EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/227001
February 2014 December 2013 What's ahead in2011 EW FEATURE 39 Posterior corneal astigmatism's role increasingly recognized by Erin L. Boyle EyeWorld Senior Staff Writer AT A GLANCE • New ways of measuring posterior corneal astigmatism have demonstrated its role in residual astigmatism after toric IOL implantation. • Future innovations could allow true measurement of corneal refracting power. • Patients who have with-the-rule astigmatism are often overcorrected, while patients who have against-the-rule astigmatism are often undercorrected when posterior corneal astigmatism is not accounted for, an expert said. ments," said Dilraj S. Grewal, MD, and Surendra Basti, MD, Department of Ophthalmology, Northwestern University Feinberg School of Medicine, Chicago. They conducted a study examining the relationship between the anterior and posterior corneal astigmatism in a cohort of normal eyes with >3 diopters of astigmatism (28 patients) and ectatic eyes (22 pa- tients). In the study, they found a greater contribution of the posterior surface to the total corneal astigmatism in normal corneas (31±8.5%) when compared to keratoconic eyes continued on page 40 Measurement of posterior corneal astigmatism is important in achieving the best toric IOL results, experts say W hen a toric lens has been implanted but results are not visually optimal—or expected —posterior corneal astigmatism might play a role in that discrepancy, experts say. "I think many cataract surgeons who have used toric lenses can remember cases where they were scratching their heads postoperatively," said D. Rex Hamilton, MD, director, UCLA Laser Refractive Center, and associate clinical professor of ophthalmology, Jules Stein Eye Institute, Geffen School of Medicine at UCLA, Los Angeles. "You look in the eye with dilation, you can see the orientation of the lens, it's exactly where you wanted to put it, and yet the patient ends up with residual astigmatism." Posterior corneal astigmatism can explain that issue, he said. New findings and ways of measuring the back of the eye have discovered that the posterior corneal surface contributes to the total corneal astigmatism. "The effect of the posterior corneal astigmatism, whose meridian may be different from the axis of the anterior corneal surface meridian, explains why in some eyes the results with toric IOLs are less than ideal despite seemingly appropriate IOL selection and placement based on good anterior corneal measure- Only One System Delivers the Shield of PROTECTION. DuoVisc® Viscoelastic System offers both the endothelial protection of chondroitin sulfate in VISCOAT® OVD with the proven mechanical protection and space maintenance found in PROVISC® OVD.1 1. DuoVisc® OVD Product Insert. © 2013 Novartis 1/13 VIS13003JAD One System. No Compromises.