Shorter pulses used in pattern scanning photocoagulation (10-20 milliseconds [ms]) tend to produce lighter and smaller lesions than the Early Treatment Diabetic Retinopathy Study standard 100-ms exposures. Smaller lesions result in fewer complications but may potentially reduce clinical efficacy. It is worthwhile to reevaluate existing standards for the number and size of lesions needed.
The width of the coagulated zone in patients undergoing retinal photocoagulation was measured using optical coherence tomography. Lesions of “moderate,” “light,” and “barely visible” clinical grades were compared for 100, 200, and 400 μm spot sizes and pulse durations of 20 ms and 100 ms.
To maintain the same total area as in 1,000 standard burns (100 ms, moderate) with a 400-μm beam, a larger number of 20-ms lesions are required: 1,464, 1,979, and 3,520 for moderate, light, and barely visible grades, respectively. Because of stronger relative effect of heat diffusion with a smaller beam, with 200 μm this ratio increases: 1,932, 2,783, and 5,017 lesions of 20 ms with moderate, light, and barely visible grades correspond to the area of 1,000 standard burns.
A simple formula is derived for calculation of the required spot spacing in the laser pattern for panretinal photocoagulation with various laser parameters to maintain the same total coagulated area.
Shorter pulses in PASCAL photocoagulation tend to produce lighter and smaller lesions, which may result in undertreatment. Based on optical coherence tomography measurements of retinal burns, this study establishes an appropriate number of spots to coagulate the same total area. Formula is derived to calculate the spot spacing for various treatment parameters.
From the *Department of Ophthalmology and †Hansen Experimental Physics Laboratory, Stanford University, Stanford, California; ‡Department of Ophthalmology, Federal University of Sao Paulo, Sao Paulo, Brazil; and §OptiMedica Corporation, Santa Clara, California.
Funding was provided in part by the Alcon Research Institute, the Horngren and Miller Family Foundations, and the Angelos and Penelope Dellaporta Research Fund.
G. Marcellino is an employee of OptiMedica Corporation. D. Palanker and M. Blumenkranz hold a Stanford University patent on patterned scanning laser photocoagulation licensed to OptiMedica Corporation, with an associated equity and royalty interest.
Reprint requests: Daniel Palanker, PhD, Stanford University, Hansen Experimental Physics Laboratory, 452 Lomita Mall, Stanford, CA 94305-4085; e-mail: email@example.com