Improved Stability in Toric IOLs

Surgeons have two methods for correcting pre-existing corneal astigmatism during cataract surgery: We can perform arcuate incisions (typically limbal relaxing incisions or some modification of LRIs) or we can implant a toric IOL.

In the UK, there are numerous toric IOLs available to us from Acri.Tec, Alcon, Abbott Medical Optics (AMO), Oculentis and Rayner; some are also available in a toric multifocal platform. My personal threshold for implanting a toric lens over LRIs is fairly high, at about 2.0 D of astigmatism, as I have confidence in my corneal astigmatic surgery. It is slightly lower for implanting a toric multifocal lens, however, at about 1.5 D.

From among the many options, one should look for toric IOLs that offer good optical performance, excellent visual quality, with good alignment and excellent rotational stability. Ease of use for the surgeon is also a factor.

Toric iol outcomes

We recently took part in a multi-centre study to evaluate visual acuity and patient satisfaction following implantation of one of the newer toric lenses, the Tecnis Toric (AMO), an open-loop hydrophobic acrylic IOL (Figure 1). The lens was implanted in 65 eyes with >0.75D of preoperative astigmatism, all undergoing routine cataract surgery. Postoperative assessments were performed four to eight weeks after surgery.

The mean cylinder was reduced from -1.96 ± 1.04 D pre-op to -0.66 ± 0.53 D post-op. Best-corrected visual acuity went from a mean of 20/40 pre-op to 20/25 post- op. Mean postoperative uncorrected visual acuity was 20/30. Perhaps most importantly, we have seen very high rates of overall patient satisfaction (Figure 2), with hardly any photic phenomena.

The length of this lens (13mm) provides good contact between the capsular bag and IOL during the early postoperative period. This, in turn, means there is increased friction to help keep the lens stable. Acrylic lenses have also been reported as being rotationally more stable than silicone; C-loop lens designs do have the potential to rotate clockwise under capsular compression, but I think rotation here is minimal, as evidenced by the patient satisfaction and visual acuity.

Pearls for success

In my experience, achieving excellent visual outcomes with a toric lens is dependent on two things: Precise axis placement initially, followed by rotational stability postoperatively.

For precise placement, we are limited by the inherent errors in corneal power measurements and reference marker placement. For example, the width of the corneal mark can easily introduce 5° of error. Keep in mind that for every 10° the lens is off-axis, there is a 33 per cent loss of efficacy.

My preference is to obtain corneal topography on all patients and rely on this, more than the biometry, for the magnitude and axis of astigmatism. I am convinced surgeons have to be obsessive about ensuring correct lens alignment with the visual axis. Once aligned, watch out for sudden decompressions of the globe that may cause the lens to rotate.