Abstract
purpose. The peripapillary retinal nerve fiber layer (RNFL) thickness pattern in the normal human eye has been well characterized using data obtained with scanning laser polarimetry and optical coherence tomography. The authors sought to characterize the normative peripapillary RNFL thickness and pattern using histologic sections obtained from healthy postmortem human eyes.
methods. Seventeen unpaired normal postmortem eyes were recruited into this study. Each eye was sectioned using the “umbrella technique” to obtain four concentric peripapillary rings, each centered on the optic disc, with diameters of 3.0, 3.5, 4.0, and 4.5 mm. RNFL thickness data along each ring section was measured at 100 equidistant locations. Thickness data, for each ring diameter, across all eyes were averaged to arrive at normative thickness values for the peripapillary RNFL thickness in eyes processed using this technique.
results. Average RNFL thicknesses (±SD) for the 3.5-mm diameter ring were as follows: overall, 60.3 ± 19.5 μm; superior, 75.3 ± 26.5 μm; inferior, 69.4 ± 22.4 μm; nasal, 48.1 ± 15 μm; temporal, 49.2 ± 26.4 μm. Qualitatively, the RNFL thickness showed a double-hump pattern with relatively similar superior and inferior peaks and with temporal and nasal troughs. Progressively larger peripapillary rings showed progressively thinner RNFL thickness at all quadrants. In contrast, the relative thickness percentage for each quadrant remained unchanged among the four different diameter rings.
conclusions. Histologic data from a group of healthy postmortem eyes demonstrate the pattern of RNFL thickness in normal eyes. These data corroborate imaging findings of peripapillary RNFL thickness patterns obtained using commercially available RNFL imaging devices.
In healthy eyes, the peripapillary RNFL thickness pattern around the optic disc shows a unique pattern, with two peaks (superior and inferior) and two troughs (temporal and nasal).
1 Significant variability exists among healthy persons, as evident by the scatter seen in the normative range plots of two imaging devices (Stratus OCT and GDx-VCC; Carl Zeiss Meditec Inc., Dublin, CA;
Fig. 1 ). The graphical representation of the circumpapillary RNFL thickness is often referred to as a temporal-superior-nasal-inferior-temporal (TSNIT) graph and is classically described as a “double-hump” pattern.
2 The shape the RNFL thickness pattern assumes, as apparent in the TSNIT graph, is referred to as the RNFL thickness modulation around the optic disc.
Much of what we know about RNFL modulation in the human eye is derived from in vivo imaging studies, primarily using scanning laser polarimetry (SLP) and optical coherence tomography (OCT). In addition, few histologic studies have been performed on humans
3 4 and primates.
5 6 7 8 However, the data presented in these studies are insufficient to validate the data derived from imaging devices
1 because of the few measurement points obtained for each processed eye and the different histologic approaches used in each of these studies.
In this study, histologic data in the form of 100 equidistant data points collected at four concentric peripapillary diameters were used to plot the modulation of the RNFL thickness pattern in normal human postmortem eyes.