A Model to Study Thermal Energy Delivery to the Choroid: A Comparison of Surgical Devices

PURPOSE: We measure and compare surgical devices using an ex vivo, temperature-controlled, choroidal incision model during thermal energy transfer with a high-resolution infrared camera. METHODS: Ex vivo porcine choroidal tissue specimens (n = 516) were isolated and placed on a temperature-regulated (37°C) perfusion platform. We tested the pulsed electron avalanche knife (PEAK), micropulse laser (MpL), continuous laser (CL), and bipolar cautery (BpC) at three energy settings (11 [low], 45 [medium], and 134 [high] mJ/mm). Each device was clamped to a stationary mechanical arm. Movement of tissue specimens beneath the surgical device was achieved using a stepping motor-driven x-y table. An infrared video camera measured orthogonal temperature variation in the surrounding tissue. RESULTS: Increased power resulted in greater lateral thermal spread using all modalities (P < 0.001). Mean (standard deviation) lateral thermal spread at low energy was smallest for the MpL at 0.0 (0.01) mm (P < 0.001), whereas BpC had the least collateral tissue damage at medium and high energies (0.02 [0.08] and 0.34 [0.22] mm, respectively; P < 0.001). Fluidics of the ex vivo system may limit thermal spread. The PEAK had the greatest thermal spread across all energy groups (P < 0.001), with clinically relevant variation between disposable blades. CONCLUSIONS: Our ex vivo model enabled direct comparison of threshold thermal tissue injury across four devices. MpL and BpC showed the least thermal damage. PEAK had a higher variation in energy delivery, but also has the advantage of more effective tissue cutting. TRANSLATIONAL RELEVANCE: Our ex vivo surgical device analysis provides thermal tissue injury predictions for choroidal surgery.