Intraocular lens power calculation after radial keratotomy: Estimating the refractive corneal power
Accepted 2 March 2007.
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 (ACCP3mm) yielded the lowest absolute predicted refractive error (0.25 ± 0.38 diopters [D]), which was statistically lower than the error for ACCP1mm (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.
From the Department of Ophthalmology (Awwad, Dwarakanathan, Bowman, Cavanagh, Verity, Mootha, McCulley), University of Texas Southwestern Medical Center, Dallas, Texas, USA; Department of Ophthalmology (Awwad), American University of Beirut Medical Center, Beirut, Lebanon
Corresponding author: James P. McCulley, MD, Department of Ophthalmology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9057, USA.
James. P. McCulley, MD is a consultant to Alcon Laboratories. No author has a financial or proprietary interest in any material or method mentioned.
Supported in part by an unrestricted grant from Research to Prevent Blindness, New York, New York, USA.
ABSTRACT