The impact of spot size, spacing, pattern, duration and intensity of burns on the photocoagulation index in a geometric simulation of pan-retinal laser photocoagulation

Purpose To evaluate the impact of spot size, spacing, pattern, duration and intensity of burns on the photocoagulation index, using a geometric simulation of pan-retinal laser photocoagulation. Methods Simulations of full-scattered pan-retinal laser photocoagulation were performed on a retinal map, using a geometry-based method. Simulations consisted of 300-, 400- or 500-μm diameter equidistant spots on the retina with 1.0-spot width spacing, as well as 400-μm diameter spots on the retina in an equidistant pattern or grid pattern, with 1.0-, 0.75-, 0.50-, 0.25- or 0-spot width spacing. For each simulation, we calculated the ratio of the total photocoagulated retinal area to the whole retina, termed the photocoagulation index. We recalculated the photocoagulation indexes using the expansion ratios of photocoagulated lesions by different duration and intensity of burns from a previous study. Results The photocoagulation indexes of the simulated pan-retinal laser photocoagulation with 300-, 400- and 500-μm diameter spots were 20.8%, 20.6% and 21.0%, respectively. The photocoagulation indexes of the 1.0-, 0.75-, 0.50-, 0.25- and 0-spot width spacing configurations of pan-retinal laser photocoagulation burns for the equidistant pattern were 20.6%, 27.1%, 36.7%, 53.2% and 83.1%, respectively, and those for the grid pattern were 17.9%, 23.5%, 31.8%, 46.1% and 72.0%, respectively. The photocoagulation indexes obtained with the equidistant and grid patterns changed (range, 1.7-84.7% and 1.5-73.4%, respectively) when the duration or burn intensity of the pan-retinal photocoagulation was changed. Conclusion This geometric simulation method could evaluate the impact of a range of conditions on the photocoagulation index.