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Florian Beer, Andreas Wartak, Niklas Pircher, Stephan Holzer, Jan Lammer, Gerald Schmidinger, Bernhard Baumann, Michael Pircher, Christoph K. Hitzenberger; Mapping of Corneal Layer Thicknesses With Polarization-Sensitive Optical Coherence Tomography Using a Conical Scan Pattern. Invest. Ophthalmol. Vis. Sci. 2018;59(13):5579-5588. doi: https://doi.org/10.1167/iovs.18-25311.
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We demonstrate segmentation and mapping of corneal layers (epithelium, Bowman's layer, and stroma) across the entire cornea (limbus to limbus), using additional contrast provided by polarization-sensitive optical coherence tomography (PS-OCT) and analyze the reproducibility of the procedure.
A custom built PS-OCT system operating at 1045 nm central wavelength with conical scanning was used for image acquisition. Conical scanning allows for almost perpendicular beam incidence on the corneal surface and provides good signal quality over the entire field of view. Epithelium, Bowman's layer, and stroma were segmented using the additional contrast provided by PS-OCT. Thickness maps were computed and analyzed in sectors. Both eyes of 20 healthy volunteers were imaged at least three times to test this method and to quantify reproducibility.
Thickness maps of the epithelium show significant (P < 0.001) superior thinning and an inferior thickening. Bowman's layer appears homogeneous within the central 7 to 8 mm diameter of the cornea and gets thinner toward the periphery until this layer disappears between 4 and 5.5 mm eccentricity from the center. Intersubject variations of the measured thicknesses of epithelium (coefficient of variation [CV] ∼8%), Bowman's layer (CV∼25%), and stroma (CV∼10%) were observed. Very good reproducibility of thickness measurements of epithelium (CV < 3%), Bowman's layer (CV < 5%), and stroma (CV < 2%) was found. Furthermore, a significant correlation (P < 0.001) between layer thicknesses of the right and left eyes of the same subject was found.
PS-OCT with conical scanning is a feasible approach for determining thickness maps of corneal layers on a large field of view with high reproducibility.
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