Visualization of Henle’S Fiber Layer in Macular Pathology Using SDOCT

Abstract

Purpose: : Spectral Domain Optical Coherence Tomography (SDOCT) indirectly measures the reflectivity of infrared light through the depth of the retina along a path originating from its pupil entry position. Henle’s fiber layer (HFL) is made up of Muller cells and photoreceptor axons coursing obliquely from their nuclei towards their synapse with inner nuclear cells. Because of their directional reflectivity they can be distinguished from the optical outer nuclear and outer plexiform layers. Here we sought to illustrate how various retinal pathologies alter HFL by optical effects which reciprocate variations of the pupil entry position in normals.

Methods: : Horizontal and vertical frame averaged SDOCT images were performed on 28 normal right eyes and 25 normal left eyes. Images were obtained from pupil positions where B-scans appeared "flat" and at the extremes of good quality pupil positions. Images were registered to each other such that HFL displayed sharp contrast from the adjacent outer nuclear layer across the length of the scans and were manually segmented. The average contribution of Henle’s fiber layer to the distance between the external limiting membrane and the outer plexiform layer was measured along the lengths of the scan. A retrospective review of 2904 consecutive eyes imaged with SDOCT was performed and cases demonstrating reflectivity changes in HFL were identified and classified.

Results: : HFL thickness constituted 30-50% of thickness previously ascribed to the ONL and had demonstrated directional reflectivity varying the position of the SDOCT entrance beam. As expected from their effect on the geometry of HFL, certain macular pathologies cause a significant change in tissue reflectivity at 25% thickness that corresponds to HFL. These can be broken into distinct groups which each distort the angle of incident light on HFL: Vitreoretinal interface disorders, RPE deformations, and outer retinal degenerations.

Conclusions: : Recognition of the ability to visualize the contribution of Henle's fiber layer to SDOCT images of the outer retina in normal subjects provides a framework for an optical model explaining HFL visualization in various retinal pathologies.

Keywords: imaging/image analysis: clinical • retina • anatomy