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Pablo Perez-Merino, Sergio Ortiz, Nicolas Alejandre-Alba, Alberto de Castro, Ignacio Jimenez-Alfaro, Susana Marcos; OCT-based Topography Corneal Aberrations And Ray Tracing Total Aberrations In Keratoconus Before And After Intracorneal Ring Treatment. Invest. Ophthalmol. Vis. Sci. 2012;53(14):97.
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© ARVO (1962-2015); The Authors (2016-present)
To analyze corneal and total aberrations of keratoconic eyes, before and after intracorneal ring segments (ICRS) implantation, using custom-developed corneal topography based on spectral domain optical coherence tomography (OCT) and laser ray tracing (LRT).
Corneal and total aberrations were measured on 8 keratoconic eyes pre-operatively and at 3 months post-op. ICRS (Ferrara-type) were implanted following surgical standards (femtosecond). 3D images were obtained with a custom-sOCT. The system was provided with custom algorithms for denoising and segmentation of the images, as well as fan (scanning) and optical (refraction) distortion correction algorithms to provide fully quantitative images of the anterior and posterior corneal surfaces. Algorithms were developed for analysis of corneal elevation maps (biconicoid and Zernike fitting), and pachymetry. The pupil center reference was calculated from the segmented iris volume, fixed reference for post-ICRS analysis. Corneal aberrations were estimated using ray tracing from 3D OCT anterior and posterior elevations in ZEMAX. Total aberrations were measured with a custom-LRT. Measurements were performed over a 4 mm effective pupil diameter.
Keratoconic eyes showed high amounts of higher order aberrations (HOAs) (0.68 ± 0.36 μm, corneal; 0.57 ± 0.45 μm, total), particularly coma-like terms (1.24 ± 0.69 μm, corneal; 0.94 ± 0.31μm, total), and astigmatism (0.25 ± 0.11μm, corneal; 0.37 ± 0.51μm, total). Both corneal and total aberrations were reduced which were reduced by ~15% 3 months post-ICRS. The posterior corneal surface contributed by 14% to the corneal aberrations. Corneal and total aberrations were correlated both pre-op (83%) and post-ICRS (71%), indicating a predominant role of corneal aberrations in these eyes.
ICRS produced a reduction of coma and astigmatism in keratoconic patients, although a high intersubject variability to the response of ICRS is observed in both, corneal and total aberrations. Corneal aberrations can be accurately evaluated from anterior and posterior surface shapes estimated from anterior segment sOCT. With appropriate correction of fan and optical distortion, sOCT is an excellent technology for the evaluation of ICRS implantation and its optical outcomes.
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