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Alice Liu, Jianwei David Li, Ryan P McNabb, Cynthia Toth, Joseph Izatt, Anthony N Kuo; Microscope-Integrated OCT-Based Topography Maps for Corneal Astigmatism Assessment. Invest. Ophthalmol. Vis. Sci. 2020;61(7):4313.
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© ARVO (1962-2015); The Authors (2016-present)
Assessing corneal astigmatism intraoperatively is key to providing good post-surgical refractive outcomes. As an example, there are limited tools to assess astigmatism in corneal transplants intraoperatively, and hence after penetrating keratoplasty, 15-31% of these patients have astigmatism greater than 5 diopters (D) [Feize S, et al. J Ophthalmol. 2011]. To help address this issue, we developed Microscope-Integrated OCT (MIOCT)-based topography with the potential to give surgeons intraoperative, quantitative corneal astigmatism information. In previous work, we described the assessment of astigmatism ≥ 6 D [Tian J, et al. ARVO E-Abstract 2018]. We describe here the detection of astigmatism below 6 D in reference phantom corneas.
Plastic, custom-printed phantom corneas with known astigmatisms spanning 0.0 – 6.0 D were imaged using MIOCT consisting of a research 200 kHz 1040 nm swept source engine integrated into a commercial surgical microscope (Leica Proveo 8). The phantoms were designed to have curvatures spanning physiologic corneal curvatures. Each radial OCT volume was 1444 x 700 x 36 (depth x Ascan x Bscan). After an initial manual pilot segmentation of the first frame, each Bscan was then automatically segmented to detect epithelial boundaries, resampled to a 6th order Zernike function, and corrected for system-specific distortions. Axial curvatures were calculated according to ANSI standards. Curvatures within the 3-mm optical zone were then used to calculate the magnitude of astigmatism for comparison with the known references.
The mean absolute paired differences in astigmatism between our method and the known reference values was 0.80 D. Differences were tested using the Wilcoxon Signed-Rank Test and found to not be statistically significant (p=0.5781). A sample corneal topography map created from MIOCT data is shown in Fig 1.
We assessed our MIOCT-based corneal topography on custom-printed reference cornea phantoms and were able to achieve accuracy within 1 D. This system has potential for intraoperative astigmatism management, particularly for full-thickness corneal transplantations.
This is a 2020 ARVO Annual Meeting abstract.
Figure 1: A) Corneal phantoms spanning 0.0-6.0 diopters. B) Sample topography map of a 3-diopter astigmatic phantom cornea.
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