Intraocular lens power calculation after radial keratotomy: estimating the refractive corneal power

Abstract

Purpose: To evaluate the most accurate method for corneal power determination in patients with previous radial keratotomy (RK).

Setting: University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA.

Methods: A retrospective review of data for 16 eyes of 14 patients with a history of RK and subsequent phacoemulsification and posterior chamber intraocular lens (IOL) implantation was performed. Outcome measures included axial length, postoperative topography, type and power of IOL implanted, and postoperative spherical equivalent (SE) refraction at 3 to 6 months. Average central corneal power (ACCP) was defined as the average of the mean powers of the central Placido rings. For each eye, simulated K-readings and different values of ACCP computed corresponding to different central corneal diameters were used in each case, along with the implanted IOL power, to back-calculate the SE refraction (Ref) via the double-K adjusted Holladay 1 IOL formula. The predicted refractive error was hence computed as (Ref - SE), both in algebraic and absolute values.

Results: The ACCP over the central 3.0 mm (ACCP(3mm)) yielded the lowest absolute predicted refractive error (0.25 +/- 0.38 diopters [D]), which was statistically lower than the error for ACCP(1mm) (P<.001) and for the simulated K-value (P = .033). It also resulted in 87.5% of eyes being within +/-0.50 D and 100% within +/-1.00 D of the actual postoperative refraction.

Conclusions: Corneal refractive power after RK was best described by averaging the topographic data of the central 3.0 mm area. Applying this method, together with a double-K IOL formula, achieved excellent IOL power predictability.