Infrared pupillometry to measure pupil light reflex in awake cats: Feasibility and evaluation pre- and post-opioid...

Assessing pupil diameter and pupillary light reflexes (PLR) in a clinical setting can be challenging due to the pupil's sensitivity to light and the rapid nature of these reflexes. Pupillometry is a technique that is helpful in human medicine in anesthesiology and critical care medicine. However, evidence in veterinary medicine is scarce on the application of pupillometry and analgesic response. Therefore, the aim of this pilot observational study was to assess the feasibility and reliability of portable pupillometry in cats, identify individual factors influencing pupillometric parameters, and compare measurements before and after analgesic administration. Twenty-eight cats, including healthy and hospitalized sick cats, underwent pupillometry using a Neurolight® device. Pupil diameter, PLR parameters, and 4 A-VET pain score were measured before and after opioid administration. Test-retest reliability was evaluated, and the influence of factors was analyzed using multivariate models. Pupillometry was feasible in 97 % of cats, with measurements being easier in hospitalized sick cats. Good reliability was observed for pupil diameter measurements, while PLR parameters showed poor reliability. Weight was significantly associated with pupil size, potentially due to the relationship between body weight and eyeball size. No association was found between pain scores and pupil diameter, and no significant changes in pupil size were observed after opioid administration. In conclusion, portable pupillometry using the Neurolight® is feasible in cats and provides reliable pupil diameter measurements. However, the device is not suitable for objective PLR assessment in this species. Further studies are needed to better understand the factors influencing pupillometry measurements in cats.