In Vivo Measurement of Long-Term Laser Induced Retinal Temperature Rise

Threshold temperatures corresponding to the formation of both ophthalmoscopically and microscopically visible lesions were measured in 10 rhesus monkey eyes using 9, 100, and 1000 s exposures from a CW krypton laser (647.1 nm). Measurements were compared to a thermal model of retinal injury. Average threshold temperatures at 9, 100, and 1000 s in the macula were 17, 14, and 120C, respectively. Measured temperatures at the image center at 9 s were generally one-third as large as predicted temperatures. Measurements of 9 s threshold temperatures agreed with the 10 s threshold temperature data of Welch et al. [11] within 4 percent in the macula and 22 percent in the paramacula. Using rate-process damage coefficients derived from measured threshold temperatures, threshold energy densities at the cornea were predicted with a thermal model and they were within 13 percent of data from the literature. In comparison, the power required for damage from 120 s exposure to blue light produced a measured temperature rise of only 0.7°C, well below the expected lower limit of temperature required for thermal damage.