Histopathology of the Effects of Tuneable Dye Laser on Monkey Retina

The tuneable dye laser was used to simulate treatment of choroidal neovascularization and panretinal photocoagulation (PRP) in monkey retina. The histopathologic effects of wavelengths from 560 to 630 nm in juxtafoveal, papillomacular bundle, and nonfoveal areas were investigated. An unexpected observation using high-intensity burns in juxtafoveal and, to a lesser extent, in papillomacular bundle areas was inner retinal damage with 600-nm light. At moderate energy levels, the effects of 600 nm were more comparable with those with other wavelengths and included much less damage to the inner retinal layers. At mild energy levels, the effects were comparable with other wavelengths. During and after the application of the burns, the energy levels and ophthalmoscopic appearances were comparable for each wavelength for the high-, moderate-, and mild-intensity burns. The histopathologic effects of 630-nm light (tuneable dye red) were comparable with those of the standard krypton red (647 nm) laser. Nonmacular and PRP effects were similar with all wavelengths. These results indicate that power levels may need to be reduced when placing 600-nm (orange) laser burns in the macula.