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The Speed of Sound

Ultrasound for Retinal Detachment is about Ruling In, Not Ruling Out

Butts, Christine, MD

Emergency Medicine News: May 2019 - Volume 41 - Issue 5 - p 16
doi: 10.1097/01.EEM.0000558185.61617.88
The Speed of Sound

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Ocular ultrasound has always been one of my favorite applications for ultrasound at the bedside. We see tons of patients with visual changes, vision loss, and ocular trauma. Findings can be missed, even with a dilated eye exam under direct fundoscopy. I'll be the first to admit that I'm terrible with a fundoscope, which, to be honest, is the major reason I prefer ultrasound.

So I read with great interest the recent article, “Test Characteristics of Point-of-care Ultrasound for the Diagnosis of Retinal Detachment in the Emergency Department,” published in Academic Emergency Medicine. (2019;26[1]:16; http://bit.ly/2TEFutH.) The study authors compared point-of-care ocular ultrasound with the gold standard of a diagnosis provided by a retina specialist. A total of 115 patients with a complaint of floaters or flashes in one or both eyes were enrolled. Thirty EPs with varying degrees of experience participated, but they all underwent an hour-long training session and were expected to demonstrate adequate performance on one supervised practice scan. The sonographers were not blinded to the patient's history nor the suspected diagnosis.

Ultrasound had a sensitivity of only 75% in detecting retinal detachment, while specificity was 94%. (Acad Emerg Med. 2019;26[1]:16; http://bit.ly/2TEFutH.) Interestingly, the more scans an examiner performed, the higher the specificity but not the sensitivity. Examiners who enrolled one or two patients had a sensitivity of 80% and specificity of 71%, while those of examiners who enrolled three or more patients were 73% and 98%, respectively. Interestingly, two of the four false-negative studies actually had abnormalities but not retinal detachments. One demonstrated a posterior vitreous detachment and the other a retinal hemorrhage.

At first glance, these findings may make some think of ultrasound as less valuable in these patients, but I disagree. Ultrasound at the bedside should be about specificity, not sensitivity. It should be about ruling in, not ruling out. With utmost respect to our esteemed colleagues, we aren't radiologists. We have the benefit of knowing the patient presentation, history, and clinical exam.

Most of us have an idea of the diagnosis (or at least the top three) before we even touch a patient. In that respect, ultrasound is just another arm of the process. If a patient with uncontrolled diabetes and hypertension presents with a complaint of flashes in one eye, I'm thinking retinal detachment regardless of what I see on ultrasound. Ruling out a diagnosis should be based on our clinical judgment, not what an isolated ultrasound tells us. The late lawyer Johnnie Cochran famously said, “If it doesn't fit, you must acquit,” but I much less famously say, “If your ultrasound doesn't fit, don't quit.”

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Dr. Buttsis the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans. Follow her on Twitter @EMNSpeedofSound, and read her past columns athttp://bit.ly/EMN-SpeedofSound.

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