Eyeworld

66 | EYEWORLD | SPRING 2026 R EFRACTIVE by Liz Hillman Editorial Co-Director About the physicians Nicole Fram, MD Advanced Vision Care Los Angeles, California Douglas Koch, MD Department of Ophthalmology Cullen Eye Institute Baylor College of Medicine Houston, Texas A ttend a session on cataract sur- gery and astigmatic correction at a medical conference and you'll hear about the importance of K alignment ad nauseam, but Nicole Fram, MD, said it continues to be a relevant and important point to emphasize. "1) When K values don't align, ocular sur- face disease is a very common cause. 2) I think astigmatic correction is critical to the success of refractive cataract surgery. We're seeing reimbursements going down, and we're seeing expectations from patients going up. The first step to getting comfortable with presbyopia-cor- recting lenses, in my opinion, is knowing how to reliably correct astigmatism. … If you don't feel comfortable treating astigmatism or knowing when to treat astigmatism, you can never ele- vate your practice into the presbyopia-correcting world, which is not only what patients want but it's also what doctors are going to need to survive [financially]," Dr. Fram said. Dr. Fram and Douglas Koch, MD, discussed the topic of when the Ks don't align—when mis- alignment is clinically significant, what can be done about it, and how it impacts lens choices. K discrepancies Dr. Koch said everyone has their own threshold for K measurements that don't align, meriting remeasurement and potentially further action. "For me, it would be any difference in astig- matism magnitude that's greater than a half or certainly greater than 0.75 D. For astigmatism meridian, in general I would like measurement variations in the steep meridian of no more than 10 degrees," he said. He provided the accuracy of meridional alignment as a function of the astigmatism magnitude needed to leave the patient with <0.5 D of refractive astigmatism: • 1 D: ≤14° • 2 D: ≤7° • 3 D: ≤4° • 4 D: ≤3° For eyes with low amounts of astigmatism, there is some flexibility, but accuracy within even 15 degrees can be a big ask if the magni- tude of astigmatism is small, i.e., less than a half diopter. "You might ask why consider correcting 0.5 D? For the patient with against-the-rule astigmatism, not treating 0.5 D on the cornea will lead to up to 1.0 D in refractive astigma- tism, and this will increase over time," Dr. Koch said. "Fortunately, it's easier to get agreement on the steep meridian when the astigmatism magnitude is greater because it's a more defined point with increasing magnitudes." Dr. Koch mentioned a study that compared the steep meridian difference between two devices—the IOLMaster (Zeiss) and the Lenstar (Haag-Streit)—in the same visit for 129 right eyes. The devices agreed on the location of the steep meridian within 5 degrees 60.5% of the time and within 10 degrees 82.9% of the time. This highlights the importance of taking multi- ple measurements, he said. If you only have one device for K measure- ments, Dr. Koch said you need to think about how to verify the information that device is giving you. "Everyone uses a biometer with LEDs to measure the K readings, and everyone should have a topographer, preferably one with Placido rings because of the detail it gives about the ocular surface," Dr. Koch said. "Ideally [you should also have] a device that gives you When the Ks don't align continued on page 68 Corneal imaging of an eye with poor vision following implantation of a trifocal lens. Placido mires show subtle distortion just below midline, and irregular astigmatism is evident, particularly in the instantaneous radius of curvature map. A subtle corneal subepithelial scar was evident on slit lamp examination. Source: Li Wang, MD, PhD

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