In vivo imaging and quantitative evaluation of the rat retinal nerve fiber layer using scanning laser ophthalmoscopy

PURPOSE. To determine whether scanning laser ophthalmoscopy (SLO) is useful for in vivo imaging and quantitative evaluation of rat retinal nerve fiber layer (RNFL) using an optic nerve crush model. METHODS. The optic nerve of the right eye was crushed intraorbitally with a clip. The left eye served as the untreated control. Fundus images of both eyes were recorded by SLO using an argon blue laser before and 1, 2, and 4 weeks after optic nerve crush. The focused plane was sequentially moved by changing the refractive values in the SLO setting. The range of refractive values (Delta F) in which the RNFL reflex was clearly observed was determined. The RNFL thickness in retinal sections was measured and compared to the Delta F value from SLO images taken before histologic preparation. RESULTS. Striations of RNFL radiating from the optic disc were clearly visible by SLO. No obvious changes in the RNFL reflex were observed 1 week after optic nerve crush. However, striations of RNFL became uniformly darker and thinner 2 weeks after the crush and were barely visible 4 weeks after the crush. The Delta F value was unchanged 1 week after the crush, but then decreased significantly and progressively after the second week. Delta F was unchanged in the control eyes during the experimental period. The Delta F value correlated significantly with the histologically determined RNFL thickness. CONCLUSIONS. SLO is a useful and valuable tool for in vivo imaging and quantitative evaluation of rat RNFL.