This study examined the role of oxidative stress and the effect of a single dose treatment with N-Acetylcysteine (NAC) on the temporal development of acute laser-induced retinal injury. We used the snake eye/Scanning Laser Ophthalmoscope (SLO) model, an in vivo, non-invasive ocular imaging technique, which has the ability to image cellular retinal detail and allows for studying morphological changes of retinal injury over time. For this study 12 corn-snakes (Elaphe g. guttata) received 5 laser exposures per eye, followed by either a single dose of the antioxidant NAC (150mg/kg, IP in sterile saline) or placebo. Laser exposures were made with a Nd: VO4 DPSS, 532nm laser, coaxially aligned to the SLO. Shuttered pulses were 20msec x 50 mW; 1mJ each. Retinal images were taken using a Rodenstock cSLO and were digitally recorded at 1, 6, 24-hrs, and at 3-wks post-exposure. Lesions were assessed by two raters blind to the conditions of the study yielding measures of damaged area and counts of missing or damaged photoreceptors. Treated eyes showed a significant beneficial effect overall, and these results suggest that oxidative stress plays a role in laser-induced retinal injury. The use of NAC or a similar antioxidant shows promise as a therapeutic tool.
Currently there are no universally accepted functional diagnostics and treatments for laser eye injury. The multifocal electroretinogram (MERG) determines the function of several areas of the retina simultaneously. The objective of this research is to determine if the MERG is sensitive enough to provide a functional assessment of retinal laser lesions that correlates to established contrast sensitivity/visual acuity tests currently in use. The Visual-Evoked Response Imaging System (VERIS) ClinicTM, a MERG system with continuous visualization of the fundus, was used to record from normal rhesus monkeys. The MERG mapping of the rhesus monkeys was localized to the macula and centered on the foveal region. The recordings yielded three waveforms for each of the 103-recorded responses. A difference was seen in all of the waveform mean amplitudes with the human normal values being one and one-half times as large for the first, twice as large for the second and four times as large for the third waveform. This may be due to a much lower number of subjects for recording (5 Rhesus versus 48 human recordings) or the monkey retina may, in fact, produce lower amplitude retinal responses. This on-going project is expanding research to include the functional assessment of laser retinal injury through the use of the MERG with the intent of correlating the function to currently used behavioral metrics of the visual system.