IOL Power Calculation in Patients with Previous RK

To report the results of different methods for true corneal power and intraocular lens (IOL) power calculation in 10 eyes with previous radial keratotomy (RK) with or without astigmatic keratotomy. In this case series including 10 eyes of 7 patients who had undergone RK with or without astigmatic keratotomy, we firstly determined corneal power using two contact lens method (CLM) and mean keratometry of 3 mm zone in topography. In the next step, IOL power of these eyes was calculated using three formulas including SRK II, SRK T and Holladay II, but the results of Holladay II formula were used as determinant of IOL power during cataract surgery. Since 1.50 diopter change in IOL power results in 1.00 diopter change in patient’s refraction at spectacles plane, we estimated the manifest refraction of these eyes with other formulas for comparing with the results of Holladay II formula three months after cataract surgery. Postoperative manifest refraction in 8 eyes by using CLM ranged from -3.00 to +2.00 diopter. In both CLM and mean keratometry of 3 mm zone in topography, the amount of hyperopia after cataract surgery with SRK II formula was more than SRK T, and with SRK T was more than Holladay II. Mean spherical equivalent was 0.08 diopter in mean keratometry of 3 mm zone in topography and Holladay II formula and -0.05 diopter in CLM and Holladay II formula indicating adequate precision of these two methods. It seems that after RK, mean keratometry of 3 mm zone in topography yield a precise estimate of true corneal power as compared to CLM and that Holladay II formula has the most exact result closer to emetropia in comparison with SRK II and SRK T formulas.