Eyeworld

EW CATARACT 24 August 2018 by Liz Hillman EyeWorld Senior Staff Writer YES connect way you get more detail, but you can also get more noise. We look at both maps, since they each can provide useful information. I like to use axial maps to assess astigmatism, but I think instantaneous maps will often give you the cornea's true shape and highlight irregularities and subtle sources of vision loss. Attendee: With the Pentacam (Oculus, Wetzlar, Germany), which Ks are used for astigmatism man- agement in cataract surgery (toric or LRI)? Dr. Miller: I have a Galilei G6 (Ziemer, Port, Switzerland) and a Pentacam HR, but I tend to use the Pentacam more. The Pentacam produces simulated keratometry values, so it will give you the Sim Ks of the anterior cornea that a corneal topographer would produce. But the Pentacam also measures the posteri- or surface, calculating total corneal power and total corneal astigma- tism. So that's what I use now; I use the total corneal astigmatism and put those Sim Ks into the appropri- ate formulas. Dr. Weikert: I use the Galilei, which combines Placido and Scheimpflug imaging, and I don't have access to a Pentacam. Since the Galilei is a tomographer, it can also provide the total corneal power by ray tracing light through the anterior and posterior corneal surfaces. When we maps, the software assumes that light rays, as they travel through the cornea and entrance pupil, all intersect somewhere along the op- tical axis of the eye. Instantaneous maps don't make that assumption; they allow rays to intersect wherever they actually do, and often times that's off the optical axis. What does that mean when you display those maps? You get a greater smooth- ing function with axial maps. The cornea will look smoother than perhaps it actually is. If you want to see the hills and valleys, the little bumps, the little dry spots, then you look at the instantaneous or tangential map. For astigmatism planning, I use axial maps, and if I'm trying to trouble shoot an eye that's not seeing all that well and doesn't refract very well, I will often use a tangential map to highlight subtle pathology. Dr. Weikert: It's the same data, just analyzed two different ways. Axial curvature looks at a point on the corneal surface and references the radius of curvature at that point to the visual axis. By tying the surface curvature at every point to the visu- al axis, the devices end up averaging the curvature. You may lose a little detail, especially in the peripheral cornea, but this method can reduce a lot of noise. Instantaneous maps determine curvature by looking at small areas adjacent to the point of interest and don't tie their analysis to the visual axis. By doing it this An ASCRS Young Eye Surgeons (YES) Clinical Committee-sponsored webinar featured an in- depth discussion about preoperative diagnostics for cataract surgery M itchell Weikert, MD, associate professor and residency pro- gram director, Cullen Eye Institute, Baylor College of Medicine, Houston, and Preoperative diagnostics for cataract surgery T he stakes are higher than ever to achieve an optimal refractive result after cataract surgery. It is imperative that we know what preoperative tools we have and how to interpret them to come up with an optimal plan for our patients. In this month's "YES connect" column, we highlight some important questions that came up during the recent ASCRS webinar "Know Your Tools/Toy Box: Preoperative Diagnostics." Although you may have different tools available in your office than the ones reviewed in the webinar, there is a common theme that can be applied to your individual practice. Understanding the ins and outs of your topographers and biometers can give you confidence that your lens selection and surgical plan are providing you every advan- tage possible for an optimal outcome. For those of you in training, I recom- mend that you expose yourself to and fa- miliarize yourself with all the different tools you have access to now in your program, as there is a good chance that you will have a similar device in your practice after training. Alternatively, if you are already in practice, perhaps at some point you may want to pur- chase a new topographer or biometer, and this webinar may help guide your decision on what device to purchase. This column launches a new pair of "YES connect" co-editors, and David Crandall, MD, and I are excited to be involved. Samuel Lee, MD, YES connect co-editor continued on page 26 Notice the irregularity in the patient's mires in the left image compared to the right image after a phototherapeutic keratectomy Source: ASCRS Kevin M. Miller, MD, Kolokotrones Chair in Ophthalmology, chief of cataract and refractive surgery, Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, provided expert insights for "Know Your Tools/Toy Box: Preoperative Di- agnostics." The webinar was hosted by YES Clinical Committee members Zaina Al-Mohtaseb, MD, Houston, and Samuel Lee, MD, Sacramento, California. It included specific case examples in which Dr. Weikert and Dr. Miller shared their thoughts on topography, tomography, biometry and specific differences among pre- operative diagnostic devices; their experience with different calculators and formulas; and their perspective on handling special circumstances like how long to wait before taking measurements after a patient stops rigid gas permeable lens use or has a Salzmann's nodule removed to ensure reliability. EyeWorld caught up with Dr. Weikert and Dr. Miller after the webinar so they could answer a few questions from attendees of the we- binar, as well as follow-up questions that expound upon the topics that were discussed during the hour-long educational event. Attendee: What is the difference between axial curvature and instan- taneous curvature? Dr. Miller: On some machines, axial is called sagittal and instantaneous is called tangential. With axial

• Cover