Objective: To evaluate the accuracy of computerized videokeratography, keratometry, and the Gaussian optics formula for measuring corneal refractive power in patients after myopic laser in situ keratomileusis (LASIK).
Design: Noncomparative case series.
Participants: One hundred eyes of 63 patients (mean age, 45.0 +/- 10.9 [standard deviation] years) who underwent LASIK were included in the study.
Methods: Using the clinical history method as the standard, we evaluated the accuracy of values of corneal refractive power derived from computerized videokeratography (the EffRP value of the EyeSys Corneal Analysis System, which averages corneal refractive power over the central 3 mm), keratometry (K), the Gaussian optics formula (GauRP), and values of EffRP and keratometry as modified according to the amount of LASIK-induced refractive change.
Main Outcome Measures: Correlation of measured corneal power values to those obtained using clinical history method (HisRP).
Results: Although the values for HisRP were significantly correlated with postoperative EffRP and K values and with GauRP, postoperative EffRP and K values were higher than HisRP (0.87 +/- 0.68 diopters [D] and 1.16 +/- 1.10 D, respectively), and GauRP were lower than HisRP (0.44 +/- 0.66 D) (P < 0.001 for all three comparisons). The differences between HisRP and both postoperative EffRP and K values increased significantly with the amount of myopic correction. The most accurate results were obtained by modifying the postoperative values of EffRP according to the amount of LASIK-induced refractive change; 70% of these values were within +/- 0.5 D and 94% within +/- 1 D of HisRP values.
Conclusions: Using the clinical history method as the standard, we found that the most accurate method for determining corneal refractive power in post-LASIK eyes was to adjust the postoperative corneal measurement according to the amount of LASIK-induced refractive change.
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