Eyeworld Daily News

EW SHOW DAILY 26 ASCRS Symposia Tuesday, May 10, 2016 34.61 mm, a ACD of 4.03 mm, mean K of 43.64 D, WTW of 11.9 mm, and lens thickness of 4.76 mm. What formula do you choose? After some discussion among the panel—including Dr. Kohnen saying he would use the Haigis formula and Dr. Slade comment- ing that he would like to know if this was the patient's dominant or non-dominant eye—Dr. Donnenfeld weighed in and said his first prefer- ence would be to use intraoperative aberrometry. Dr. Donnenfeld also said he is "very comfortable" leaving the patient aphakic for a couple of days and putting an IOL in later based on their postop refraction. "I almost always end up making the patients hyperopic when I go with these formulas," Dr. Donnen- feld said, expressing an issue many others on the panel said they have as well. Dr. Barrett said he would use his own formula (the Barrett Universal II) in this case, but he added "you have to use an adjustment to get a result with a high myope. … You cannot use your standard constants and expect a good result." When asked at what axial length do you need to consider these adjustments, Dr. Barrett said axial length is not the only factor. "Even more important, is when you get to a negative lens, that's when my theory is that the math has to be different; that's when you run into real problems unless you do something special," he said. "So it's not just the axial length. When the lens is above 5 or 6 D, even without adjustment before, you do pretty well. When you compare formula in +6, +7, +8 D—it is a matter of K and axial length that gives you that lens—there may be some small differences in the formula that don't matter. It's when they become meniscus and particularly when they become negative; so it's not just the axial length, it's a combina- tion of axial length and K. You can tell usually by where the lens is. So anything less than 6 D or so, you've got to be thinking about this trans- formation." Dr. Barrett presented several more cases, including what formula to use in a LASIK patient, a previous RK patient, a patient with hypero- pia, and more. When it came to the LASIK patient, Dr. Barrett said that for- mulas such as the Barrett True K, Haigis, and the ASCRS calculator, for example, resulted in pretty good prediction errors. "The message I want to leave you with here is that the formulas that have done well are the ones where the refractive history is known. It's so easy to see a patient and ask what their refractive history was before LASIK," Dr. Barrett said, adding that if they don't know, it's worth having them try to find out. "If you have the refractive history, you will do better." Dr. Koch said clinicians have to be particularly careful with expec- tations when it comes to LASIK patients. "I think a healthy skepticism and a preop skepticism shared with your patient is mandatory despite the vast improvements we've seen. I think we're doing so much better, but I would much rather nail it and have them be ecstatic than be off by a diopter and not have them feel that we met what we promised," he said. RK example is another example, Dr. Barrett said, where having a prior refractive history can be helpful in IOL calculations. Dr. Zaldivar said cataract surgery in RK patients is the 1 time he will make the incision between the limbus and the sclera, not the cornea, in order to preserve the structure. Dr. Donnenfeld called previous-RK cataract patients the "most difficult cases I manage" due to irregularity of the cornea and potential for vision fluctuation throughout the day. He added that he's been happy with results in these patients when he has performed crosslinking first. For the patient needing a toric IOL, the panelists brought up the issue of posterior astigmatism. They discussed how no device is quite there yet when it comes to offering accurate posterior corneal astigma- tism measurements, leading many of them to use the Barrett toric calculator or Baylor nomogram to compensate for the posterior corneal astigmatism. EW continued from page 24

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