High-Resolution Optical Coherence Tomography in Healthy Individuals Provides Resolution at the Cellular and Subcellular Levels

Abstract

Purpose: To assess the clinical resolution capacities of a novel high-resolution optical coherence tomography (High-Res OCT).

Methods: Eight healthy volunteers were included in this observational study. Using the SPECTRALIS High-Res OCT device (Heidelberg Engineering, Heidelberg) macular b-scans were taken and compared with b-scans acquired with a SPECTRALIS HRA+OCT device (Heidelberg Engineering, Heidelberg). High-Res OCT scans were also compared with hematoxylin and eosin-stained sections from a human donor retina.

Results: High-Res OCT allowed identification of several retinal structures at the cellular and subcellular levels, namely, cell nuclei of ganglion cells, displaced amacrine cells, cone photoreceptors and retinal pigment epithelial cells compared with the commercial device. Rod photoreceptor nuclei were partially detectable. Localization of cell type-specific nuclei were confirmed by histological sections of human donor retina. Additionally, all three plexus of the retinal vasculature could be visualized.

Conclusions: SPECTRALIS High-Res OCT device provides improved resolution compared with the conventional SPECTRALIS HRA+OCT device and allows to identify structures at the cellular level, similar to histological sections.

Translational relevance: High-Res OCT shows improved visualization of retinal structures in healthy individuals and can be used to assess individual cells within the retina.

Figure 1.

Comparison of OCT b-scans between Spectralis HRA- and High-Res OCT devices. Macular cross-sectional b-scan taken with spectral domain OCT (Spectralis HRA-OCT) (A) and High-Res OCT (B) and close-up view corresponding to the parafoveal white box (A′, B′) showing the retinal vascular plexus. (C, D) Close-up view of BM, choriocapillaris (CC) (inner border, black line; outer border, white line) and Sattler's layer corresponding to the grey box in the foveal area. Scale bars, white, 200 µm; gray, 50 µm.

Figure 2.

Cone photoreceptor nuclei identified by High-Res OCT. Both images (A, B) show an area of the outer Early Treatment Diabetic Retinopathy Study ring. (A) OCT b-scan captured with High-Res OCT: Hyporeflective dots (arrowheads) in the ONL piercing the ELM representing the cone photoreceptor nuclei. Scale bar, 200 µm. (B) Hematoxylin and eosin–stained histological section of a human donor retina: with basophilic nuclei of rod (black and white arrowheads) and cones (black arrowheads). Scale bar, 100 µm; original magnification ×34.1.

Figure 3.

RPE nuclei identified by High-Res OCT. (A) OCT b-scan acquired with High-Res OCT showing the foveal area: Hyporeflective dots at the level of RPE correspond with RPE nuclei (arrows). Mononucleated RPE cell (black arrows), probably binucleated RPE cell (white arrow). The ELM, ellipsoid zone (EZ), interdigitation zone (IZ), RPE–BM complex, choriocapillaris (CC), and Sattler's layer are listed for guidance. (B) OCT b-scan acquired with spectral domain OCT (Spectralis HRA-OCT) representing the same area. Scale bars, 50 µm. (C) Hematoxylin and eosin–stained perifoveal histological section of a human donor retina with basophilic RPE nuclei (magenta; arrows) and underlying BM. Melanosomes and/or phagolysosomes show brown pigmentation and apical microvilli appear transparent. Original magnification ×40.

Figure 4.

Cell nuclei within ganglion cell layer and ONL. OCT b-scan imaged with High-Res OCT showing a parafoveal area: (A) Hyporeflective roundish shaped areas interpreted as ganglion cell nuclei (black arrowheads) in the ganglion cell layer (GCL), displaced amacrine cell nuclei (black and white arrowheads) in the IPL, amacrine cell nuclei (white arrowheads), bipolar cell nuclei (black arrows) and horizontal cell nuclei (white arrows) in the INL. (B) Hyporeflective dots in the inner ONL (arrowheads) interpreted as rod cell nuclei. Retinal nerve fiber layer (RNLF), outer plexiform layer (OPL) and ELM are listed for guidance. Corresponding unlabeled images (A′, B′). Scale bars, 200 µm.

Figure 5.

Retinal vascular plexus. OCT b-scan captured with spectral domain OCT (Spectralis HRA-OCT) (A) and High-Res OCT (B) showing the retinal vascular plexus in a foveal area. Scale bars, 200 µm.