Haigis and SRKT formulae accuracy for intentional myopic overcorrection

To investigate the influence of preoperative biometric parameters on the accuracy of Haigis and SRKT formulae in predicting postoperative target refraction. Retrospective analysis of 108 eyes (70 patients) underwent uneventful phacoemulsification surgery with implant of Alcon-SN60WF intraocular lens (IOL). Forty-five eyes were intentionally targeted to myopia (-0.75 to -1.25 dpt), while the others targeted between 0 and -0.75 dpt. Preoperative axial length and keratometry (K) were measured with optical biometry (LENSTAR-Haag-Streit). Postoperative spherical equivalent was assessed 3 +/- 2 months after surgery. There is a significant correlation between the mean keratometry (K) and the Haigis-SRKT prediction differences (P < 0.001; r = 0.749). Linear regression indicates that a decrease of 1 diopter (D) on K implies an increase of 0.23 D on the difference between formulae prediction. K alone does not influence the prediction error for both formulas. The difference between the two formulae is dependent on K (r = -0.75; P < 0.01). Moreover, eyes with K < 43.75 targeted at myopia (n = 23) showed a significant myopic shift of -0.26 +/- 0.09 dpt (P < 0.05) with Haigis, but a hyperopic shift of 0.24 +/- 0.09 dpt (P < 0.05) with SRKT. Divergences between Haigis and SRKT formulae cause uncertainty in choosing the IOL. Our results indicate that, in eyes with lower preoperative K, an IOL targeted at myopia might result in a small, but significant myopic shift with the Haigis formula, while a hyperopic shift with the SRKT formula.