Visible Light Optical Coherence Tomography (OCT) Quantifies Subcellular Contributions to Outer Retinal Band 4

Abstract

Purpose To use visible light optical coherence tomography (OCT) to investigate subcellular reflectivity contributions to the outermost (4th) of the retinal hyperreflective bands visualized by current clinical near-infrared (NIR) OCT. Methods Visible light OCT, with 1.0 µm axial resolution, was performed in 28 eyes of 19 human subjects (21–57 years old) without history of ocular pathology. Two foveal and three extrafoveal hyperreflective zones were consistently depicted within band 4 in all eyes. The two outermost hyperreflective bands, occasionally visualized by NIR OCT, were presumed to be the retinal pigment epithelium (RPE) and Bruch's membrane (BM). RPE thickness, BM thickness, and RPE interior reflectivity were quantified topographically across the macula. Results A method for correcting RPE multiple scattering tails was found to both improve the Gaussian goodness-of-fit for the BM intensity profile and reduce the coefficient of variation of BM thickness in vivo. No major topographical differences in macular BM thickness were noted. RPE thickness decreased with increasing eccentricity. Visible light OCT signal intensity in the RPE was weighted to the apical side and attenuated more across the RPE in the fovea than peripherally. Conclusions Morphometry of the presumed RPE and BM bands is consistent with known anatomy. Weighting of RPE reflectivity toward the apical side suggests that melanosomes are the predominant contributors to RPE backscattering and signal attenuation in young eyes. Translational Relevance By enabling morphometric analysis of the RPE and BM, visible light OCT deciphers the main reflectivity contributions to outer retinal band 4, commonly visualized by commercial OCT systems.

Subcellular Comparison of Visible-Light Optical Coherence Tomography and Electron Microscopy in the Mouse Outer Retina

“… 63 Although it is generally acknowledged that melanosomes with melanin are a dominant source of RPE reflectivity, 36 , 64 – 68 the contributions of mitochondria and phagosomes have been debated. 61 As visible-light OCT now visualizes and quantifies multiple sub-bands within and around the RPE, 15 , 69 a thorough investigation of this band is warranted.…”

“… 13 These features are best exemplified in visible-light OCT, where numerous bands in the photoreceptors and retinal pigment epithelium (RPE)–Bruch's membrane (BM) complex have emerged. 14 , 15 As new bands appear, the question of their interpretation arises and controversies ensue. 16 , 17 Immunohistochemical markers may localize to a band, 18 but refractive index variations that give rise to backscattering and backreflection are most relevant for OCT. 19 Clinical relevance demands that we pinpoint the actual sources of OCT reflectivity.…”

The Development and Clinical Application of Innovative Optical Ophthalmic Imaging Techniques

“…The OCT-A is an example of a modality that greatly benefits from multimodal imaging. Although it provides significant clinical utility through its ability to capture the vasculature of the retina, limitations in the acquisition speed of OCT-A create prolonged susceptibility to motion artifacts, and other reductions (3,195,196,252,255,265,308,312,(499)(500)(501)(502)(503)(504)(505)(506). in image quality.…”

Balanced-detection visible-light optical coherence tomography

“…4C and 4D, respectively. makes the retinal anatomical features hard to be distinguished, the BD B-scan image resolved all the fine anatomical details [10,29] against the background, as highlighted in Fig. 4F.…”

“…Combining high axial resolution with increased tissue scattering contrast from visible-light, vis-OCT reveals or enhances retinal structures previously inaccessible by NIR OCT. Recent studies have found that vis-OCT can delineate Bruch's membrane (BM) [8][9][10], a structural origin of macular degeneration, and the inner plexiform layer (IPL) sublayers [11,12], which contains scattering information from dendritic connections that may be a biomarker for glaucoma. Additionally, vis-OCT achieved retinal oximetry by analyzing spectral contrast between oxygenated and deoxygenated blood [13], opening a new window for functional retinal imaging.…”