Visible and near-infrared imaging of the nerve fiber layer of the isolated rat retina

Purpose: To develop an isolated rat retina preparation suitable for the study of the reflectance of the mammalian retinal nerve fiber layer (RNFL). Methods: A rat retina with a short piece of optic nerve attached was dissected free from the eye and stretched over a slit in a black membrane. The retina was placed in a black chamber perfused with warmed and oxygenated physiologic solution. Imaging microreflectometry was used to acquire images of the RNFL at wavelengths from 400 to 830 nm and over time. Results: At all wavelengths the isolated retina provided high-contrast images of nerve fiber bundles against a uniform, dark background. The nerve fiber bundles had a speckled texture, especially at long wavelengths. Time-lapse movies showed that over a period of several minutes the speckle pattern slowly changed. Although the general appearance of the bundles was similar at two closely spaced wavelengths (660 and 680 nm), the detailed patterns were completely different. Conclusion: The isolated retina preparation is well suited to the study of the optical properties of the RNFL. The speckled texture of nerve fiber bundles probably results from optical interference in the scattered light. Thr slow change in pattern implies that the size and/or shape of the scattering structures must change with time.