[Toric intraocular lenses. Clinical results and rotational stability]

Correction of an astigmatism at the time of cataract surgery can be achieved in two different ways, by alteration of the corneal curvature or by implantation of a toric intraocular lens (toric IOL). In the latter, in addition to the wound architecture and IOL calculation, the influence of rotational stability in the capsular bag is most important for the refractive result.

This retrospective study included 26 eyes from 24 patients with a corneal astigmatism of 2.5-11 D before cataract surgery of which 24 eyes showed a congenital astigmatism and 2 eyes an astigmatism after keratoplasty. After phakoemulsification a three-piece toric PMMA customised IOL (6.5/13.75 mm) was implanted into the capsular bag. Subjective and objective refraction as well as keratometry and corneal topography were performed pre- and postoperatively. The axis of the toric IOL cylinder was marked and could be measured precisely in the postoperative period. The surgically induced astigmatism (SIA) was calculated.

At a mean follow-up time of 12 months after the implantation of a toric IOL, all eyes showed a reduction of total astigmatism. The mean total refractive astigmatism could be reduced from 4.16 D +/- 1.58 D preoperatively to 1.64 D +/- 1.21 D postoperatively. In 6 out of the 26 eyes (23%) the toric IOL rotated more than 10 degrees in the capsular bag and in all 6 cases the IOL rotation happened in the first 3 weeks postoperation. The IOL position was surgically corrected within 3-6 weeks after initial surgery and remained stable during the follow-up period.

The implantation of a PMMA toric IOL is a promising procedure to correct higher levels of corneal astigmatism in cataract surgery. The initial rotational stability of the haptics in the capsular bag still has to be improved and the corneal SIA has to be reduced by smaller incisions. Therefore, three-piece foldable IOLs with a new haptic design are under development.