Study of the corneal temperature variation during photo-refractive procedures

Abstract

Purpose : Refractive surgery, although it causes very few complications and a rapid recovery of the patient, very little attention has been given to the issue of corneal temperature during this type of surgical procedure. The temperature becomes something important to be evaluated because an ablation laser is used during the procedure, which can causes injuries to the tissue due to the thermal energy inserted locally in the ablation region. Thus, the idea of this study is to deepen this knowledge using a digital infrared thermal image to evaluate how invasive this procedure can be from a perspective of the thermal energy inserted in this process and its relationship with the physiology of cornea.

Methods : Thermal digital images were obtained at a distance of 40cm from the ocular surface and performed at a rate of 30 frames/s using infrared cameras, model: T540 (sensitivity <40mK/resolution 464 x 348 pixels) and A6753sc (sensitivity <30mK/640×512 pixels Flir System), the data were analyzed via software and we used infrared radiation intensity and temperature of regions of interest, ablation site, pre and post procedure eye temperature, and all areas of interest were analyzed the maximum, minimum and average temperature, and also calculated the dissipated energy in Watts. Surgery was performed in an environment with controlled temperature and humidity, ablation of the corneal surface was performed with Excimer laser, with a spherical profile of 6-7mm and maximum ablation time of 16s.

Results : Thirty uneventful surgical procedures were analyzed, with the patients acclimatized in a room at 23°C and 50% relative humidity. The average global ocular surface temperature was 30.33±0.45°C after flap-elevating in LASIK procedures or epithelial debridement in PRK procedures, before the ablation; energy input was 0.26 Watts/s exposure. The tissue returned to pre-exposure temperature 3.5s after the application of laser, on average . The peak temperature is closely linked to the laser exposure time, and the maximum peak observed was 36.11°C.

Conclusions :
In this research, in photo-refractive procedures, where peaks of almost 6 ° C on the corneal surface were observed, the 30 corneas studied were able to return to the temperature before the procedure very quickly, 3.5 seconds on average, showing a prepared physiology for these temperature variations, avoiding tissue damage. Larger diopters led to a longer recovery time.

This is a 2021 ARVO Annual Meeting abstract.