Reliability of the IOLMaster in Measuring Corneal Power Changes After Hyperopic Photorefractive Keratectomy

Abstract

PURPOSE: To test the accuracy of the IOLMaster (Carl Zeiss Meditec) in detecting corneal power changes after hyperopic photorefractive keratectomy (PRK). METHODS: Forty-five consecutive eyes that underwent hyperopic PRK with the SCHWIND ESIRIS excimer laser, ranging from +0.75 to +7.00 diopters (D) (mean: +3.84±1.56 D), were analyzed. Data included pre- and postoperative (1, 3, and 6 months) fogging refraction and automated keratometry (K). Statistical analysis was performed to determine the correlation between the changes in refraction at the corneal plane and the changes in keratometry. RESULTS: The mean difference between the changes in refraction and the measured corneal changes was +0.27±1.19 D (range: -1.91 to +4.28 D) (P=.18) at 1 month; +0.56±0.97 D (range: -1.00 to +2.96 D) (P=.006) at 3 months; and +0.67±0.80 D (range: -0.73 to +2.31 D) (P=.00002) at 6 months. Based on these results, we suggest using the regression formula found at 6-month follow-up (y=0.8074 x + 0.092) to better calculate the effective corneal power. Comparison between the data obtained with IOLMaster measurements and equivalent K readings from the Holladay report obtained with the Pentacam (Oculus Optikgeräte GmbH) shows good agreement (R(2)=0.9). CONCLUSIONS: Automated keratometry provided by the IOLMaster underestimates the effective refractive changes after hyperopic PRK, and a correcting factor is needed to calculate the corneal power in these cases.