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M. S. Raam, F. W. Medeiros, A. Sinha Roy, K. M. Hallahan, W. J. Dupps, Jr.; Comparison of Ocular Response Analyzer (ORA) Waveform Changes in Myopic vs. Hyperopic LASIK. Invest. Ophthalmol. Vis. Sci. 2009;50(13):902.
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© ARVO (1962-2015); The Authors (2016-present)
To compare changes in Ocular Response Analyzer (ORA, Reichert, Inc.) standard and waveform-derived variables in patients undergoing myopic and hyperopic LASIK refractive surgery.
Pre-operative and 1 week post-operative ORA measurements from 26 eyes of 13 myopic subjects and 22 eyes of 11 hyperopic subjects, all of whom underwent femtosecond-assisted LASIK refractive surgery, were studied retrospectively. Changes in two standard and thirteen waveform-derived ORA variables between these two time points were compared between myopic and hyperopic groups. The standard variables are given by the Reichert ORA device software (version 1.01), while the waveform-derived variables, which we previously presented at ARVO 2008, were computed from various mathematical features of the raw pressure and infrared signal waveforms using MATLAB R2008a (The MathWorks, Inc.), as described in the figure.
Mean pre-to-post-operative changes in the myopic group and in the hyperopic group are displayed in the figure, as well as the results of testing the null hypotheses that the change in each variable is equal in both groups. Changes in five of the waveform-derived variables – ConcavityTimeNormalized, MeanTroughNormalized, MinAOnsetRatio, HysteresisLoopArea, and Pmax – were more pronounced in myopes than in hyperopes. Changes were also more pronounced in myopes than in hyperopes for both of the standard variables: corneal hysteresis (CH) and corneal resistance factor (CRF).
Our study demonstrates that eight of the thirteen waveform-derived ORA variables were impacted by both myopic and hyperopic LASIK. Moreover, five of the waveform-derived variables and both of the standard ORA variables, CH and CRF, were differentially affected by myopic and hyperopic LASIK and may reflect fundamental differences in myopic and hyperopic ablation profiles, as well as their biomechanical impact on the central cornea.
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