Comparison of different formulas for calculating intra-ocular lens (IOL) power after excimer laser kerato-refractive surgery for myopia.

In this retrospective case study, the results of 29 eyes with cataract and history of myopic laser refractive surgery (PRK or LASIK) are presented. The IOL power calculation were done based on the myopic Haigis-L formula provided with the IOLMaster 700, and all or some of the formulas presented on the website of the American Society of Cataract and Refractive Surgery (ASCRS IOL Calculator) depending on the equipment available (Wang- Koch-Maloney, Shammas, Haigis-L, OCT-based, Galilei-based, Potvin-Hill Pentacam, Barrett True K, and average, minimum and maximum of all given formulas). Regarding the implanted IOL power and the obtained refraction (spherical equivalent) at least one month for each case after Phaco emulsification cataract surgery, the optimal IOL power and its difference with the proposed power of each of the formulas were determined.

The mean powers of implanted IOL and optimal IOL in all eyes were 20.63±4.53 and 18.75±4.82 diopters, respectively. The lowest and highest calculated IOL powers were based on the Potvin-Hill Pentacam and the Haigis-L formulas, respectively. The least difference between the optimal IOL power and the used formulas were related to the Wang-Koch-Maloney method and the average of all formulas of ASCRS IOL Calculator, while the highest difference was seen with the Haigis-L formula.

Lack of access to the pre-operative refractive and keratometric data present the surgeon with a major problem in calculating IOL power after corneal excimer laser refractive surgery and sometimes creates unexpected results and refractive surprises.