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Pete S. Kollbaum, Ryan McGiffen, Jayoung Nam; Generalized Surface Models of Keratoconic Corneal Shape. Invest. Ophthalmol. Vis. Sci. 2012;53(14):120.
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The aim of the current study was to determine simple generalized surfaces, which could be used to describe keratoconic corneal shape. These shapes may be useful in contact lens design to provide improved fit or optics.
Retrospective Orbscan maps were obtained from 108 eyes with a clinical diagnosis of keratoconus (KCN), 71 eyes which did not have a clinical diagnosis but the fellow eye did (KCF), 64 suspect eyes (KCS) and 67 normal eyes with no evidence of any corneal disease (NRM). Custom MATLAB software was used to obtain and analyze the instrument raw axial and elevation data. Six different rotationally, and non-rotationally symmetric methods with increasing number of parameters were used to find the optimal apical radius (r, mm) and conic constant (k) for each map.
All methods demonstrated the poorest fit to KCN eyes, but with mean errors under 0.07 microns RMS for fits to elevation. Different fitting methods yielded different parameter estimates. For the general conic fit to elevation, KCN eyes had an ave±std r of 7.0±0.7mm and k of -0.5±0.6, while NRM eyes had a flatter and less variable r (7.6±0.5mm) and k (-0.2±0.3mm).
Different methods of determining surface parameters yield slightly different results. A wider distribution of surface shape parameters with steeper apical radii and conic constants is needed to describe diseased corneal shape, and two parameter models may be insufficient for highly irregular eyes.
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