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Pablo Perez-Merino, Sergio Ortiz, Nicolas Alejandre, Alberto de Castro, Iñigo Jimenez-Alfaro, Susana Marcos; Full OCT Corneal Topography and Aberrations in Keratoconic Patients and Their Change After Intrastromal Corneal Ring Segments (ICRS) Implantation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4181.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize 3-dimensionally corneal topography and aberrations of keratoconic eyes, before and after ICRS implantation, using custom-developed OCT.
OCT corneal topography and aberrations were measured on five keratoconic eyes pre-operatively and post-operatively (7, 30 and 90 days). ICRS (Ferrara-type) were implanted. 3-D images were obtained with a high-resolution high-speed spectral domain OCT. Acquisition protocols were followed to minimize the impact of motion (360 A-scans x 50 B-scans, 12x10 mm lateral range, acquisition time<0.8s) and alignment was achieved with respect to the specular reflection. The instrument was provided with custom algorithms for denoising and segmentation of the images, as well as fan (scanning) and optical (refraction) distortion correction algorithms, to provided fully quantitative images of the anterior and posterior surfaces. Custom algorithms were developed for analysis of corneal elevation maps (biconicoid and Zernike fitting), pachymetry, and of the 3-D positioning (depth and rotation) of the ICRS. The pupil center reference was estimated from the segmented iris volume. Corneal aberrations were estimated by ray tracing from 3D OCT anterior and posterior elevations in ZEMAX.
Preoperatively, average corneal radii of curvature were 6.56 ± 0.47 mm and 5.22 ± 0.54 mm for the anterior and posterior surfaces, the thickness in the ectatic area was 414 ± 21 µm, and the RMS (diameter:3.5 mm) of astigmatism and corneal HOA was 2.78 ± 0.84 µm. ICRS implantation produced a significant flattening of the corneal surfaces (anterior: 6.78 ± 0.41 mm, posterior: 5.65 ± 0.56 mm), a redistribution of thickness within the optical zone (minimum thickness: 429 ± 31 µm), and decreased of corneal aberrations (~33%). The ICRS were measured to be placed at a depth of 353 ± 25 µm showing a rotation of 9 ± 5º.
Anterior segment sOCT provided with fan and optical distortion correction and analysis tools is an excellent instrument for evaluating and monitoring the changes produced by ICRS in keratoconic eyes. ICRS produced an improvement in the structural and optical properties of the keratoconic cornea.
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