dogs. Fourier-domain optical coherence tomography (FD-OCT) revealed progressive total retinal thinning driven by outer retinal degeneration, while inner retinal thickness remained stable. Histologic examination confirmed diffuse outer retinal atrophy with relative inner retinal preservation, and ganglion cell counts did not differ between SARDS-affected and control eyes. These findings indicate that ipRGC function is selectively preserved despite progressive photoreceptor loss in SARDS. The authors conclude that combined longitudinal chromatic pupillometry and FD-OCT provides a comprehensive, non-invasive framework for monitoring both functional and structural retinal changes in SARDS-affected dogs, with chromatic pupillometry serving as a clinically useful tool for assessing ipRGC integrity over time.

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