Eyeworld

EW CATARACT 24 May 2018 by Liz Hillman EyeWorld Senior Staff Writer 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 unable to differentiate between surgical misalignment and postop IOL rotation," he said. "By using intraoperative digital align- ment 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 intraoper- atively that there is more stiffness to the Tecnis IOL haptic and its op- tic-haptic junction, which he thinks could increase the likelihood of it rotating when compressive forces are applied to it. "The reduced compression force of the AcrySof toric haptic, which is more floppy, probably allows it to absorb any pressure applied to the IOL by more readily flexing," Dr. Chang said. "Imagine equatorial 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 transmitted to the entire lens, and it might tend to turn counterclockwise as the pres- sure 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 viscoelastic around the haptics could be a factor. "It takes awhile for the capsular bag to shrink and collapse around the IOL," Dr. Chang said. "Anecdot- ally, I think it helps to leave the eye slightly hypotonous at the conclu- sion of surgery. Inflating the eye with balanced salt solution tends to simultaneously expand the capsular bag." As a result of this study's findings, Dr. Lee said he prefers to use the AcrySof as his usual mono- focal toric IOL. Though toric IOL repositioning is straightforward, he said the associated inconvenience, statistical significance (P=0.1), more patients with the Tecnis lens under- went IOL repositioning compared to the AcrySof (3.1% v. 1.6%). Though Tecnis lenses were more likely to rotate by the first postop visit, the net mean refractive out- comes between the two groups were similar. "Although the groups were similar demographically, the Acry- Sof group had significantly 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 cylinder at the corne- al plane. In those eyes, the refractive effect of a rotated 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 num- ber 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 supe- rior 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 im- portant 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. However, we thought, based on clinical experi- ence, 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 mis- alignment measured at 1 year in the Dr. Lee and Dr. Chang com- pared the axis alignment of the Tecnis toric monofocal IOL (John- son & Johnson Vision, Santa Ana, California) and the AcrySof toric monofocal (Alcon, Fort Worth, Texas) at the first postoperative visit (either day 0 or day 1). The lenses were implanted at a single ambu- latory surgery center by the two surgeons using intraoperative wave- front aberrometry (ORA VerifEye+, Alcon) and the Callisto Eye digital marking system (Carl Zeiss Meditec, Jena, Germany). Dr. Chang said he and Dr. Lee were not aware of any head-to-head studies evaluating postoperative rotational stability— an important factor in overall toric IOL performance—between these two platforms. Six hundred and forty-sev- en Tecnis lenses and 626 AcrySof lenses were implanted during the 18-month study period. Overall, the AcrySof lens showed statistical- ly better rotational stability when compared to the Tecnis lens. More specifically, the AcrySof lens rotated <5 degrees in 91.9% of eyes, com- pared to 81.8% with the Tecnis lens (P<0.0001), and <10 degrees in 97.8% of eyes compared to 93.2% with the Tecnis (P=0.0002). The net mean rotation of the AcrySof lens was 2.72 degrees, compared to 3.79 degrees with the Tecnis (P<0.05). Though it did not quite reach Tecnis monofocal toric lens found to rotate more than AcrySof toric lens S table alignment of toric IOLs is critical for achiev- ing a desired refractive outcome. Just 1 degree of misalignment results in about 3.5% loss of cylindrical cor- rection, 2 degrees up to about 7%, and 10 degrees more than 34%. 1 Even if the surgeon aligned the IOL on the proper axis, postoper- ative rotation can and does occur, impacting refractive results. In a study published in Ophthalmology, David F. Chang, MD, clinical pro- fessor of ophthalmology, University of California, San Francisco, and Altos Eye Physicians, Los Altos, Cal- ifornia, and Bryan S. Lee, MD, JD, in private practice with Dr. Chang at Altos Eye Physicians, Los Altos, sought to compare the postoperative rotational stability of the two most commonly implanted toric monofo- cal IOLs. 2 "Toric IOLs are the most com- mon premium IOL in our practice," Dr. Lee said. "We integrated intraop- erative aberrometry, then a digital marking system to increase the accuracy of our toric IOL placement, so it was natural for us to study the next step—whether the IOL stays where we put it." Head-to-head comparison of toric IOLs shows one significantly more likely to rotate by postop day 1 Despite ensuring correct axis alignment, confirmed 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

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