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Christopher Sramek, Loh-Shan Leung, Yannis M. Paulus, Daniel V. Palanker; Therapeutic Window and Lesion Character of Retinal Photocoagulation with Yellow (577 nm) and Green (532 nm) Lasers. Invest. Ophthalmol. Vis. Sci. 2011;52(14):545.
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Recently-developed compact solid state yellow lasers (577 nm) may offer an attractive alternative to traditional green (532 nm) light in retinal photocoagulation. Potential benefits include stronger absorption in oxyhemoglobin and reduced scattering in opacifications of the ocular media. In this study we compare the safe therapeutic window (TW), the ratio of threshold powers for mild coagulation and rupture of Bruch’s membrane, and histological character of retinal photocoagulation lesions with these two wavelengths in rabbit.
10 - 100 ms exposures with 200 µm aerial beam diameter at 577 and 532 nm wavelengths were applied to the retinas of 17 Dutch-Belted rabbits. Mild coagulation and rupture thresholds were determined in each eye. Change in TW with duration was analyzed using Analysis of Covariance (ANCOVA). Histology of mild coagulation lesions was acquired in 8 additional eyes to compare the lesion character.
TW was found to decrease logarithmically with decreasing pulse duration for both wavelengths. Yellow laser TW was 8 - 15% larger than green, corresponding to a difference in parallel-slope regression dTW = 0.36 ± 0.20 (P < 0.001). Histological examination of mild coagulation lesions at 1 day showed pyknotic outer nuclei, collapsed RPE cells, and mild inner retinal edema, with lesion width decreasing 39% by 1 week for both wavelengths.
Safe therapeutic window of retinal photocoagulation was improved with 577 nm wavelength over 532 nm, while histological lesion character with the two lasers was comparable. Theoretically, reduced attenuation of yellow laser in cataractous lens and opacified vitreous may improve photocoagulation in elderly patients.
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