Eyeworld Supplements

W ith about 65% of older patients present- ing with corneal astigmatism between 0.25 D and 1.25 D, the need to offer a solution to these patients will continue to grow. In my patient population, 35% of patients have astigmatism of 0.75 D and above, and I implant an AcrySof IQ Toric IOL (Alcon, Fort Worth, Texas) in a significant number of these patients. Most ophthalmolo- gists agree that 0.5 D of astigmatism translates to about 0.25 D of spheri- cal error and can negatively impact high contrast visual acuity. With that in mind, any reduction in post-op astigmatism of more than 0.5 D will impact visual acuity. The AcrySof Toric IOLs have been on the U.S. market since 2005, with the lowest IOL cylinder power of 1.50 D, and I think these lenses should be the primary treatment consideration for patients with pre-existing corneal astigmatism and corneal cylinder as low as 0.75 D. I think it's equally crucial that we know what degree of surgically induced astigmatism (SIA) we're introducing during the procedure. A personal interest of mine has always been methods to reduce SIA. Wound geometry and location certainly play a role—surgeons will have lower SIA levels if the wound geometry is square and placed at the posterior limbus. My SIA for a square wound originating at the posterior limbus is 0.25 D with a standard deviation (SD) of 0.14 D. Clear corneal incisions have a higher SIA and wider SDs. We have recently shown that 2.2 mm square posterior limbal incisions induced significantly less SIA relative to similar-sized clear corneal incisions. 1 More importantly, that same study showed the SIA was significantly less variable as well. Furthermore, for patients with lower levels of astigmatism (i.e., 0.75 D), the wound architecture and location play the most significant role. It is my opinion that it is difficult to treat 0.75 D if you fall into the category of having an SIA of 0.6 D with an SD of 0.4 D. For a high level of astigmatism —3.5 D or 4.0 D—SIA is not a relevant factor. I think there's a tendency for surgeons who use clear corneal incisions to avoid using the AcrySof T3 Toric lens because their outcomes are less predictable. They may be unaware that it could be the incision that's causing the inconsistent outcomes and not the lens itself. I was involved in a study evaluating the refractive results of the AcrySof T3 Toric and AcrySof IQ EW Chicago 2012 5 What impact does SIA have on treating pre- existing corneal astigmatism with a toric lens? Figure 1. Distribution of post-op refractive astigmatism by IOL type by Paul Ernest, M.D. What role does advanced technology play in your practice? " These lenses should be the primary treatment consideration for patients with pre-existing corneal astigmatism and corneal cylinder as low as 0.75 D " Paul Ernest, M.D. continued on page 6 Alcon Sunday supplement_Chicago2012-12pages_Layout 1 4/20/12 4:50 PM Page 5

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