Abstract
Purpose. To quantitatively evaluate the efficacy-safety balance of transscleral cyclophotocoagulation (TSCPC) through a mathematical modeling-based analysis of thermal tissue response in the ciliary body, and to determine the laser exposure parameters for achieving a selective coagulation effect in neovascular glaucoma (NVG).
Material and Methods. A model of heat transfer in the ciliary body was developed using the Pennes bioheat transfer equation. Continuous Wave (CW) TSCPC and MicroPulse TSCPC at 1 W and 2W for a single 2-s application and a series of 2-s applications were subjected to analysis. The following parameters were determined: maximum temperature (Tmax), time to reach 50 °C (t50), time in the temperature range 50–60 °C (t50-60), and time in the temperature range above 60 °C (t(>60)). Integral thermal indices including the Therapeutic Exposure Index (TEI), Destructive Exposure Index (DEI), and Thermal Selectivity Index (TSI), and Safety Margin were calculated.
Results. A single 2-s CW-TSCPC application at 1 W enabled achieving the coagulation temperature threshold (Tmax = 50.8 °C; t50 = 1.44 s) without a transition to the destructive temperature range (> 60 °C), whereas that at 2 W was accompanied by tissue overheating (Tmax = 61.8 °C; t50 = 0.4 s). A series of 2-s CW laser applications at 1 W enabled accumulation of the heat dose within the therapeutic window (t50–60 = 17.1 s; DEI = 0), whereas that at 2 W resulted in large t(>60) values (t(>60) = 39.7 s; DEI = 0.67). MicroPulse TSCPC did not result in reaching the coagulation threshold (Tmax ≤ 49 °C). The integral indices confirmed the optimal efficacy–safety balance for a CW-TSCPC application at 1 W.
Conclusion. The 60 °C temperature threshold determines the transition from coagulative to destructive tissue injury. Therefore, CW-TSCPC at 1 W provides an optimal efficacy-safety balance due to a selective coagulative effect, and can be considered a pathophysiologically justified strategy for optimizing TSCPC parameters in NVG.