IOL technology focuses on implant orientation, rotation

May 1, 2008

A retrospective study of eyes with a spherical IOL implanted found the lens haptics maintained a stable position in most eyes, but significant rotation was observed in a small proportion. This information is important to consider when implanting toric IOLs where orientation and rotation can affect vision outcomes.

Baltimore-The advent of new IOL technology, particularly new toric IOLs, is accompanied by a need for surgeons to pay increased attention to implant orientation, said Robert S. Weinberg, MD, at Current Concepts in Ophthalmology. The meeting was held at Johns Hopkins University and co-sponsored by Ophthalmology Times.

This issue was the stimulus for a retrospective analysis Dr. Weinberg conducted using data from a consecutive series of eyes to characterize the postoperative rotation of a single-piece, foldable, spherical acrylic implant (SA60AT, Alcon Laboratories). Haptic location remained stable in the vast majority of the IOLs during mean follow-up of almost 18 months, according to results. Some IOLs, however, exhibited more significant rotation.

Among 100 eyes evaluated, 80% had no IOL rotation at all and in 13% of eyes, the IOL rotated less than 1 clock hour. In the remaining eyes where a greater amount of rotation was documented, vision still remained good, said Dr. Weinberg, chairman, Department of Ophthalmology, Johns Hopkins Bayview Medical Center, Baltimore.

"The main concern regarding intraoperative positioning of conventional spherical IOLs has been whether the lens was centered in the capsular bag, while little attention has been paid to haptic position," Dr. Weinberg said. "However, orientation and rotation are of critical importance, especially when implanting toric IOLs, and may be important as well for multifocal and some aspheric lenses, because they can affect the quality of vision patients achieve.

"Knowing the haptics position is important if IOL repositioning or exchange becomes necessary," he said. "Therefore, surgeons should document lens orientation at the end of the procedure after the viscoelastic has been removed."

Haptic rotation

The analysis of haptic rotation considered eyes that had not undergone Nd:YAG capsulotomy and where postoperative haptic location could be documented accurately. The evaluation compared haptic position observed at last follow-up at the slit-lamp with that recorded intraoperatively after the IOL was rotated into the capsular bag with a shaft (Sinskey Hook, Bausch & Lomb Storz). Data on the midpoint of the haptic, noted intraoperatively in terms of clock location, showed wide variation, Dr. Weinberg said.

"The aim in these surgeries was not to try to place the implant at any particular orientation, but rather, to make sure the lens rotation on implantation was sufficient to ensure the haptics were in the capsular bag and to adhere to the general rule of doing as little manipulation as possible," he explained.

"One potential criticism of this study is that the intraoperative position of the haptics was noted before the viscoelastic was removed and before acetylcholine was instilled," he said. "Both of these steps may result in some implant rotation."

Dr. Weinberg added that irrigating under the IOL particularly may affect implant orientation.

"I don't irrigate under the IOL to remove viscoelastic, but I did use that technique in one case in this series," he said.

"This particular eye exhibited the greatest amount of rotation, 3 clock hours."

Commenting on the results, Dr. Weinberg suggested that small amounts of rotation might reflect the sensitivity of the assessment technique; haptic position was based on visual observation through the surgical microscope or slit-lamp without use of any special instruments. Cyclotorsion also may play a role considering that the intraoperative assessment was made with the patient in the supine position on the operating table and the postoperative evaluation was recorded with the patient sitting upright at the slit lamp.

"We know from our experience with LASIK that cyclotorsion of the eye occurs between the supine and upright position, and that may account for the appearance of up to 1 clock hour of rotation," Dr. Weinberg said.

Analyses to determine factors predicting greater rotation showed that the eyes with more than 1 clock hour rotation only differed significantly from the overall population by having a longer mean duration of follow-up.

"Particularly in older patients, capsular bag contraction occurs over time and may affect IOL orientation," he concluded.OT