November 2007




Post-Refractive Surgery IOL Calculator on ASCRS Web Site

by John Ciccone ASCRS Director of Communications


IOL CalculatorThe Post-Refractive Surgery IOL Calculator is now available on the ASCRS Web site at The program is free to use by members and non-members alike. Tools for three types of calculations are available: prior myopic LASIK IOL calculations, prior hyperopic LASIK IOL calculations, and prior RK calculations.

The program was developed by a generous unrestricted $9,000 grant from Alcon Laboratories of Fort Worth, Texas through the ASCRS Foundation. We’re encountering a growing number of patients who have undergone laser refractive surgery and those who have had radial keratotomy. The importance of this program is that it puts in one place, many, if not most of the best formulas for calculating the IOL power in these difficult cases, said Douglas Koch, M.D., of the Baylor College of Medicine. The idea for the calculator began with a March, 2006 editorial in the Journal of Cataract and Refractive Surgery, written by then editor, Douglas Koch, which noted the list of ways to calculate intraocular lens power in eyes that have had photorefractive keratectomy (PRK), or LASIK was long and growing. “Ideally, it would be optimal to have a spreadsheet that allows the clinician to insert all values available. The various formulas would then be calculated automatically.”

After reading the editorial, Warren Hill, M.D., Mesa, Arizona, who had already developed such spread sheets, contacted Dr. Koch and the collaboration began with the assistance of Li Wang, M.D., department of ophthalmology research associate at the Baylor College of Medicine in Houston, Texas, and her husband Jianzhong Ma. “They did the heavy lifting for the calculator’s coding and elements of its design,” Dr. Hill noted. Whatever data you can accumulate, you can enter into a spread sheet and it calculates the IOL power with the formulas that can be used based on the data that you enter. This maximizes the number of formulas you can use with the data you have available at the time. It saves time, it eliminates calculation errors, and, based on the way data is entered, it eliminates formula errors, Hill said “When using the program, people need to adhere strictly to the type of data they use as inputs,” said Dr. Hill. When the program asks for a specific methodology, such as IOLMaster or the Leica Zeiss Humphrey Atlas topographer ( both by Carl Zeiss Meditec, Dublin, Calif./Jena, Germany), etc., they need to pay attention to exactly what the calculator is asking for. If they enter information from another instrument, it may not work, he added.

Similarly, Hill said, if they wish to use the Hagis L feature of the calculator, they need to know their Hagis constants. The calculator will give them as many different methodologies as there is information supplied by the user, Hill said. For the myopic LASIK calculator, the program is set up in three columns. One set of methodologies is using the pre-LASIK keratometry and the change in manifest refraction. So, all of those methods that have that as their fundamental mathematical basis will be in that column. There are four methodologies that just use the change in manifest refraction, and then there is one column that uses only objective information from the cornea being directly measured by certain instruments. It is nice to be able to compare the columns of data side by side, when they all line-up, the user is on a very solid footing. When there is a big discrepancy between one class of calculations and another, it means that one part of the mathematical puzzle is either incorrect or it is missing.


John Ciccone is director of communications for the American Society of Cataract and Refractive Surgery. Contact him at 703-591-2220.

Post-Refractive Surgery IOL Calculator Post-Refractive Surgery IOL Calculator
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