The ability to safely and predictably correct astigmatism at the time of cataract surgery has been a boon to refractive cataract practices — and to our astigmatic patients. Below are six pearls for successful toric IOL outcomes.
1. Accuracy of the axis and
magnitude of astigmatism. In my experience, mistakes in measurement are the most likely source of errors with toric IOLs. I recommend using multiple devices to identify the axis and magnitude of astigmatism and make sure they are in rough agreement. The smaller the amount of astigmatism, the harder this can be. Posterior corneal astigmatism should be factored in to the calculations. Irregular astigmatism, often due to epithelial basement membrane disease or dry eye, should be addressed prior to IOL power and axis determinations.
2. Targeting the astigmatic correction. Adopting a treatment strategy aiming for plano results means accounting for posterior corneal astigmatism. As such, we approach with-the-rule (WTR), against-the-rule (ATR) and oblique astigmatism differently. In general, we aim to overtreat ATR, undertreat WTR and fully account for oblique astigmatism. Typically, I aim for 0.25 D to 0.30 D of residual WTR astigmatism. It is perfectly acceptable to flip the axis from ATR to WTR.
3. Optical quality. Whenever there is the potential for visual degradation due to other factors — ocular surface disease, residual refractive error or even IOL rotation — the optical quality of the IOL should be a major consideration. The Johnson & Johnson Vision Tecnis platform, with its advanced aspheric and chromatic aberration control, helps surgeons start out with the highest quality optics to minimize the impact of other issues.
4. Intraoperative alignment. The cornea should be marked at 3 and 9 o’clock preoperatively with the patient sitting upright. I program 10° intrastromal arcs at the intended axis of astigmatism correction into my femtosecond laser to provide an additional intraoperative and archival landmark to check the position of the toric lens. There are a number of new intraoperative technologies that can also facilitate toric IOL registration and alignment, such as TrueVision (TrueVision Systems), Callisto (Zeiss) and others.
5. Stability of the IOL. David Chang, MD, and colleagues have shown that all toric lenses have the potential to rotate, but that the vast majority rotate 5° or less. While the Tecnis toric IOLs in the study were more prone to rotation than the Acrysof toric IOLs (Alcon), refractive outcomes were the same in both groups. I believe this is due to the outstanding optical quality of the Tecnis toric IOL platform, which has been shown to retain excellent outcomes even when rotation and refractive error are deliberately induced in laboratory testing.
6. Surgical technique to prevent misalignment. A perfectly round and sized capsulotomy centered on the capsular bag should increase the chance of sufficient and uniform capsule overlap of the optic, thereby reducing the chance of lens tilt and associated aberrations. Once the IOL is placed, be sure to completely remove OVD from behind the IOL and seat the lens into the posterior portion of the capsule by gently applying posterior pressure on the central optic at the end of the case. Leave the eye at normal tension with good wound closure and remind patients that the eye is a “no fly zone” for the first day postop (i.e., no eye rubbing or even wiping drops away).
Disclosure: Waring reports he is a consultant for Johnson & Johnson Vision.