Eyeworld

EW GLAUCOMA 74 February 2016 retinal thinning on serial imaging, Dr. Liu said. Anatomic variation in the dis- tribution of the RNFL can also lead to artifacts. The RNFL is typically thickest superiorly and inferiorly. In some patients, the superior or inferior peaks can be shifted circumferentially. In these individu- als, the OCT software may report su- perior thinning if the superior peak motion, and scan centration issues can all result in scan artifacts, Dr. Liu said. These can often be minimized with careful training of operators. Other sources of artifacts can be patient-specific. A common source of OCT artifacts is myopia, Dr. Budenz said. "Up to 50% of moder- ate to high myopes will have repeat- edly abnormal OCT scans," he said. Vitreomacular traction can also affect scan integrity in several ways. Traction on the retina can increase retinal thickness, making the RNFL look thicker than it is. Also, the distortion of retinal architecture can cause segmentation errors, resulting in variable OCT artifacts. Over time, if vitreomacular traction releases, the retinal architecture can be restored, which can look like progressive is not in the superior sector of the scan. These issues can often be easily identified by looking at the RNFL thickness maps on the scan outputs, according to Jullia Rosdahl, MD, PhD, Durham, N.C. RNFL thickness values Once a scan is deemed of acceptable technical quality and free of arti- facts, the RNFL data can be evaluat- ed. The values are typically reported both globally and by circumferential sectors and represent average RNFL thickness in microns in each sector. To aid in the interpretation of these values, each approved device has a reference database of RNFL values obtained from variable num- bers of healthy subjects. Individual patient values are compared to these normal values to determine if the patient's RNFL is statistically likely to be similar to or different from the mean values seen in the normal population sampled in the reference database. A lower than expected RNFL value will typically be reported in yellow or red ink if the value is con- sidered to be borderline or abnormal compared to the reference database. RNFL value may represent RNFL loss associated with glaucoma or other ocular conditions, but may also arise due to artifacts or outlying but normal RNFL values. Another key pearl: Statistically different from the normal mean does not mean abnormal. Some nor- mal people—such as very tall people or those with longer axial lengths— have outlying biometric parameters that are statistically abnormal but clinically entirely normal. Systematic approach A systematic approach to OCT inter- pretation should include assessment of scan signal strength, accuracy of segmentation, the presence of artifacts, and assessment of RNFL thickness, Dr. Budenz said. This approach can reduce the rate of so-called "red disease," which occurs when healthy subjects have abnormal test results (printed in red ink on the test output). EW Editors' note: The physicians have no financial interests related to this article. Contact information Liu: yaoliumd@gmail.com Rosdahl: jullia.rosdahl@duke.edu (800) 367-8327 DuPont, WA 98327 info@lacrimedics.com • www.lacrimedics.com ©2016 Lacrimedics, Inc. 1 ASCRS Clinical Survey 2015. Global Trends in Ophthalmology and the American Society of Cataract and Refractive Surgery. 2 Offer valid through April 30, 2016. Don't let 41% of your patients with OSD go untreated, especially when they need something more than artifi cial tears. Lacrimedics' VisiPlug® is FDA approved for the treatment of the Dry Eye components of varying Ocular Surface Diseases (OSD) and after surgery to prevent complications due to Dry Eye Disease. VisiPlug® - Provides approximately 180 days of occlusion. Call 1-800-367-8327 and receive 15% OFF 2 your order! (Mention promo code OSD0416.) Don't let 41% of your patients 41% of refractive or cataract surgery patients have ocular surface dysfunction levels requiring some treatment beyond artifi cial tears! 1 0.4mm 0.5mm Pearls and pitfalls continued from page 72

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