Comparison of longitudinal changes in chromatic pupillometry in normal dogs and dogs with sudden acquired retinal degeneration syndrome

Abstract

Purpose : To determine chromatic pupillary light reflex (PLR) parameters in dogs with and without sudden acquired retinal degeneration syndrome (SARDS) over time.

Methods : Five dogs with acute vision loss within the previous 6 months, a normal fundus, and a flat-line electroretinogram (ERG) were diagnosed with SARDS; 5 age-matched sighted dogs with a normal fundus and ERG served as controls. Both groups underwent red (630nm), blue (480nm), and white light stimulation using a chromatic light source (Melan-100^®) adapted for video pupillometry. The tests were repeated for the SARDS-affected dogs at 6 months (6m) and 1 year (1y) post-diagnosis. Pupil size was estimated using ImageJ software, and degree, latency, and velocity of pupil constriction were calculated.

Results : SARDS-affected dogs had significantly reduced (P<0.001) pupil constriction in response to red (8.6±7.1% at 6m and 5.7±6.3% at 1y) and white (37.2±21.3% at 6m and 32.1±7.5% at 1y) light vs. control dogs [red: 70.9±14.5% (P<0.001); white: 62.7±11.7%], but no difference in response to blue light (77.1±6.8% at 6m and 77.3±9.3% at 1y of SARDS-affected dogs vs. 88.5±5.0% of control dogs; P=0.666). Pupil constriction latency in response to red (5.8±4.9s at 6m and 9.1±2.2s at 1y) and white light (0.7±0.4s at 6m and 3.2±3.7s at 1y) was significantly longer in SARDS-affected dogs compared to controls [red: 0.5±0.1s, P<0.001 and white: 0.4±0.1s, P=0.17], but both groups responded similarly to blue light. SARDS-affected dogs >1 year from diagnosis responded more slowly to white light than did controls or those SARDS-affected dogs within 6 months of diagnosis. Velocity of pupil constriction did not significantly differ between affected dogs and controls for blue (P=0.946), or white (P=0.292) light at any of the time points tested. Velocity of pupil constriction in response to red light (0.00016±0.0002mm/ms) was significantly slower in SARDS-affected dogs at 6-month post-diagnosis compared to age-matched controls (0.0013±0.0005mm/ms; P=0.006).

Conclusions : The Melan-100^® can be adapted for video capture pupillometry in unsedated dogs. When compared to normal age-matched control dogs, SARDS-affected dogs demonstrated a decreased degree and prolonged latency of pupil constriction in response to both red and white light, and these differences became more pronounced with increased time from diagnosis.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.