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Steven M. Christiansen, Majid Moshirfar; Comparison of the Ratio of Keratometric Change to Refractive Change Induced by Myopic Ablation. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1492.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the ratio of keratometric change (ΔK) to refractive change (ΔSE) induced by refractive laser ablation and to propose an equation to predict the postoperative K prior to surgery.
The charts of 2738 eyes were reviewed of patients that underwent laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) between March 2007 and March 2010. One-thousand and twenty eyes with ΔSE of 0 to 2.99 D (Low ΔSE) were compared with 1253 eyes with ΔSE of 3.00 to 5.99 D (Moderate ΔSE) and with 465 eyes with ΔSE greater than 6.00 diopters (High ΔSE). Statistical analysis was performed using an independent student t-test of equal variance and a best-fit equation was produced from all ΔK/ΔSE data.
Significant differences were found in the ratio ΔK/ΔSE between eyes with Low ΔSE vs. Moderate ΔSE (0.98 ± 0.60 vs. 0.80 ± 0.17, p=1.02 x 10-25), Moderate ΔSE vs. High ΔSE (0.80 ± 0.17 vs. 0.77 ± 0.11, p=1.01 x 10-14), and Low ΔSE vs. High ΔSE groups respectively (0.98 ± 0.60 vs. 0.77 ± 0.11, p=4.55 x10-4). The equation that best predicts the postoperative K prior to surgery was found to be K=x-(y*z), where x=preoperative K, y = -0.264*ln(attempted ΔSE) + 1.1788, and z=attempted ΔSE.
The change in simulated K required to achieve a diopter of myopic refractive correction decreases as the amount of refractive change increases, is more variable with lower amounts of correction, more constant with higher amounts of correction, and follows a non-linear relationship.
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