Ultrastructural Analysis of Rabbit Retina Irradiated with a New 670-nm Diode Red Laser at Different Powers

Purpose: Diode lasers have compact dimensions, efficient electric-optical conversion, absence of major cooling requirements, long useful life, and minimal maintenance. We verified the structural and ultrastructural effects of diode red laser emissions at 670 nm on pigmented rabbit retina. Methods: Transpupillary laser pulses were applied to rabbit retinas at variable powers with a spot size of 500 mu m (approximate to 1,000 mu m at the retina level) and duration of 200 milliseconds. Light and electron microscopic analyses were performed. Results: Subthreshold nonvisible lesions were produced using a power of 200 mW. Ophthalmoscopically visible lesions were produced using a power of 400 mW. More prominent lesions were obtained using a higher power (600 mW). Structural and peculiar ultrastructural changes correlated with the power used. In general, damage was incurred by the retinal pigment epithelium with extension into the superficial choroid posteriorly and into the outer retina anteriorly. The inner retina was involved at higher power levels. Conclusions: Ultrastructural analysis of rabbit retina treated with the 670-nm diode laser adds newer insights on tissue changes after thermal irradiation. The effects observed are consistent with those reported for the krypton red laser. The 670-nm diode laser is an economic small-size photocoagulator that appears to be a promising modality for transpupillary laser photocoagulation of the retina.