EyeWorld India September 2018 Issue

higher preoperative astigmatism,” Dr. Lee explained. “Furthermore, about half of the patients in each group had the lowest power toric IOL, which corrects 1 D of cylin- der at the corneal plane. In those eyes, the refractive effect of a ro- tated IOL would be more limited. These factors might have canceled out the fact that the AcrySof toric is 10% less likely to rotate more than 5 degrees. “The problem was not the mean difference in IOL stability, which was statistically significant but small (1 degree in favor of AcrySof),” Dr. Lee continued. “It was the number of large rotations in the Tecnis group—these are the patients who are unhappy because of their poor refractive outcomes.” “Overall, we would conclude that both toric IOL models provide excellent refractive outcomes and good rotational stability. However, the large size of our study made it apparent that the AcrySof had superior rotational stability,” Dr. Chang added. This is the largest study to date that directly compares rotational stability of these two toric IOLs. What’s more, Dr. Lee said it was important to look at rotational stability at the first postoperative visit. “The FDA studies for toric IOL approval looked at stability after the first postoperative visit. How- ever, we thought, based on clinical experience, that rotations happen before that,” Dr. Lee said. “The 2017 report by Inoue et al. that we reference eventually confirmed that, as they showed that 85% of their rotation happened in the first hour after surgery.” 3 Dr. Chang added that 28% of the net mean toric IOL misalignment measured at 1 year in the Inoue study, where patients were manually marked preoperatively, was due to surgical misalignment. “This means prior studies of toric IOL misalignment using manual marking were un- able to differentiate between surgi- cal misalignment and postop IOL rotation,” he said. “By using intra- operative digital alignment with Callisto in all eyes, we were able to isolate postoperative IOL rotation as a variable when comparing the two different toric IOLs.” Dr. Chang observes intraopera- tively that there is more stiffness to the Tecnis IOL haptic and its optic-haptic junction, which he thinks could increase the likeli- hood of it rotating when compres- sive forces are applied to it. “The reduced compression force of the AcrySof toric haptic, which is floppier, probably allows it to absorb any pressure applied to the IOL by more readily flexing,” Dr. Chang said. “Imagine equato- rial point pressure applied to the haptic midway between its tip and the optic junction. If it were limp, like a noodle, the haptic would simply flex. If it were stiffer and rigid, the force would be transmit- ted to the entire lens, and it might tend to turn counterclockwise as the pressure follows the natural curve of the haptic.” Why do IOLs seem to rotate so early in the postop period? Dr. Lee speculated that the haptics might be continuing to expand in some cases, or perhaps leakage of the wound or retained viscoelas- tic around the haptics could be a factor. “It takes a while for the cap- sular bag to shrink and collapse around the IOL,” Dr. Chang said. “Anecdotally, I think it helps to leave the eye slightly hypotonous at the conclusion of surgery. Inflat- ing the eye with balanced salt solution tends to simultaneously expand the capsular bag.” As a result of this study’s find- ings, Dr. Lee said he prefers to use the AcrySof as his usual monofocal toric IOL. Though toric IOL reposi- tioning is straightforward, he said the associated inconvenience, the Despite ensuring correct axis alignment con rmed with a digital marking system, this study showed IOL rotation was possible within postop day 1. This image shows a Tecnis toric IOL with the Callisto overlay. Source: David F. Chang, MD cost of a return to the OR, and the theoretical risk for infection or zonular damage have him trying to avoid the need altogether. The IOLs that they did have to rotate in the study period, how- ever, were stable afterward, Dr. Lee noted. “I think the take-home message is that if you have an IOL rotation, wait a couple of weeks, then fix it because your patient will be much better off,” Dr. Lee said. Dr. Chang said he prefers the AcrySof as a monofocal toric op- tion, but he also implants many Symfony and Symfony toric IOLs. If the first eye develops 10 degrees or more of misalignment, he’ll reposition it simultaneously with cataract surgery in the second eye. He’ll then use a capsular tension ring (CTR) with the Symfony toric in the second eye. He said he might also use a CTR if the patient has high axial myopia or conditions that would make repositioning Head-to-head – from page 33 34 EWAP CATARACT/IOL September 2018