Retinal OCT Parameters and Physiological Dynamics as an Effect of Anesthesia in C57BL/6J Mice

Anesthetics are commonly used to immobilize mice for ophthalmic research, however, by using anesthetics, the physiology of the mice is temporarily changed. In this work, optical coherence tomography (OCT) parameters and physiological dynamics under anesthesia are investigated for both sexes.

Adult C57BL/6J mice (10 male and 10 female) were investigated in three groups. Group I was first injected with a mixture of medetomidine, midazolam, fentanyl, and ketamine (MMFK) and, after 1 week, were exposed to isoflurane and yet another week later injected with ketamine-xylazine (KX), whereas for the other groups the order of the anesthetics was permutated. Retinal OCT volumes were acquired every 5 minutes for a duration of up to a total of 60 minutes. Simultaneously, heart rate (HR), mean blood pressure (BP), and body temperature were recorded. Retinal thickness and pulsatile motions within the retina were quantitatively assessed in the OCT data and longitudinally charted. The data were evaluated through a mixed effects model and Bland-Altman plots.

HR, BP, and pulsatile motions within the retina differed significantly for both sexes between all anesthetics. For the retinal pulsations at the inner limiting membrane (ILM) and retinal thickness (RT), statistically significant differences were observed between male and female mice. MMFK, KX, and isoflurane also differently affected blood vessel size in the superficial vascular plexus (SVP).

The choice of anesthesia impacts the physiology of mice. Moreover, the sex of the mouse needs to be considered in the design and comparison of longitudinal OCT investigations using methods such as OCT angiography (OCTA) or phase-based OCT modalities.