方法：将色素兔26只采用抽签法随机分为正常对照组2只、常规光凝组6只和阈下微脉冲光凝组18只。正常对照组不做任何处理，常规光凝组行577nm激光光凝，阈下微脉冲光凝组又亚分为三个亚组，分别行9%、12%、15%工作负载率的577nm阈下微脉冲激光光凝。采用免疫组织化学法检测各组兔眼视网膜上MMP-9的表达情况。

结果：常规光凝组：RPE层及视细胞层MMP-9呈强阳性表达，较阈下微脉冲组明显增多，差异有统计学意义(P<0.05)； 阈下微脉冲组：9%工作负载率见RPE层及视细胞层MMP-9少许阳性表达，12%工作负载率见RPE层及视细胞层阳性表达增多、胞核也出现少许阳性表达，15%工作负载率RPE层及视细胞层中度阳性表达，三个亚组间差异无统计学意义(P>0.05)。

结论：577nm阈下微脉冲光凝在9%、12%、15%工作负载率下对视网膜色素上皮层具有高度选择性，对视网膜神经纤维层无明显损伤，较常规577nm激光光凝更加安全。

METHODS: Twenty-six pigmentation rabbits were randomly divided into normal control group(n=2), conventional photocoagulation group(n=6)and subliminal micropulse laser photocoagulation group(n=18). The conventional photocoagulation group was treated with 577nm laser photocoagulation, subcutaneous micro-pulsed laser photocoagulation at a working loading rate of 9%, 12% and 15%, respectively. Eighteen rabbits were again divided into three subgroups according different powers of subthreshold working loading rate of 9%(n=6), 12%(n=6)and 15%(n=6)that undertook, respectively. The expression of MMP-9 on the retina of rabbit eyes was detected by immunohistochemistry.

RESULTS: In the conventional photocoagulation group, the expression of MMP-9 in the RPE layer and the visual cell layer was strongly positive, which was significantly higher than that in the sub-micro pulse group(P<0.05). Less MMP-9 positive expression of RPE layer and visual cell layer in the working loading rate of 9% subgroup, and more MMP-9 positive expression of RPE layer and visual cell layer in the working loading rate of 12% subgroup; little expression was also noted in the nucleus of RPE and visual cell layer. Moderate MMP-9 positive expression of RPE layer and visual cell layer was observed in the working loading rate of 15% subgroup. There were no significant differences between the three subgroups(P>0.05).

CONCLUSION: The 577nm subliminal micro-pulsed photocoagulation has high selectivity to retinal pigment epithelium at working load rate of 9%, 12% and 15%, and no damage to retinal nerve fiber layer, which is safer than conventional 577nm laser photocoagulation.