Calculation of the precise lens power in patients that have had prior refractive surgery presents a new set of challenges. All the current standard formulas are based on native corneas. They use the front surface curvature to "assume" a position for the implant inside of the eye at the time of cataract surgery. The problem with such assumption is that in cases of patients that have had prior refractive surgery such as RK, PRK, or LASIK, the corneal surface curvature has been altered, yet the lens implant at the time of the cataract surgery will behave similar to what the native eye would have done.

The American Society of Cataract and Refractive Surgery (ASCRS) has recognized such challenge and created a calculator to help all surgeons (regardless of membership) for free. The calculator can be reached at http://iol.ascrs.org/

In the ASCRS's calculator, Post-LASIK/PRK data has fields of input from the ATLAS Corneal Topographer (Carl Zeiss Meditec, Dublin, CA). The input fields are the 0, 1, 2, and the 3 mm rings.

For the ATLAS Models 991, 993, and 995 on can simply choose the "Numerical View" page to acquire such data.

In the ATLAS 9000 Model, when in the "Axial Curvature Map" view, choose "More (F2)" from the bottom left hand corner. That will open more options. There are 4 tabs on top and the last tab is "Data." Under the Data tab, there is a section called "Averages." Choose the ring option and the check boxes next to 0 mm, 1 mm, 2 mm, and the 3 mm. This will display the data on the screen for use in the IOL Calculator.