Objective To investigate the role of Caspase-3 in retinal damage caused by light exposure in rats. Methods Light injury to retina was induced by persistent exposure to illumination （intensity:30000±50lux） of operating microscope for 30 minutes in the right eyes of Sprague-Dawley rats. The pathological changes of retina were observed under optical and electron microscopies at different time points

which were 6 hours

1

3

7

and 15 days after the light exposure. Apoptosis of retinal cells was analyzed by flow cytometry. The activity of Caspase-3 was evaluated by using the Caspase-3 assay kit. At the same time

the expression of Caspase-3 protease was determined with Western blot analysis. Results The examination results of optical and transmission electron microscopes showed that edema of inner and outer segments of the retina

especially the chondriosome inside the inner segment

became obvious 6 hours after the light exposure. The change was deteriorated along with the increasing time. The structures of the discoidal valve dissociated in the outer segment simultaneously. Disorderly arranged nuclei

karyopycnosis

and thinning in the outer nuclear layer were observed. The retinal pigment epithelium almost disappeared during the later stage. The staining results of Annexin-V combined with PI demonstrated that the proportion of apoptotic cells increased with time. The proportion between 7th day （82.7%） and 15th day （80.4%）

however

showed no significant difference. Caspase-3 became remarkably active with the lapse of time

which increased from 0.02 at 6th hour to the peak of 9.8 at 7th day before it started to descend. The Western blot detected a expression of the active form of Caspase-3 at 7th day and 15th day.Conclusion Apoptosis of photoreceptor cells is markedly involved in the light damage and Caspase-3 protease may play an important role in the apoptotic process of the retina after light exposure in rats.