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Rory A. Myer, Duncan A. Friedman, Jeffrey D. Messinger, Kenneth R. Sloan, Richard F. Spaide, Christine A. Curcio; Re-visiting Foveal Histology in the Age of OCT: Analysis using Whole Slide Scanning. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4031.
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Foveal structure is well documented for single histological sections through the center. Characterization in additional non-central planes could inform the interpretation of OCT volume scans. We examined the distribution of 9 foveal characteristics in stepped, high-resolution sections of normal maculae.
Maculae from 7 donor eyes (61 to 87 yr) were epoxy-embedded, sectioned at 1µm, and stained with toluidine blue. Digital sections were created via whole slide scanning and graded (1=yes, 0=no) by 2 observers for 9 features (Figure 1): 1) gap in the ganglion cell or 2) inner nuclear layer, 3) laterally spreading Henle fibers, 4) darker staining inner Henle fibers (Müller cells), 5) rod-free zone, 6) thickened outer nuclear layer, 7) cone inner fibers, 8) distinctive chromatin in central bouquet cones, and 9) external fovea. For each section the grades were totaled and compared to its distance from foveal center.
Inter-observer agreement was very good with Κ values ≥ 0.75 for all parameters except the central bouquet chromatin (Κ = 0.5). All sections’ grades correlated well with their distances from foveal center (Pearson’s r: -0.81 to -1.00). Sections nearest foveal center all scored 7-9, indicating that nearly all characteristics were present in all eyes. Sections further from foveal center had fewer distinguishing characteristics. For all eyes sections scored 0-1 by 150-320 µm from center. Layer thicknesses to be measured in outlying sections will characterize the Henle fiber layer.
Macular tissue sections near foveal center can be sequenced using 9 parameters, which expand the range of fovea-associated morphology. Because some of these features are not visible by current generation OCT, our observations may provide benchmarks for this evolving technology. Whole slide scanning informs OCT interpretation by allowing histology to be viewed with the same flexibility as clinical images.
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