Directional Optical Coherence Tomography Provides Accurate Outer Nuclear Layer and Henle Fiber Layer Measurements

Abstract

Purpose The outer nuclear layer (ONL) contains photoreceptor nuclei, and its thickness is an important biomarker for retinal degenerations. Accurate ONL thickness measurements are obscured in standard optical coherence tomography (OCT) images because of Henle fiber layer (HFL). Improved differentiation of the ONL and HFL boundary is made possible by using Directional OCT (D-OCT), a method that purposefully varies the pupil entrance position of the OCT beam. Methods Fifty-seven normal eyes were imaged using multiple pupil entry positions with a commercial SDOCT system. Cross-sectional image sets were registered to each other, and segmented at the top of HFL, the border of HFL and the ONL and at the external limiting membrane. Thicknesses of the ONL and HFL were measured and analyzed. Results The true ONL and HFL thicknesses varied substantially by eccentricity and between individuals. The true macular ONL thickness comprised an average of 54.6% of measurements that also included HFL. The ONL and HFL thicknesses at specific retinal eccentricities were poorly correlated. Conclusion Accurate ONL and HFL thickness measurements are made possible by the optical contrast of D-OCT. Distinguishing these individual layers can improve clinical trial endpoints and assessment of disease progression.

The Negative Cone Mosaic: A New Manifestation of the Optical Stiles-Crawford Effect in Normal Eyes

“…Accordingly, it has been shown that extracting the asymmetric component of photoreceptor reflectance (split-detection 27 ) is a powerful means for the identification of cones in a dystrophic retina. The Henle fibers, [28][29][30] the nerve fiber layer, 31 and Gunn's dots 32 also show strong directional reflectance; hence, multiangle imaging appears as a necessary procedure for adequate interpretation of high-resolution retinal imaging.…”

Outer retinal deformity detected by optical coherence tomography in eyes with foveal hypoplasia

“…In the earlier study, widening of the ONL was considered as the last factor determining foveal immaturity [6], and in the current study, we considered that analysis of the outer retinal layers (OPL+HFL+ONL) could allow a more precise evaluation of eyes with foveal hypoplasia exhibiting severe structural immaturity. In OCT images, the classical ONL, which extends from the end of the OPL to the external limiting membrane, can be divided into the HFL and true ONL, and this distinction results in a more precise structural analysis of the outer retina [9][10][11]. Focusing on the HFL appearance, the OCT findings can be classified into three types even in eyes with foveal hypoplasia exhibiting severe structural abnormalities (Fig.…”

Pupil tracking optical coherence tomography for precise control of pupil entry position

“…In retinal imaging systems, knowledge of the pupil entry position and scan location at the retinal plane can result in enhanced knowledge of the beam trajectory through the subject's eye that can elucidate the illumination incidence angle at the retinal plane. As discussed above, there are a variety of retinal structures that exhibit illumination directionality dependence [6][7][8][9][10][11][12][13][14][15][16]. Previous studies exploring this dependence varied the pupil entry position manually and therefore were subject to motion artifacts that hindered repeatability.…”

“…By displacing the OCT beam laterally, the collected back-scattered intensity of HFL increased on the opposite side of the foveal pit from the pupil entry offset, resulting in enhanced OCT visibility due to nearly normal illumination relative to HFL fibers in that region. Using eccentric pupil entry positions in a technique called Directional OCT, visualization of HFL enabled anatomically correct ONL thickness measurements [15,16]. However, similar to previous studies, the pupil entry position manual displacement was subject to patient motion and operator misalignment.…”