Astigmatic correcting IOL

Rotational stability can be attributed to both bio-mechanical as well as bio-material properties as it involves lens capsular dynamics. In the case of the Tecnis 1-piece IOL the bio-mechanical stability advantage is due to the 3 points of contact to the lens capsule referred to as the 'tri-fix' design with the 2 haptics and the posterior surface of the optic due to the posterior off-set or step vaulting between the optic and the haptics. The bio-material properties of the Tecnis 1-peice designed to enhance stability are resistance to compression of the haptics in the capsular bag and an adherence between the optical surface and the capsular wall.

Analysing rotational stability

Fourteen sites were included in the trial that were based in the US and Canada and in total 174 eyes were implanted with the lens. Data in the trial was included for all toric first eyes from both study arms that had evaluable images between specified stability time points. This included 156 eyes, however, these did not necessarily have photographic data available for every follow up visit, which were set at 1 day, 1 week, 1, 3 and 6 months. "The FDA wanted to display stability over a 3 month interval so the initial 2 data points were 1 day to 3 months and 3 months to 6 months," said Dr Nixon.

The digital slit-lamp photographs were analysed by a validated custom and proprietary software that uses iris and/or scleral landmarks to align images from later time points to baseline. As a comparison, the team used the ANSI standard (Z80.30), which defines toric lens stability as >90% of lenses rotating ≤5° between visits that are 3 months apart.²

"When the study data was reviewed, the lens stability was so impressive that even the 1 day to 6 months exceeded the ANSI (Z80.30) guidelines for Toric IOLs," he added.