Abstract
Custom high-resolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT) was used to characterize three-dimensionally (3-D) corneal topography in keratoconus before and after implantation of intracorneal ring segments (ICRS). Previously described acquisition protocols were followed to minimize the impact of the motions of the eye. The collected set of images was corrected from distortions: fan (scanning) and optical (refraction). Custom algorithms were developed for automatic detection and classification of volumes in the anterior segment of the eye, in particular for the detection and classification of the implanted ICRS. Surfaces were automatically detected for quantitative analysis of the corneal elevation maps (fitted by biconicoids and Zernike polynomials) and pachymetry. Automatic tools were developed for the estimation of the 3-D positioning of the ICRS. The pupil center reference was estimated from the segmented iris volume. The developed algorithms are illustrated in a keratoconic eye (grade III) pre- and 30 days post-operatively after implantation of two triangular-section, 0.3-mm thick Ferrara ring segments. Quantitative corneal topographies reveal that the ICRS produced a flattening of the anterior surface, a steepening of the posterior surface, meridional differences in the changes in curvature and asphericity, and increased symmetry of the anterior topography. Optical distortion correction through the ICRS (of a different refractive index from the cornea) allowed accurate pachymetric estimates, which showed increased thickness in the ectatic area as well as in peripheral corneal areas. Automatic tools allowed estimation of the depth of the implanted ICRS ring, as well as its rotation with respect to the pupil plane. Anterior segment sOCT provided with fan and optical distortion correction and analysis tools is an excellent instrument for evaluating and monitoring keratoconic eyes and for the quantification of the changes produced by ICRS treatment.
Highlights
Keratoconus is a bilateral, asymmetric and chronic disease of the eye caused by the weakening of the cornea with a prevalence of 1 per 2000 in the population [1]
Quantitative corneal topographies reveal that the intracorneal ring segments (ICRS) produced a flattening of the anterior surface, a steepening of the posterior surface, meridional differences in the changes in curvature and asphericity, and increased symmetry of the anterior topography
Anterior segment sOCT provided with fan and optical distortion correction and analysis tools is an excellent instrument for evaluating and monitoring keratoconic eyes and for the quantification of the changes produced by ICRS treatment
Summary
Keratoconus is a bilateral, asymmetric and chronic disease of the eye caused by the weakening of the cornea with a prevalence of 1 per 2000 in the population [1]. It is characterized by a progressive thinning and steepening of the cornea, resulting in a coneshaped cornea, which leads to increased astigmatism and high order aberrations [2], and a loss of visual quality [3]. The progressive corneal thinning and steepening usually results in the need of corneal transplant in advanced stages [5,6]. One of the advantages of the ICRS surgery is the possibility of reshaping the cornea without removing tissue, a potential drawback is the lack of predictability of its outcomes [13,14,15]
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