College of Optometry, University of Houston, Houston, Texas, USA.
Invest Ophthalmol Vis Sci. 2011 Apr 16;52(5):2477-89. doi: 10.1167/iovs.10-6105. Print 2011 Apr.
An evaluation of the retinal nerve fiber layer (RNFL) provides important information on the health of the optic nerve. Standard measurements of the RNFL consider only thickness, but an accurate assessment should also consider axial length, size of the optic nerve head (ONH), blood vessel contribution, and distance of the scan from the ONH margin. In addition, although most primate ONHs are elliptical, the circular scan centered on the ONH is the mainstay in both clinical and research analyses. The purpose of this study was to evaluate thickness and area measures of RNFL cross sections when axial length and ONH shape are included.
Circular, raster, and radial scans of left eye optic nerves were acquired from 40 normal rhesus monkeys (Macaca mulatta) using spectral domain optical coherence tomography. The disc margin was identified by manually selecting the RPE/Bruch's membrane opening and ONH border tissue. With a pixel-to-micrometer conversion computed from a three-surface schematic eye, RNFL scans were interpolated at 300 to 600 μm (50-μm increments) from the edge of the ONH. The thickness and area of the RNFL at each distance were obtained by custom programs. Blood vessels in the RNFL were selected and removed from the overall RNFL measures.
The average RNFL thickness decreased systematically from 149 ± 12.0 μm for scans 300 μm from the disc margin to 113 ± 7.2 μm at an eccentricity of 600 μm (P < 0.05). In contrast, the cross-sectional areas of the RNFL did not vary with scan location from the disc margin (0.85 ± 0.07 mm(2) at 300 μm compared with 0.86 ± 0.06 mm(2) at 600 μm). Blood vessels accounted for 9.3% of total RNFL thickness or area, but varied with retinal location. On average, 17.6% of the superior and 14.2% of the inferior RNFL was vascular, whereas blood vessels accounted for only 2.3% of areas of the temporal and nasal RNFL regions.
In nonhuman primates, with appropriate transverse scaling and ONH shape analysis, the cross-sectional area of the RNFL is independent of scan distance, up to 600 μm from the rim margin, indicating that the axonal composition changes little over this range. The results suggest that, with incorporation of transverse scaling, the RNFL cross-sectional area, rather than RNFL thickness, provides an accurate assessment of the retinal ganglion cell axonal content within the eye.
视网膜神经纤维层（RNFL）的评估提供了视神经健康的重要信息。RNFL 的标准测量仅考虑厚度，但准确的评估还应考虑眼轴长度、视盘大小、血管贡献以及扫描与视盘边缘的距离。此外，虽然大多数灵长类动物的视盘为椭圆形，但以视盘为中心的圆形扫描仍然是临床和研究分析的主要方法。本研究旨在评估包括眼轴长度和视盘形状时 RNFL 横截面的厚度和面积测量值。
使用谱域光学相干断层扫描获取 40 只正常猕猴（Macaca mulatta）左眼视神经的圆形、光栅和放射状扫描。通过手动选择 RPE/Bruch 膜开口和视盘边界组织来识别视盘边缘。根据三表面示意图眼计算的像素到微米的转换，将 RNFL 扫描从视盘边缘以 300 至 600 μm（50-μm 增量）插值。通过自定义程序获得每个距离的 RNFL 厚度和面积。从整体 RNFL 测量值中选择并去除 RNFL 中的血管。
从距视盘边缘 300 μm 的扫描处的 149±12.0 μm 到 600 μm 处的 113±7.2 μm（P<0.05），RNFL 厚度呈系统下降。相比之下，从视盘边缘的扫描位置（300 μm 处为 0.85±0.07 mm2，600 μm 处为 0.86±0.06 mm2），RNFL 的横截面面积没有变化。血管占 RNFL 总厚度或面积的 9.3%，但随视网膜位置而变化。平均而言，上 RNFL 的 17.6%和下 RNFL 的 14.2%为血管，而血管仅占颞侧和鼻侧 RNFL 区域面积的 2.3%。
在非人类灵长类动物中，通过适当的横向缩放和视盘形状分析，RNFL 的横截面面积与扫描距离无关，在距边缘 600 μm 范围内，表明在此范围内轴突组成变化很小。结果表明，通过纳入横向缩放，RNFL 横截面面积而不是 RNFL 厚度为评估眼睛内视网膜神经节细胞轴突含量提供了更准确的评估。
