Purpose : To compare results of different methods for true corneal power determination and intraocular lens (IOL) power calculation formulas in 10 eyes of 7 patients with previous radial keratotomy (RK) with or without astigmatic keratotomy

Methods : In this case series study, we determined the corneal power of 10 eyes of 7 patients who had undergone RK with or without astigmatic keratotomy with two methods: the contact lens method (CLM) and the mean keratometry of the 3 mm zone in topography. In the next step, the IOL power for these eyes was calculated with the 3 formulas of SRK II, SRK T, and Holladay II the latter was used for the IOL selection. Refractive results were determined 3 month after surgery. According to the rule that 1.5 diopter (D) change in IOL power results in 1.0 D change in a patient’s refraction at the spectacle plane, we estimated the manifest refraction of these eyes with other formulas and compared them with the results achieved by Holladay II formula.

Results : Using the CLM and Holladay II formula, the postoperative manifest refraction spherical equivalent in 8 eyes ranged from -3.00 to +2.00 D. Both CLM and the mean keratometry of the 3 mm zone in topography lead to a greater degree of hyperopia after cataract surgery with SRK II formula than SRK T, and with SRK T than Holladay II. The mean spherical equivalent with mean keratometry of the 3 mm zone in topography and Holladay II formula was 0.08 D, and with CLM and Holladay II formula was -0.05 D.

Conclusion : In this study, it seemed that after RK, the mean keratometry of the 3 mm zone in topography gives a better estimate of true corneal power compared with CLM, and that the Holladay II formula brings results closer to emetropia compared with SRK II and SRK T formulas.