Eyeworld

EW REFRACTIVE 80 March 2019 Refractive editor's corner of the world by Michelle Stephenson EyeWorld Contributing Writer Technologies, formulas surgeons are using to calculate IOL power A ccording to John Ber- dahl, MD, Sioux Falls, South Dakota, now that immersion A-scans are providing consistent axial lengths and biometry has transi- tioned to providing more accurate Ks and measuring anterior chamber depth or lens thickness, surgeons are including topography and retinal thickness when evaluating poten- tial lenses. "We get our K values from the biometer, but we also get a topography to make sure that is reg- ular because our biometry does not give us topography. This is helping people get the right lens in the eye," Dr. Berdahl said. Dr. Berdahl uses the LENSTAR biometer (Haag-Streit, Koniz, Switzerland), but said that the IOLMaster 700 (Carl Zeiss Med- itec, Jena, Germany) does a great job, too. "Additionally, new swept source OCTs that are coming out to do optical biometry will be great as well," he said. Douglas Koch, MD, Houston, agreed. "I use both the IOLMaster 700 and LENSTAR. I prefer using two because I sometimes find disparities in the two measurements, and those can give me a clue to go back and re- evaluate the ocular surface or remea- sure. In terms of in-the-clinic use, our team prefers the IOLMaster 700 because it's easy and fast to use, and it's robust about getting good axial length measurements through dense cataracts. I also like the fact that it has what's called telecentric keratom- etry, which means that it measures corneal curvature relatively indepen- dent of the distance from the device to the cornea. That seems to give a bit of a boost to the accuracy. A nice advantage of the LENSTAR is that is has the Hill-RBF formula, which is one of our favorites," he said. Formulas Dr. Berdahl's go-to formula is the Hill-RBF. "I use that in every situa- tion that is within bounds. If it's out of bounds, I use the Barrett Univer- sal formula. Those two formulas usu- ally line up well. In extreme cases, I'll use aberrometry as well, and in post-refractive situations, I use the ASCRS Post-Refractive Calculator," he said. Dr. Koch uses the Barrett, the Hill-RBF, and the Holladay 1 for all cases. In long eyes, he uses the Holladay 1 with a Wang-Koch axial length modification. "I still find this to be my most accurate way to calculate IOL power in axial myopes over 26 mm. In short eyes, I add the Holladay 2, which I think is helpful. Although in short eyes, we have found that none of the formulas are as accurate as we'd hoped, so I some- times will try to do an average of them in order to get the best result," he said. Bryan Lee, MD, JD, Altos Eye Physicians, Los Altos, California, is using Hoffer Q, SRK/T, Holladay 1, Barrett, and Haigis for every patient. He often uses Holladay 2 as well. Making adjustments Although surgeons are still analyz- ing their outcomes data and making adjustments based on outcomes, they make fewer adjustments than they have in the past. "This is be- cause we've made them along the way," Dr. Berdahl said. "We don't make adjustments to our A-con- stants frequently because we've done all of that work along the way. IOL power choice in advanced cataract surgery T hanks to the implant, cataract surgery is the most powerful form of refractive surgery. Whether a patient is comfortable wearing glasses after cataract surgery or desires spectacle independence, modern day implant power formulas have made cataract surgeons more accurate. There are variables, though, that despite our best efforts, limit our refractive accuracy. Advanced formulas have helped tremendously. Understanding how these newer formulas calculate lens power can help cataract surgeons increase accuracy significantly. Knowing how a cataract surgeon can take advantage of a formula for a particular situation can help our accuracy even more. In this column, my partner John Berdahl, MD, and colleagues Douglas Koch, MD, and Bryan Lee, MD, share their wisdom on how to achieve a fundamental goal of cataract surgery: optimization of the refrac- tive outcome to achieve a patient's visual hopes and expectations. Thank you to Drs. Berdahl, Koch, and Lee for expanding our knowledge in the advancing field of intraoc- ular lens implant calculation formulas. Vance Thompson, MD, Refractive editor Intraoperative aberrometry used to refine the IOL power Source: John Berdahl, MD

• Blank Page
• Blank Page (1)