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Siamak Zarei-Ghanavati, Arturo Ramirez-Miranda, D. Rex Hamilton; Corneal Biomechanical Properties In Keratoconic Versus Post Femtosecond-Assisted LASIK Eyes After Statistical Correction For Potentially Confounding Factors. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5177.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate and compare the corneal biomechanical waveform parameters between keratoconic (KCN) and post femtosecond laser in situ keratomileusis (FLASIK) eyes after controlling for potentially confounding factors
The Ocular Response Analyzer (ORA, Reichert Instruments) was used to obtain the corneal hysteresis (CH), corneal resistance factor (CRF) and 37 other biomechanical waveform parameters from 105 manifest keratoconic eyes and 94 post-FLASIK eyes. A multivariate logistic regression model and Spearman correlation coefficients were used to evaluate the linear best-fit relationship between variables. After controlling for central corneal thickness (CCT) and age, the model was used to select those parameters which were most useful in distinguishing between the KCN and post FLASIK groups.
The mean CH and CRF were 8.2±1.5 SD mmHg (range, 6.5-11.6) and 7.5±1.8 SD mm Hg (range, 5.1-11.0) in keratoconic eyes compared with 9.2±1.2 mmHg (range, 6.7-12.3) and 8.1±1.4 SD mm Hg (range, 5.2-12.0) in post FLASIK eyes, respectively. The differences were statistically significant for both CH and CRF (p<0.0001and p=0.006, respectively). After statistically controlling for differences in CCT and age, differences between the mean of the following waveform parameters were found to be statistically significant: CH (p=0.003), HFN (high frequency "noise" in the region between ORA peaks, p<0.0001), WP2 (width of the ORA second peak at "base", p=0.003), DSP1 (down-slope of the first peak of ORA wave, p=0.0001), a-index (degree of "non-monotonicity" of rising and falling edges of the first peak of ORA wave, p=0.0004), USP1 (upslope of the first peak of ORA wave, p=0.0007), and AP1 (area under the first peak of ORA wave, p=0.042). The area under the receiver operator characteristic (ROC) curve for the model using these parameters was 0.932.
We found a statistically significant difference in the mean CH but not in the mean CRF between keratoconic and post-FLASIK eyes after controlling for age and CCT. Differences in multiple other ORA waveform parameters between the 2 groups suggest that the corneal biomechanics are quite different between KCN from post-FLASIK corneas. Future studies should focus on determining the clinical significance of these alternative waveform parameters.
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