Abstract
Purpose :
Ocular hypothermia can be therapeutic during periods of acute retinal ischemia, or to induce a protective effect against future ischemia (hypothermic preconditioning). Current methods to cool the ocular tissues are not regulated (e.g. cold packs) or difficult implement (e.g. perfusion of cooled saline on the eye surface). Here we demonstrate targeted cooling of the eye using a regulated, wearable thermoelectric device.
Methods :
The Eye Cooler System (ECS) is comprised of a contoured eye contact ring held in place by the eyelids, a thermoelectric heat pump, and an active convection heat sink. A 14 mm diameter area centered over the cornea is unobstructed during use. An integral temperature sensor at the eye surface provides feedback. Fresh pig eyes (n = 5) were imaged using MRI to document gross anatomy, then instrumented with temperature sensors at five key locations. The ECS was positioned to contact the sclera, and the eye was then lowered to the level of the ECS contact ring (approximately 4 mm peripheral to the limbus) into a 37 C oil bath and the eye allowed to reach equilibrium at typical physiological temperature (34.5 C). The ECS was turned on and the temperatures monitored as a function of time. The ECS sensor / feedback ensured the sclera was never below 3.7 C. After 20 minutes of ECS cooling, the eye was removed from the system and imaged using micro-CT to document the precise location of each implanted temperature sensor.
Results :
On average, the temperature at the ECS sensor, located adjacent to the sclera, reached 4 C within three minutes of turning the system on. Final equilibrium temperatures, and the times to reach 90% of the final change in temperature at each sensor location (mean across 5 eyes), were: anterior sclera, 10.7 C, 194 sec; equatorial sclera, 25.0 C, 338 sec; posterior sclera, 24.4 C, 532 sec; vitreous, 22.4 C, 569 sec; proximal optic nerve, 30.2 C, 703 sec. Temperature vs time profiles were similar across eyes, with root mean squared differences from the mean profile of 11 - 29%, depending on sensor location.
Conclusions :
In the non-perfused eye model, the ECS was able to achieve therapeutically relevant temperatures throughout the eye, including the proximal optic nerve. Equilibrium temperatures could be maintained for as long as the system was powered. Next steps include measuring ECS-induced temperature changes in a perfused eye model.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.