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Aspheric IOL shows stable centration, minimal rotation at 6 months postop
J Cataract Refract Surg. 2010;36(9):1523-1528.
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An aspheric IOL proved stable and showed potential suitability for the addition of a toric surface to correct corneal astigmatism, a study showed.
"Although the IOL did not have a toric optic, we do not believe the change in thickness profile when toricity is added would have a significant effect on rotational stability or centration," the study authors said.
The authors stressed the role of accurate centration with no rotation in contributing to the refractive outcomes of toric IOLs.
"There is a sinusoidal relationship between the amount of axis misalignment and the residual cylinder power," they said. "Therefore, small misalignments cause disproportionately larger losses of cylindrical effect. If a cylindrical correction rotates 30 degrees off-axis after surgery, there will be no correction of the astigmatic power, although the resultant cylinder will have shifted to a new axis."
The multicenter study included 107 patients who underwent phacoemulsification and monocular implantation of an Akreos AO aspheric IOL (Bausch + Lomb). Mean patient age was 69.9 years.
IOLs were imprinted with conjunctival orientation marks before surgery to provide reference points for IOL alignment. The authors used slit lamp biomicroscopy with 10-times magnification and retroillumination to assess IOL centration and rotation.
Investigators imaged IOLs postoperatively at 1 to 2 days, 7 to 14 days, 30 to 60 days and 120 to 180 days. IOL rotation was assessed in 97 eyes; centration was assessed in 76 eyes.
Study data showed a mean rotation of 1.93° between the first day after surgery and the 120- to 180-day interval; 96% of IOLs rotated less than 5°, and 99% rotated less than 10°.
IOL centration changed a mean 0.21 mm between day 1 and the 120- to 180-day follow-up. All IOLs were off centration by less than 0.5 mm, the authors said.
"There was no significant decentration between visits and no clear bias in the direction of the decentration," they said. "The Akreos AO IOL platform should provide excellent rotational and centration stability with which to correct corneal astigmatism through the application of a toric optical surface."