AIM: To observe the changes of MMP-9 expression in rabbit retina after laser irradiation at different thresholds of 577nm.

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.