Transient Simulation of Multi-Spot Retinal Laser Irradiation Using a Bio-Heat Transfer Model

Abstract

Transient numerical simulation of sequential, multi-spot, retinal laser irradiation resembling an actual surgery is performed. The retinal and adjacent regions are irradiated in a truncated three-dimensional computational domain by a 3 × 3 square array formed by nine uniformly distributed laser spots, each heated with 0.2 W power. A finite volume formulation of the bio-heat transfer model is employed as the governing equation to generate the temperature evolution. Within the heating duration of each retinal spot (∼100 ms), it is essential the temperature of the previously heated adjacent regions quickly reduce well below 60°C, the photocoagulation temperature. For an adjacent spot distance of D ≥ 0.6 mm, transient heat diffusion to the adjacent region is shown to be sufficient to reduce the retinal temperatures close to 37°C. Irrespective of the distance between two consecutive spots in an array, pulsating the laser power with a frequency determined to maintain the maximum temperature within ±10% of 60°C reduces excess heating and prevents long term retinal thermal damage.