EyeWorld India March 2013 Issue

March 2013 13 EWAP FEATURE When performing LRIs, the main points are careful positioning, careful measure- ments, and careful placement Source: Louis D. Nichamin, MD and stability,” he said. “If you have access to a femtosecond laser for cataract surgery, there’s no question that the incisions are more accurate and more pristine than a blade-created incision,” he said. Dr. Tipperman also described Richard Mackool, MD’s penetrating LRI nomogram, “where surgeons take their keratome of choice (2.2- 2.5) and make one or two phaco incisions directly on axis to reduce the corneal astigmatism.” These PLRIs are used just before the viscoelastic is removed at the end of the case, he said. The nomogram shows that for 1.5 D of against-the- rule (ATR) astigmatism, surgeons should make two 3.2-mm incisions 180 degrees apart. “If you average 100 patients, you’ll have the 1.5 D of correction. But some will have zero effect and others will have a 2.5-D effect,” Dr. Tipperman said. “And that’s the issue with incisional keratotomy—you may on average get your desired effect, but there’s going to be variability that’s hard to control.” Dr. Donnenfeld uses every technique available but finds he uses diamond knives “more at the slit lamp to adjust the results in patients who have surprises postoperatively.” Dr. Tipperman recommends surgeons keep the blades perpendicular to the limbus and “go slow.” Study the patient’s topography “and make sure it’s symmetric and looks good before treating,” he said. “It’s amazing the number of people who want to treat based on keratometry readings alone.” LRIs Last year’s ASCRS Innovator’s Lecture clarified what “posterior corneal astigmatism” is (courtesy of Douglas Koch, MD). Dr. Nichamin said “one of the ramifications of [this work] is that we now have further evidence that with-the-rule (WTR) astigmatism behaves differently than ATR, and that’s due in part to the posterior corneal contributions.” Dr. Nichamin’s LRI nomograms have “for many years” been divided into two separate tables—one for WTR and the other for ATR. “I’m probably a bit of an anomaly because I separate them— it’s not significantly different, and almost in the same ratio as what [Dr. Koch] has pointed out in terms of quantified differences that occur in the posterior corneal measurements in the setting of toric IOL use,” Dr. Nichamin said. As such, Dr. Koch’s recent findings with regard to ATR versus WTR astigmatism and its varying response to correction through the use of toric implants parallels what he has experienced when utilizing LRIs. “There’s still much that we don’t understand and until recently, did not measure very well either.” For instance, the limbus is a little closer to the visual axis at 6 and 12 o’clock as compared to 9 and 3 o’clock, and “inter-” as well as “intra”- corneal meridional differences can complicate calculations; traditional measurements tend to occur only at two points in each meridian, which may not be sufficient. Surgeons have also seen meridional differences between Occidental and Asian eyes. “I’ve been a big proponent of LRIs for a long time, but one of the concerns with these incisions is that every patient responds differently based on multiple parameters,” Dr. Donnenfeld said, adding Dr. Koch’s work has helped to clarify some of those discrepancies. “It’s more of an art form than science, and LRI results can be variable even in the hands of the best surgeons because of the patient variability.” LRIs remain a reasonable option for anything under 1.0 D or 1.5 D, Dr. Tipperman said, but “based on Dr. Koch’s work, maybe we should limit that to 0.75 D or 1.25 D if they’re WTR.” Dr. Nichamin suggested that all surgeons continually adjust and refine their nomograms and start thinking of them as fluid measurements rather than static ones. Femtosecond laser Dr. Donnenfeld has begun performing arcuate incisions with a femtosecond laser “because the accuracy is uncanny,” he said. “The incisions are perfectly symmetric so there is less irregular astigmatism and none of the surgeon variability that can be present with manual LRIs.” With the LenSx (Alcon), he uses a 9 mm optical zone, and an 8 mm optical zone with the IntraLase (AMO). By titrating the incisions, “we’re achieving superior outcomes. Before the femtosecond laser, any incision we made was permanent,” he said. The femtosecond laser continued on page 14