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Hessam Roodaki, Wei-Jun Chen, Daniel Zapp, Abouzar Eslami; Simulated keratometry using microscope-integrated optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2128.
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Intraoperative simulated keratometry has the potential to have a positive impact on anterior segment surgeries. Microscope-integrated Optical Coherence Tomography (OCT) is one of the modalities that can be employed for that purpose. This study compares astigmatism measurements by a gold standard method and measurements by an ophthalmic surgical microscope with a modified OCT engine in a porcine wet lab.
A Lumera 700 microscope with RESCAN 700 (Zeiss, Oberkochen, Germany) is modified and equipped with an automated algorithm to carry out simulated keratometry. The process starts with centering the OCT scan region to the corneal vertex. Then, an OCT volume covering a region of 6mm (width) × 6mm (height) × 2mm (depth) is captured from ex-vivo porcine eyes. Additional B-scans are captured and used for the correction of motions induced by environmental effects. The algorithm then segments the cornea in the motion-corrected volume. To measure the astigmatism of the corneal surface, anterior axial power map is calculated and the simulated keratometry values of the flattest and the steepest meridians are extracted. The difference between the two k-readings is considered as the measured astigmatism. The corneal topography and astigmatism of each porcine eye is also measured using an ATLAS 9000 corneal topography system (Zeiss, Dublin, USA).
20 porcine eyes are tested for the purpose of this study. To eliminate measurement inaccuracies, each eye is tested 5 times with each method and the median reading is used. 5 eyes are rejected due to inconsistent measurements. The calculated central astigmatism in each eye is compared to the reference measurements by ATLAS 9000. The readings have a correlation coefficient of 0.67. The observed deviation between the values by the proposed method and the reference method has a mean of 0.62, a standard deviation of 0.41, and a median of 0.57 (all in diopters).
Our results show that astigmatism measurements using microscope-integrated OCT is comparable to the measurements using the gold standard method with a correlation coefficient of 0.67. Further research is needed to examine the repeatability of measurements using the proposed method.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Anterior axial power maps of an ex-vivo porcine eye calculated by the proposed method (a) and the gold standard method (b).
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