comparison of different methods for intraocular lens power calculation after corneal refractive surgery

with the increasing number of keratorefractive surgical procedures in the past years, an increasing number of cataract operations in eyes with previous keratorefractive surgery is anticipated. although cataract extraction seems to be feasible without major technical obstacles, intraocular lens (iol) power calculation remains problematic. insertion of measured k-readings after myopic photorefractive keratectomy (prk), or laser in situ keratomileusis (lasik) into standard iol power-predictive formulas commonly results in substantial under correction and postoperative hyperopic refraction or anisometropia. several methods have been developed to provide accurate measurements of corneal power which include: clinical history method, contact lens method, feiz-mannis formula, aphakic refraction technique, cornea bypass method and the besst formula. newer methods such as the besst formula represent a significant step toward greater accuracy in iol power calculation in eyes with previous laser refractive surgery, especially when prerefractive surgery data is unavailable. the “clinical history method” should be applied whenever refraction and k-reading before the keratorefractive procedure are available, however if the pre- refractive surgery data is unknown, the use of the flattest k value in the central 3 mm region of the topography map will be useful. this article briefly reviews each of the above-mentioned methods.