Retinal damage profiles and neuronal effects of laser treatment: comparison of a conventional photocoagulator and a novel 3-nanosecond pulse laser

Abstract

PURPOSE: To determine detailed effects to retinal cells and, in particular, neurons following laser photocoagulation using a conventional 532 nm Nd:YAG continuous wave (CW) laser. Furthermore, to determine whether a novel 3 ns pulse laser (retinal regeneration therapy; 2RT) could specifically ablate retinal pigment epithelium (RPE) cells without causing collateral damage to other retinal cells. METHODS: Adult Dark Agouti (DA) rats were separated into four groups: control, CW laser (12.7 J/cm2/pulse, 100 ms pulse duration), or 3 ns pulse 2RT laser at one of two energy settings (“High,” 2RT-H, 163 mJ/cm2/pulse; “Low,” 2RT-L, 109 mJ/cm2/pulse). Animals were treated and killed after 6 hours to 7 days, and retina/RPE was analyzed by histologic assessment, Western blot, polymerase chain reaction, and immunohistochemistry. RESULTS: Both lasers caused focal loss of RPE cells with no destruction of Bruch's membrane; RPE cells were present at lesion sites again within 7 days of treatments. CW and 2RT-H treatments caused extensive and moderate damage, respectively, to the outer retina. There were no obvious effects to horizontal, amacrine, or ganglion cells, as defined by immunolabeling, but an activation of PKCα within bipolar cells was noted. There was little discernible damage to any cells other than the RPE with the 2RT-L treatment. CONCLUSIONS: Conventional laser photocoagulation caused death of RPE cells with associated widespread damage to the outer retina but little influence on the inner retina. The novel 3 ns 2RT laser, however, was able to selectively kill RPE cells without causing collateral damage to photoreceptors. Potential benefits of this laser for clinical treatment of diabetic macular edema are discussed.