[Photocoagulation in the edematous and non-edematous retina with the cw-laser of different wavelengths]

Abstract

The impact of wavelength upon the laser power required in photocoagulation of oedematous and non-oedematous retinal areas was investigated in a restricted clinical study. The following laser systems were applied: an argon laser (514 nm), a diode-pumped frequency-doubled Nd:YAG laser (532 nm) and a diode laser (810 nm). All lasers had broadly similar properties as regards beam characteristics, beam conduction and application optics. Twenty-five eyes of 25 patients with diabetic retinopathy were included in the study. Each eye was treated with each laser in areas of edema and no edema. Apart from the wavelength, laser power was the only variable permitted. The power required for photocoagulation at 514 nm and 532 nm was identical under every aspect of the study. In comparison with 514 nm or 532 nm photocoagulations, 810 nm photocoagulations required 6.0 +/- 0.9-fold higher power settings in nonedematous retina and 5.75 +/- 1.0 fold higher power settings in edematous retina. At every wavelength investigated, retinal edema raised the average laser power needed by more than 20%. The extent of this effect seems to decline with longer wavelengths.