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IOL formula eliminates guesswork, even after refractive surgery, investigators say
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PARIS — A new formula based on precise measurements of the eye allows IOL power calculation without a surgeon “fudge factor,” according to presenters here. The formula is accurate even for eyes that have undergone refractive surgery, one of the presenters said.
Paul-Rolf Preussner, of the University of Mainz, Germany, where the Okulix power calculation method was developed, said that “calibration of measurement equipment and application of transparent, exact calculation procedures make ‘individualizations’ obsolete.” He described the rationale for the technique and preliminary results here at the European Society of Cataract and Refractive Surgeons meeting.
Dr. Preussner said calculations with the Okulix formula employ several precise measurements: ray tracing of the pseudophakic eye; objective IOL data including radii, thickness and refractive index of the material, rather than the manufacturer’s “power” labeling; laser interferometry to measure axial length; and three-dimensional corneal topography to extract corneal radii. Anterior chamber depth is calculated by “a simple approach … previously calibrated in cooperation with the Vienna Eye Hospital,” he said.
According to Dr. Preussner, the mean prediction error with the Okulix formula, calculated in 65 eyes at the Mainz Eye Hospital, was “practically zero,” without any bias for long or short eyes.
Tanja M. Rabsilber, MD, of Heidelberg, described use of the Okulix formula in 12 eyes of eight patients undergoing cataract surgery after previous excimer laser refractive surgery. Corneal topography was performed with the Technomed C-Scan, and axial length was measured using the Zeiss IOLMaster.
Accuracy of prediction was calculated by comparing attempted to achieved spherical equivalent. In the 12 eyes, the mean postoperative error was less than 0.8 D, she said.
Dr. Rabsilber said Okulix is suitable and reliable to calculate IOL power for patients after excimer laser refractive surgery. She said the software is easy to use, and there is no need to know the pre-refractive-surgery biometric data — data which is often not available to the surgeon seeing the patient for age-related cataract years after refractive surgery.