Knighton R W, Baverez C, Bhattacharya A
Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami School of Medicine, FL 33101.
Invest Ophthalmol Vis Sci. 1992 Aug;33(9):2603-11.
Various optical methods for assessing the retinal nerve fiber layer (RNFL) depend on reflected light, but little is known about the characteristics of the RNFL as a reflecting structure. The authors investigated the angular dependence of light reflected by the unmyelinated nerve fibers of the toad eyecup using a small 500-nm light source that could illuminate the retina from various directions and a movable low-power microscope that imaged the retina onto a cooled charge-coupled device in a digital camera system. Measured areas had nerve fiber bundles separated by gaps. Therefore, the reflectance of a bundle alone could be determined from the difference in intensity between the bundle and an adjacent gap. The RNFL reflectance showed striking directional dependence; nerve fiber bundles seen when illuminated from one direction disappeared completely when illuminated from another. Light reflected by a bundle was confined to a conical sheet concentric with the axis of the bundle. The apex angle of the cone was twice the angle between the incident light and the bundle axis, and the orientation of the cone changed with the orientation of the RNFL. This behavior was consistent with the theory of light scattering by cylinders. Therefore, it was concluded that the RNFL reflectance arises from cylindric structures. These results have clinical significance for imaging the RNFL in the human eye because the apparent intensity of the RNFL will depend, not just on its thickness, but also on its orientation relative to the imaging system.
各种用于评估视网膜神经纤维层（RNFL）的光学方法都依赖于反射光，但对于RNFL作为一种反射结构的特性却知之甚少。作者使用一个小型500纳米光源和一个可移动的低功率显微镜，研究了蟾蜍眼杯无髓神经纤维反射光的角度依赖性。该光源可以从不同方向照亮视网膜，显微镜则将视网膜成像到数码相机系统中的冷却电荷耦合器件上。所测量的区域中神经纤维束被间隙隔开。因此，仅通过一束纤维与相邻间隙之间强度的差异就可以确定该纤维束的反射率。RNFL反射率表现出显著的方向依赖性；从一个方向照射时可见的神经纤维束，从另一个方向照射时则完全消失。一束纤维反射的光被限制在与该纤维束轴同心的锥形薄片内。圆锥的顶角是入射光与纤维束轴之间夹角的两倍，并且圆锥的方向会随着RNFL的方向而改变。这种行为与圆柱体光散射理论一致。因此，可以得出结论，RNFL反射率源于圆柱形结构。这些结果对于人眼RNFL成像具有临床意义，因为RNFL的表观强度不仅取决于其厚度，还取决于其相对于成像系统的方向。
