To measure the corneal power after myopic laser in situ keratomileusis(LASIK).
Six central areas in 6 corneal power maps were studied using the OrbscanII statistical analysis device in 26 eyes that underwent myopic LASIK. Refractiveand corneal power changes were compared. Factors related to wrong cornealpower measurement were evaluated.
Main Outcome Measures
Cycloplegic refraction, refractive change at the corneal plane, andOrbscan II corneal power maps.
Preoperatively, only posterior-mean power (P<<.001)and anterior-posterior power ratio (P<<.001)varied according to the size of the analyzed area. Postoperatively, total-optical(P = .03), keratometric-mean (P = .04), total-mean (P<.001), anterior-mean(P = .03), and posterior-mean (P<<.001) powers; and anterior-posterior power ratio (P<<.001) varied according to the area. Postoperatively, the differencebetween keratometric-mean and total-mean powers became larger (P<.001), and the anterior-posterior power ratio was reduced (P<<.001). A posterior-mean power change occurred(P = .04). Refractive change after myopic LASIK wasbest estimated by 2-mm total-mean power (mean ± SD difference, 0.07± 0.62 diopters [D]; P = .55) and 4-mm total-opticalpower (mean ± SD difference, −0.08 ± 0.53 D; P = .37).
Total corneal power is more positive and refractive change is underestimatedwhen deduced from the anterior surface radius and keratometric refractiveindex. The anterior-posterior power ratio is not a fixed value. The best areato estimate the refractive change depends on the method used to obtain thepower in diopters. Refractive change tended to be underestimated in largerareas and higher preoperative myopia. Orbscan II total-mean and total-opticalpower maps accurately assess the corneal power after myopic LASIK independentof preoperative data or correcting factors, and should improve intraocularlens calculation.