New factor to improve reliability of the clinical history method for intraocular lens power calculation after refractive surgery

PURPOSE: To determine whether the refractive error in an eye developing cataract after refractive surgery represents actual regression or is cataract related and whether the method to gather this information would allow the use of history-related formulas in intraocular lens (IOL) power calculation after refractive surgery. SETTING: Second University of Naples, Naples, Italy. DESIGN: Case series. METHODS: The refractive effects, axial length (AL), and mean keratotomy (K) values were evaluated in eyes before and 6 months after photorefractive keratectomy for myopia or for myopic or mixed astigmatism. RESULTS: The study evaluated 257 eyes of 166 patients (93 women). Before surgery, there was a high correlation between refractive error and the product of AL and K (AL x K) (r(2) = 0.8213). In patients with refractive results close to emmetropia, the mean AL x K was 1005.91 +/- 25.88 (SD), meaning that in the range of 954 and 1058, there was a 95% possibility that the patients were almost fully corrected. The following regression formula was obtained to calculate the amount of refractive error independent of cataract onset: Refractive error = -0.0157 x (AL x K) + 16.437. CONCLUSIONS: The regression formula determined whether the refraction depended on the onset of cataract and estimated the amount of undercorrection or overcorrection that occurred after refractive surgery, leading to improved estimation of the power of the IOL to be implanted. It may allow the use of history-related formulas in IOL power calculation for eyes that have had corneal refractive surgery.