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Rishi Subrahmanyan, Alice Liu, William Raynor, Jianwei David Li, Ryan P McNabb, Cynthia A Toth, Joseph Izatt, Anthony N Kuo; MIOCT-generated topography maps for astigmatism magnitude and axis calculation in corneal phantoms. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2017.
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© ARVO (1962-2015); The Authors (2016-present)
Corneal surgeries such as penetrating keratoplasty (PKP) can result in significant postoperative refractive errors that are difficult to assess intraoperatively with the current standard of care. Microscope-Integrated OCT (MIOCT) has the potential to characterize corneal astigmatism intraoperatively to help improve post PKP refractive outcomes. Here, we report accurate detection of astigmatism magnitude and axis in software-generated and 3D-printed phantom corneas.
Software phantoms were designed using MATLAB to simulate the corneal surface with astigmatism from 0 – 6 diopters (D). Plastic, 3D-printed phantom corneas were designed with astigmatism from 0 – 6 D. Four phantoms in each group have astigmatism with steep axis at 180°, and two have astigmatism with steep axis at 0° to evaluate anisotropy in imaging direction. Printed phantoms were imaged with MIOCT. After manually segmenting the first frame as a pilot, each subsequent Bscan in the volume was automatically segmented to identify the epithelial surface. Segmentations were fit to a 6th order Zernike function and corrected for system-specific distortions. Astigmatism magnitudes and axes were calculated according to ANSI standards for all phantoms.
Topography maps are shown for software (Figure 1) and 3D-printed (Figure 2) phantoms. For software phantoms, the mean absolute difference between calculated and reference astigmatism magnitude and axis was 0.012 D and 0 degrees, respectively, for phantoms with steep axis at 90° and was 0.016 D and 0 degrees, respectively, for phantoms with steep axis at 0°. For printed phantoms, the mean absolute difference between calculated and reference astigmatism magnitude and axis was 0.26 D and 2.7 degrees, respectively, for phantoms with steep axis at 90° and was 0.25 D and 8.1 degrees, respectively, for phantoms with steep axis at 0°.
We used the MIOCT-based corneal topography system on software and 3D-printed corneal phantoms to calculate astigmatism magnitude and axis. The system calculates astigmatism magnitude within approximately 0.25 D and detects axis within 10 degrees. This system has potential for intraoperative astigmatism assessment during procedures such as PKP.
This is a 2021 ARVO Annual Meeting abstract.
Software phantom topography maps. Steep (dashed) and flat (solid) axes are shown for each phantom.
3D-printed phantom topography maps. Steep (dashed) and flat (solid) axes are shown for each phantom.
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