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D. A. Sediq, J. D. Edwards, K. S. Bower, L. Peppers; Corneal Biomechanics Following Epi-LASIK in US Army Personnel. Invest. Ophthalmol. Vis. Sci. 2008;49(13):648. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate variations in corneal biomechanics following epithelial laser-assisted in situ keratomileusis (Epi-lasik).
100 eyes of 50 US Army soldiers, age 21 or over underwent Epi-lasik for myopia or myopic astigmatism using the Amadeus II epikeratome and LADARVision 6000 excimer laser. Corneal biomechanics were measured using the Reichert Ocular Response Analyzer: Cornea Compensated Intraocular Pressure (IOPcc), Goldmann Correlated IOP (IOPg), Corneal Hysteresis (CH), and Corneal Resistance Factor (CRF). IOP was measured by Goldmann applanation tonometry (GAT), and central corneal thickness (CCT) by ultrasonic pachymetry. Testing was performed pre-op and at 1, 3, and 6 months post-op. Statistical analysis was performed using SPSS 15.0. A repeated measures general linear model was used to compare the IOP measurements over time; P-value < 0.05 was significant. Paired sample t-tests were used to analyze changes in CH and CRF from baseline. To adjust for 3 pair-wise comparisons, a Bonferroni correction was used and P-value <0.017 was significant.
Mean pre-op manifest spherical equivalent was -2.73D + 1.06D (range -1.13D to -6.25D). Mean ablation depth (AD) was 44.09µm + 14.24 µm. CH dropped 19.4% from pre-op at 1 month, after which it gradually increased but never fully returned to baseline. CRF decreased by 21.4% at 1 month, but unlike CH remained constant thereafter (Table 1). Stepwise regression analysis found correlations at 1 month between ΔIOPcc and ΔCCT US (R²=0.093 P= 0.005), ΔCRF and lnAD (R²=0.199 P= 0.000), at 3 months between ΔIOPcc and lnAD (R²=0.130 P= 0.002), ΔCRF and lnAD (R²=0.301 P= 0.000) and ΔCH and ΔCCT US (R²=0.60 P= 0.040) and at 6 months between ΔIOPcc and lnAD (R²=0.164 P= 0.014) and ΔCRF and ΔCCT (R²=0.185 P= 0.009).
Epi-lasik results in a significant decrease in CH, CRF, and all measures of IOP. IOPcc effectively compensates for changes following surgery. AD and change in CCT correlate most strongly with changes in CH, CRF, and IOP. Our results are consistent with previous reports on PRK and LASIK, and offer additional insights into corneal biomechanical response to advanced surface ablations.
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