Preliminary Investigation Of The Mechanism Of Retinal Photo Injury

Objective: to investigate the relationship between retinal photo injury and optic cell apoptosis so as to study the generation and development mechanism of retinal photo injury.Methods: Forty-five mice were divided randomly into control and experimental groups. All mice were maintained under cyclic light environment for 7 days, and then kept in darkness for 36 hours before the experiment .The experimental groups were exposed to intensive cool fluorescent light for 2 hours and then killed at the following time points after light exposure ,0hr,4hr,8hr,16hr,24hr, 36hr,48hr and 72hr,with the latter time intervals after exposure spent in darkness. Retina samples were stained by HE and TUNEL (TDT-mediated dUTP nick end labelling) method. The pathological changes of the retina were examined with light and transmission electronic microscopy. The thickness of the out nuclear layers and apoptosis index were measured with Photo Analysis System.Results: Before light exposure the retina was morphologically normal with distinct structural layers and regular arrangement of outer and inner segment. No positive marked cell was found whenwe distinguished apoptotic cells by TUNEL method. Nuclear chromation had even electronic density. After light exposure the arrangement of outer and inner segment was disordered. The inner segment and the outer segment were swollen and disorganized. The thickness of the out nuclear layers decreased. TUNEL-positive nuclei were observed only in the outer nuclear layer beginning on 4hr. The nuclear chromation gathered under the nuclear membrane, showing a typical symbol of apoptotic cells with a circled nucleus. The photo injury in retina became worse and worse and the number of apoptosis optic cells became more and more with the time increasing after light exposure. The peak occurred at 24hr and then only a few TUNEL-positive nuclei were observed after 72hr. The thickness of the out nuclear layers and apoptosis index have correlation relationship. The outer segment was disorganized. The mitochondria of the inner segment were swollen and spherical change. The nuclear membrane shrinked .The condensation and margination of the chromatin were found in the nuclear layer. All the retina samples were observed without inflammatory response under light and electron microscope.Conclusion: Apoptosis is an important mechanism in light-induced retinal damage. It is the light-induced damage that triggers the apoptosis of photoreceptor cells. Photo injury and optic cell apoptosis had impartible relationship.