IOL power calculation in post-laser refractive eyes to be easier

June 15, 2007

A new tool for pseudophakic IOL power calculation in post-laser refractive surgery eyes will help cataract surgeons provide more accurate refractive outcomes.

Key Points

Dr. Hoffer collaborated with Giacomo Savini, MD, Bologna, Italy, in creating this tool. It is a project that grew out of meetings of the IOL Power Club, an organization formed to develop new solutions for enhancing IOL power calculations and for defining guidelines from evidence-based medicine.

The tool being developed is a one-page spreadsheet that will allow entry of all the biometric data necessary for the large number of methods that have been published for estimated K readings and IOL power adjustment. It then automatically calculates those values and provides recommendations of which K reading to use and also on the most advisable IOL power.

"Everyone who does cataract surgery knows that IOL power calculation in eyes that have undergone laser vision correction is a challenge because we cannot measure the true corneal power and the index of refraction of the cornea has changed. Many methods have been proposed to overcome those problems, but the question arises of which is the right one to use. Often, the surgeon winds up falling back on the easiest approach," said Dr. Hoffer, clinical professor of ophthalmology, Jules Stein Eye Institute, UCLA School of Medicine, Los Angeles, and a private practitioner in Santa Monica, CA.

"With this spreadsheet, the surgeon still needs to know what data to collect," Dr. Hoffer said. "The spreadsheet clues you to what is needed, and after the information is entered, the program will eliminate the need for pencil and paper because it does all of the calculations automatically. In addition, by allowing all of the data collected preoperatively and postoperatively to be recorded in a single, printable sheet, it also has a potential benefit for medicolegal purposes if documentation ever becomes necessary."

Two sections

Dr. Hoffer explained that the spreadsheet is divided into two sections based on the two basic methods proposed. One section includes formulae for estimating true corneal power and the other includes methods for adjusting the target IOL power. Within each of those sections, the formulae are subcategorized further into those that require historical clinical biometric data and those that can be used with the patient's current data. It also lists aphakic refraction methods that do not require any preoperative biometric data, but depend on performing refraction in or out of the OR after the cataract is removed.