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Stephen Anthony LoBue, Prashant Tailor, Paul Loftness, Timothy W Olsen; A Model to Study Thermal Energy Delivery to the Choroid: A Comparison of Surgical Devices. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5937. doi: https://doi.org/.
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To describe an ex-vivo model to compare thermal energy delivery that is applicable to a surgical incision of the choroid. We hypothesize that thermal tissue injury will spread from a surgical device into the tissue and can be measured with a thermal camera in an ex-vivo, temperature-controlled model.
Ex-vivo porcine choroidal tissue specimens (n = 516) were isolated and flat mounts were placed on a temperature controlled perfusion platform with a consistent temperature of 37oC. Four thermal delivery devices (micropulse laser, continuous laser, bipolar cautery, and pulsed electron avalanche knife) were standardized and tested by passing each tissue specimen horizontally beneath the selected devices, which were clamped to a mechanical arm, creating three uniform power settings across the modalities: low, medium, and high (11, 45, and 134 mJ/mm, respectively). The rate for each of four devices was calculated and controlled using a stepper-motor-driven x-y table that moved each specimen at a constant rate. An infrared video camera measured the thermal tissue profile as energy extended into the surrounding tissue. We analyzed each image to determine the affected orthogonal distance from the device’s path on the tissue (in mm) using the threshold temperature of ≥ 49oC (above this temperature results in cell death).
Lateral thermal spread in the low energy group was lowest using a micropulse laser that had undetectable threshold injury compared to other modalities (p<.01). The PEAK (pulsed electron avalanche knife) had higher thermal threshold values in the low, medium, and high-energy groups (p<0.01), yet incised the tissue. We found a modest level of variation using the PEAK between each blade and detected decreasing energy delivery with consecutive use. While a bipolar cautery device had the least collateral tissue damage for medium and high-energy groups, there was an insufficient fluid interface that limited the energy into the tissue.
We developed an ex-vivo model to measure threshold thermal tissue spread from a surgical device using isolated porcine choroidal tissue specimens. The micropulse laser and bipolar cautery had the least thermal damage across all groups. PEAK had a higher variation in energy delivery, yet also has the advantage of more effective tissue cutting.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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