LABORATORY SCIENCES Effect of Pulse Duration on Size and Character of the Lesion in Retinal Photocoagulation

Objective: To systematically evaluate the effects of la-ser beam size, power, and pulse duration of 1 to 100mil-liseconds on the characteristics of ophthalmoscopically visible retinal coagulation lesions. Methods: A 532-nm Nd:YAG laser was used to irradi-ate 36 retinas inDutch Belt rabbits with retinal beam sizes of 66, 132, and 330 µm. Lesions were clinically graded 1 minute after placement, their size measured by digital imaging, and their depth assessed histologically at dif-ferent time points. Results: Retinal lesion size increased linearly with la-ser power and logarithmically with pulse duration. The width of the therapeutic window, defined by the ratio of the threshold power for producing a rupture to that of a mild coagulation, decreased with decreasing pulse du