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S. Farrer, T. D. Raymond, W. Xiong, D. R. Neal, D. Baer, K. Lombardo, C. Campbell; Measurement of Post-LASIK Corneas With Full Gradient Topography. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5099.
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© ARVO (1962-2015); The Authors (2016-present)
Full Gradient Corneal Topographers (FGCT) may reveal greater topographic detail than traditional systems as they correctly capture skew rays. We compare measurements taken with a FGCT and other common corneal topographers (CT) to investigate performance differences.
Multiple CT measurements were taken with FGCT, Placido-based and Scheimpflug-image CT instruments on 64 normal and 4 post-LASIK eyes; wavefront (WF) measurements were also taken on these eyes. We compared best fit sphere (BFS), surface difference standard deviation, and elevation surface correlation.
FGCT data showed reasonable agreement to the Palcido and Sheimpflug data with the exception of the four post-LASIK corneas. The Best Fit Sphere data was well correlated between tools when these outliers were excluded from the analysis; e.g., slope=0.94 R2=0.95 compared to Placido Ring. The four outlying corneas all exhibit substantial high order aberration in both the FGCT and WF data, but not in the CT data from either other tool. In these cases, the raw full gradient topography data are similar to the tri-curve ANSI standard test surface which was developed to simulate the shape of post-LASIK eyes.
FGCT, Placido, and Scheimpflug CT measurements generally agree except in post-LASIK cases. The post-LASIK measurements showed substantial high order aberration, corroborated by WF measurements, but not captured by the conventional CT tools.
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