Square posterior optic edge design reduces PCO risk

Using a rabbit model, Dr. Apple evaluated the development of PCO after implantation of the AR40e and three other hydrophobic acrylic IOLs. The comparator lenses were all AcrySof (Alcon Laboratories) models and included the three-piece MA60AC, the one-piece SA30AT, and the one-piece SA60AT. The AcrySof IOLs have square anterior and posterior edges. The OptiEdge of the AR40e is characterized by a round anterior edge, a sloping side edge, and a square posterior edge.

Each IOL model was implanted in eight eyes by a single surgeon (Nick Mamalis, MD). The surgeries were all performed in a single day, and the animals were killed after 3 weeks. Miyake-Apple views were used to assess central and peripheral PCO as well as IOL centration, haptic fixation, and the intensity of Soemmering's ring.

"The sample sizes in this study were too small to establish any statistically significant differences," Dr. Apple said.

"However, they certainly show clear trends of the benefit of a square posterior edge for reducing PCO because the performance of the AR40e is markedly improved relative to what we found in similar earlier studies evaluating the AR40 model, which features round anterior and posterior edges."

Through a series of laboratory studies he performed during the mid- to late 1990s, Dr. Apple identified six factors-three IOL-related and three surgery-related-that are important for reducing PCO. A square posterior edge optic, use of a biocompatible IOL material, and maximal IOL optic-posterior capsule contact were identified as the three IOL-related factors.

"Those features had been defined based on the performance of the AcrySof IOL, which 5 to 7 years ago was clearly superior to other implants with respect to PCO prevention. Manufacturer modifications in IOL design based on information gained in the elucidation of these PCO prevention factors have been valuable for greatly reducing the development of PCO," Dr. Apple said.

Importance of haptic design He observed that his previous studies also pointed to the importance of haptic design in PCO prevention secondary to its effect on positioning the IOL optic against the posterior capsule. In addition, it is a determinant of long-term, in-the-bag IOL fixation.

Results from evaluations of IOL centration and haptic fixation in the rabbit study also demonstrated favorable performance of the AR40e IOL.

Seven (87.5%) of eight AR40e IOLs remained centered, compared with six (75%) SA30AT IOLs, six (75%) SA60AT IOLs, and five (62.5%) MA60AC IOLs. Comparisons between IOL groups based on mean IOL decentration measured in millimeters showed no statistically significant differences.

When surgery was completed, both haptics appeared to be in the bag in all eyes. Three weeks later, both haptics remained in the bag in seven (87.5%) eyes with the AR40e IOL implanted, six (75%) of each of the eight eyes with the MA60AC and SA60AT IOLs implanted, and in four (50%) recipients of the SA30AT IOL.

"For all IOL groups, PCO scores were lower among the subgroup with both haptics fixated in-the-bag compared with the entire group of eight lenses. The fact that more AR40e IOLs had both haptics in the bag may have contributed to its lowest PCO scores," Dr. Apple noted.