Band Visibility in High-Resolution Optical Coherence Tomography Assessed With a Custom Review Tool and Updated, Histology-Derived Nomenclature

Abstract

Purpose: For structure-function research at the transition of aging to age-related macular degeneration, we refined the current consensus optical coherence tomography (OCT) nomenclature and evaluated a novel review software for investigational high-resolution OCT imaging (HR-OCT; <3 µm axial resolution).

Method: Volume electron microscopy, immunolocalizations, histology, and investigational devices informed a refined OCT nomenclature for a custom ImageJ-based review tool to assess retinal band visibility. We examined effects on retinal band visibility of automated real-time averaging (ART) 9 and 100 (11 eyes of 10 healthy young adults), aging (10 young vs 22 healthy aged), and age-related macular degeneration (AMD; 22 healthy aged, 17 early (e)AMD, 15 intermediate (i)AMD). Intrareader reliability was assessed.

Results: Bands not included in consensus nomenclature are now visible using HR-OCT: inner plexiform layer (IPL) 1-5, outer plexiform layer (OPL) 1-2, outer segment interdigitation zone 1-2 (OSIZ, including hyporeflective outer segments), and retinal pigment epithelium (RPE) 1-5. Cohen's kappa was 0.54-0.88 for inner and 0.67-0.83 for outer retinal bands in a subset of 10 eyes. IPL-3-5 and OPL-2 visibility benefitted from increased ART. OSIZ-2 and RPE-1,2,3,5 visibility was worse in aged eyes than in young eyes. OSIZ-1-2, RPE-1, and RPE-5 visibility decreased in eAMD and iAMD compared to healthy aged eyes.

Conclusions: We reliably identified 28 retinal bands using a novel review tool for HR-OCT. Image averaging improved inner retinal band visibility. Aging and AMD development impacted outer retinal band visibility.

Translational significance: Detailed knowledge of anatomic structures visible on OCT will enhance precision in research, including AI training and structure-function analyses.

Figure 1.

Simplified presentation of the proposed High-Resolution Optical Coherence Tomography nomenclature. Overview of the retinal bands and boundaries for the proposed HR-OCT nomenclature. A total of 28 retinal bands (including the vitreous and the sclera) and 27 boundaries are included. Photoreceptors range from OPL-1 to OSIZ-2. Post-receptoral retina contains bipolar cells and ganglion cells, which form multiple parallel pathways to the brain, represented by bands between ILM and INL; these bands also contain horizontal cells and amacrine cells that modulate signals along these pathways. The inner retina (blue) combines all layers from the ILM to the OPL-2, which are supplied by the vascular plexuses; these have a barrier function analogous to the cerebral vasculature. The outer retina (teal, green, yellow) contains all bands from the OPL-2 to Bruch membrane, representing cells supplied by the choroid (orange), a specialized bed of systemic circulation. BM, Bruch membrane; CC, choriocapillaris; CH, choroid. GCL, ganglion cell layer; HFL, Henle fiber layer; IPL, inner plexiform layer; ILM, internal limiting membrane; MZ, myoid zone; NFL, nerve fiber layer; OPL, outer plexiform layer; ONL, outer nuclear layer; VRI: Vitreoretinal interface.

Figure 2.

Presentation of the proposed high-resolution optical coherence tomography nomenclature in a healthy young eye. An exemplary representation of the proposed high-resolution optical coherence tomography nomenclature in the left eye of a 34-year-old healthy male, automated real-time averaging set to 100. The red frame is 20 A-scans wide (∼200 µm). The yellow lines within the red frame indicate the location of 3 A-scans used to compute the red longitudinal reflectivity profile. Reflectivity is measured as gray values [A.U.], in which 0 is black and 255 is white. Panels at right and far-right are magnified 150% and 200%, respectively. White and black rectangles show which IPL bands were graded as hyper- (white) and hypo- (black) reflective. Although the distinct retinal bands can be identified on the B-scan and even more so in the enlarged view, it is more difficult to do so by only relying on the LRP. The yellow lines at the foveal center highlight the location of the central bouquet, the area of highest density of cone photoreceptors and Müller cells. BM, Bruch membrane; CC, choriocapillaris; CH, choroid; GCL, ganglion cell layer; HFL, Henle fiber layer; IPL, inner plexiform layer; ILM, internal limiting membrane; MZ, myoid zone; NFL, nerve fiber layer; OPL, outer plexiform layer; ONL, outer nuclear layer.

Figure 3.

Presentation of the proposed high-resolution optical coherence tomography nomenclature in a healthy aged eye. An exemplary representation of the proposed high-resolution optical coherence tomography nomenclature in the left eye of a 65-year-old healthy female, automated real-time averaging set to 9. The red frame is 20 A-scans wide (∼200 µm). The yellow lines within the red frame indicate the location of three A-scans used to compute the red longitudinal reflectivity profile. Reflectivity is measured as gray values [A.U.], in which 0 is black and 255 is white. Panels at right and far-right are magnified 150% and 200%, respectively. Although the distinct retinal bands can be identified on the B-scan and even more so in the enlarged view, it is more difficult to do so by only relying on the LRP. Still, in this exemplary case, five bands were not identifiable (listed at bottom right corner). The yellow lines at the foveal center highlight the location of the central bouquet, the area of highest density of cone photoreceptors and Müller cells. Note that the yellow lines are oriented according to the external fovea (e.g., the rise of the ELM), which does not match the internal fovea (lowest point of the foveal depression), in this case. This common occurrence will be explored separately. BM, Bruch membrane; CC, choriocapillaris; CH, choroid; GCL, ganglion cell layer; HFL, Henle fiber layer; ILM, internal limiting membrane; IPL, inner plexiform layer; MZ, myoid zone; NFL, nerve fiber layer; ONL, outer nuclear layer; OPL, outer plexiform layer.

Figure 4.

Presentation of the proposed high-resolution optical coherence tomography nomenclature in an eAMD eye. An exemplary representation of the proposed high-resolution optical coherence tomography nomenclature in the left eye of a 71-year-old female eAMD patient, automated real-time averaging set to 9. The inset is 20 A-scans wide (∼200 µm). The yellow lines within the red frame indicate the location of 3 A-scans used to compute the red longitudinal reflectivity profile. Reflectivity is measured as gray values [A.U.], in which 0 is black and 255 is white. While the distinct retinal bands can be identified on the B-scan and even more so in the enlarged view, it is more difficult to do so by only relying on the LRP. In this exemplary case, five bands were not identifiable (listed at bottom right corner). The yellow lines at the foveal center highlight the location of the central bouquet, the area of highest density of cone photoreceptors and Müller cells, as signified by the inward rise of the ELM. BM, Bruch membrane; CC, choriocapillaris; CH, choroid; GCL, ganglion cell layer; HFL, Henle fiber layer; IPL, inner plexiform layer; ILM, internal limiting membrane; MZ, myoid zone; NFL, nerve fiber layer; ONL, outer nuclear layer; OSIZ, outer segment interdigitation zone.

Figure 5.

Presentation of the proposed High-Resolution Optical Coherence Tomography nomenclature in an iAMD eye. An exemplary representation of the proposed High-Resolution Optical Coherence Tomography nomenclature in the left eye of a 70-year-old male iAMD patient, automated real-time averaging set to 9. The red frame is 20 A-scans wide (∼200 µm). Panels at right and far-right are magnified 150% and 200%, respectively. The yellow lines within the red frame indicate the location of three A-scans used to compute the red longitudinal reflectivity profile. Reflectivity is measured as gray values [A.U.], in which 0 is black and 255 is white. Although the distinct retinal bands can be identified on the B-scan and even more so in the enlarged view, it is more difficult to do so by only relying on the LRP. In this exemplary case, five bands were not identifiable (listed at bottom right corner). The yellow lines at the foveal center highlight the location of the central bouquet, the area of highest density of cone photoreceptors and Müller cells. BM, Bruch membrane; CC, choriocapillaris; CH, choroid GCL, ganglion cell layer; HFL, Henle fiber layer; IPL, inner plexiform layer; ILM, internal limiting membrane; MZ, myoid zone; NFL, nerve fiber layer; ONL, outer nuclear layer; OPL, outer plexiform layer.

Figure 6.

Step-by-Step guide through the custom ImageJ plug-in. Left eye of a 34-year-old male, ART 100. A1 – A5 show the first panels appearing after initiating the High-Res OCT review plug-in. A1 shows the IR localizer image. The red line indicates the position of the OCT B-scan at the 5° superior retina. A2 shows the OCT B-scan indicated in A1 at its original size. A3 is a magnified view (300%) of the inset in A2, which is the preferred grading magnification. A4 shows the longitudinal reflectivity profile of the respective grading location. A5 indicates the retinal boundary to be assessed (VRI, blue arrowhead) and allows for qualitative evaluation of retinal boundary visibility on the B-scan (A3, options: Continuous, discontinuous, not visible, not present, uncertain) and the longitudinal reflectivity profile (A4, options: Visible, split, not visible, not present). The orange arrowhead in A4 shows the grading location on the X-axis. Crosshairs in all images (red arrowheads) allow for a simultaneous assessment of a retinal location in the IR image, the OCT, and the LRP. To lock in the position of a boundary, the crosshair needs to be moved to the posterior boundary of the retinal band in question. Hitting “OK“ in panel A5 saves the assessment for the respective horizontal and vertical position. After grading all retinal band boundaries in one location, the plug-in will move to the next location and the grading process will re-commence. B1–B5 show the same panels as A1–A5, although at the foveal center. The green arrowhead in B4 highlights the retinal band boundary in question. High-Res OCT, high-resolution optical coherence tomography; IR, infrared; VRI, vitreoretinal interface.

Figure 7.

Distribution of the grading locations at 5° superior retina and fovea. Graphical presentation of the 9 grading locations at (A) the foveal center and (B) 5° superior retina in the left eye of a 31-year-old male, ART 100. The distance of the grading locations to the foveal center is shown in mm. The gray lines indicate the extent of the ETDRS central subfield (1 mm diameter), the inner ring (3 mm diameter), and the outer ring (6 mm diameter). To improve visibility, the OCT scan was straightened along Bruch membrane, consequently, hypertransmission trails appear non-axial.

Figure 8.

Harmonization of schemes for retinal pigment epithelium based on organelle distribution in volume electron microscopy. (A) Distribution of organelles in a single parafoveal RPE cell body of a 21-year-old male organ donor, as reconstructed by deep-learning assisted volume electron microscopy. Apical processes are excluded. ED (electron-dense) organelles included lipofuscin, melanolipofuscin, and melanosomes. Y-axis shows depth along an apical-basal vertical axis, expressed as µm apical (+) or basal (−) to the actin cytoskeletal belt. Dashed lines indicate the approximate locations of apical border of the cell body, actin cytoskeletal belt, and basal lamina. X-axis shows average cross-section areas of organelles in µm². Reproduced with slight modification from Lindell et al. (B) Juxtaposed are corresponding band names in the presented nomenclature and the literature,^,, as well as their reflectivity (HYPERreflective or HYPOreflective).