Retinal effects of the frequency-doubled (532 nm) YAG laser: histopathological comparison with argon laser

Retinal lesions produced in Dutch Cross rabbits with a frequency-doubled (532 nm) YAG laser in single pulse mode (30-100 microJ) and in train of uniform pulses (2.6 and 7.5 mJ) underwent histopathological examination by light and electron microscopy. The results were compared to argon laser lesions (11 and 15 mJ) in the same animals. Low-energy single-pulse YAG lesions produced separation of the neural retina from the retinal pigmented epithelium (RPE), while higher energies caused severe disruption of retinal structures with moderate damage to the RPE. A striking and consistent finding of all the single-pulse lesions was the presence of red blood cells between the RPE and neural layers. The findings appear to support a process of mechanical disruption. In contrast, the lesions produced by a uniform train of pulses showed well-defined damage to RPE and photoreceptors with no red blood cells between these two layers, no choroidal damage, and relatively little disruption of the inner retina. The typical argon lesion evidenced cellular damage from the RPE through all retinal layers. Leukocytes in the choroid contained "holes" or vacuoles not seen in YAG lesions. Both the uniformly pulsed YAG laser burst and argon laser produced effects consistent with a thermal process. Some differences between argon and YAG burst were observed. The results suggest that there may be a clinical potential for the 532-nm burst YAG in treating retinopathies.