Eyeworld

49 EW FEATURE by Ellen Stodola EyeWorld Staff Writer Manual and auto Ks Dr. Garg said that manual and auto Ks can prove helpful in providing confirmation of other diagnostics. Dr. Hovanesian does not tend to use manual or auto Ks because he gets much more reliable results from the other machines. These only measure a couple of points on the cornea, he said. Meanwhile, topogra- phy is able to measure thousands of points, and the surgeon is getting a qualitative map. Surgically induced astigmatism (SIA) Calculating surgically induced astigmatism is important. "Surgical calculators rely on one's SIA when determining the final IOL orien- tation," Dr. Garg said. "If you are just estimating your SIA, this can introduce error." "It's essential to calculate the SIA because it's part of your equa- tion," Dr. Hovanesian said. There is a tool by Warren Hill, MD, that makes this calculation easy, where a surgeon can measure pre- and post- operative surgical astigmatism and determine what the SIA is. "For most people, if you want to guess, it's going to be about a half diopter of flattening wherever the clear corneal incision is," Dr. Hovanesian said. Manifest refractive error in toric IOL planning Manifest refractive error can help give physicians information about what the patient is used to. "This becomes important when considering toricity and the possi- bility of flipping the axis of astig- matism," Dr. Garg said. "Also, it is important to ensure that the ocular surface is without significant dry- ness/aberration prior to measuring for a toric IOL." Dr. Mah said that the surgical techniques associated with toric IOLs are the same as what surgeons are already used to. A lot of the equipment used for preoperative diagnostics are technologies that many already have in their practice. The thing that most people do is get optical biometry, he said, which can be done by using either an IOLMaster or LENSTAR. "It helps not only with sphere but also with cylinder because it does help with the keratometry and axis," he said. Dr. Mah will also get autorefrac- tion with keratometry value because there will be corneal cylinder or lenticular cylinder. What surgeons should operate on from a toric IOL standpoint is the corneal cylinder. Topography is essential in this process. "You want to make sure there's nothing else going on in the cornea so that it's not irregular astigmatism that you're trying to correct," Dr. Mah said. Driving toric IOL axis and power decisions There are a number of diagnostic tools available to measure IOL axis and to help make power decisions. Dr. Garg uses a number of these tools, including the IOLMaster, OPD III (Marco, Jacksonville, Fla.), and Pentacam (Oculus, Arlington, Wash.). "My IOLMaster determines spherical power and gives me one measurement of astigmatic axis," he said. Meanwhile, the OPD allows him to measure IOL power using Placido topography, as well as giving a wave- front measurement of the eye. "Lastly, my Pentacam allows me to measure both the anterior astigmatism as well as the posterior astigmatism—the true net corneal power," he said. Dr. Mah uses the axis from his topography readings and tends to take the power of keratometry from the optical biometry measurements. He also does a tomography to make sure that the patient is a LASIK or PRK candidate in case some en- hancement is needed. After taking care of the ocular surface and any other preoperative conditions, Dr. Hovanesian said that he primarily uses corneal topogra- phy and optical biometry, which can be accomplished with either the IOLMaster (Carl Zeiss Meditec, Jena, Germany) or LENSTAR (Haag-St- reit, Koniz, Switzerland). Manual keratometry can play a role, but it is less widely used because of other methods that are consistent and reliable. "The challenge comes when the results from the 2 instruments don't agree either at the axis or the magnitude of astigmatism," Dr. Hovanesian said. "I think you need to look at both measurements to have reproducible results." Physicians may want to deter- mine the axis based on topography, and primarily looking at the central 1–2 mm of the cornea will give you the best idea of the magnitude of astigmatism. The IOLMaster may underestimate the magnitude of astigmatism, he said. But he main- tained that it is important to look at both topography and the IOLMaster to be sure that your measurements make sense. Either topography or tomog- raphy may be necessary for success with toric IOLs. Dr. Garg said it is important to look for agreement between your various diagnostics. "The ocular surface is of utmost importance," he said. "It is very Surgeons discuss the preoperative diagnostics they use for toric IOL implantation T here are many things physi- cians can do to set them- selves and their patients up for success with toric IOLs. Preoperative diagnostics are a key factor, and there are a number of measurements and considerations for axis and power when implanting a toric lens. Sumit "Sam" Garg, MD, Gavin Herbert Eye Institute, Irvine, Calif.; John Hovanesian, MD, Harvard Eye Associates, Laguna Hills, Calif.; and Francis Mah, MD, Scripps Clinic, La Jolla, Calif., shared some of their pearls for preoperative management and what they think are the key factors for success. Preoperative diagnostics? Before taking measurements, it is important to address the ocular surface. "First, you need a healthy ocular surface that can yield reliable and repeatable measurements," Dr. Hovanesian said. In order to ensure that you have this, it is important to manage dry eye preoperatively, and it is also important to recognize other abnormalities, such as anterior basement membrane dystrophy, that could distort the surface and lead to irregular measurements, he said. June 2015 Toric IOLs Succeeding with toric IOLs AT A GLANCE • Surgeons should ensure that the patient's ocular surface is healthy prior to taking any measurements for toric IOLs. • The 3 companies with commercially available toric IOLs (Alcon, Abbott Medical Optics, and Bausch + Lomb) all have online toric IOL calculators. • A number of other toric IOL calculators are excellent resources. Barrett Toric Calculator Source: Graham Barrett, MD continued on page 50

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