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The Speed of Sound

The Speed of Sound

Forget Fundoscopy; Ultrasound Can Diagnose Eye Complaints

Butts, Christine MD

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doi: 10.1097/01.EEM.0000462403.64295.97
    Figure. I
    Figure. I:
    mage 1. Normal-appearing eye. The retina appears as a hypoechoic (gray) lining that is flat and contiguous with the globe. Locating the optic nerve sheath (star) at the back of the eye will guide the EP to the expected location of the optic disc (arrow).
    Figure
    Figure

    Many EPs struggle with fundoscopy and dread complaints that require this exam. It can be difficult to get a clear image of the retina and to localize the optic disc and vessels even in the most cooperative patients. Dilating the pupil can make this evaluation more straightforward, but many EPs may not feel confident in making a diagnosis even with a good view of the optic disc. (Image 1.)

    Consider this 35-year-old woman who presented to the ED with a complaint of recurrent headaches and intermittent blurred vision. The physical exam is mostly unremarkable, although attempts at direct visualization of the optic disc by fundoscopy are unsuccessful. The remainder of the neurologic exam is normal, and a CT scan of the head is without focal findings. An ultrasound is performed. (Image 2.)

    The patient presented with signs and symptoms concerning for elevated intracranial pressure, specifically idiopathic intracranial hypertension (IIH). IIH can be diagnosed in a number of ways, however. Typically, the diagnosis is initially suspected by a finding of elevated opening pressure on lumbar puncture in the absence of other causes (mass, etc.). EPs commonly make this diagnosis, usually by identifying key features of the patient history (headache, visual disturbance, etc.) coupled with lumbar puncture and imaging. Identifying the signs of elevated intracranial pressure, mainly papilledema, is key to pursuing further testing in these patients.

    Ultrasound can be used at the bedside to assess for papilledema and other signs of elevated intracranial pressure. A high-frequency transducer should be used to obtain sufficient resolution. The transducer should be placed lightly on the closed eyelid to minimize pressure on the globe. Ultrasound gel can be placed directly on the transducer or the eyelid. The globe is easy to identify, and the posterior retina should be sought to identify the location of the optic disc. Typically, the optic disc is flat, and is not typically discernible from the remainder of the retina.

    Figure. I
    Figure. I:
    mage 2. Papilledema as seen on ultrasound. The optic disc is seen to be “heaped” or “bubbled” up at the posterior aspect of the retina, consistent with papilledema.

    When papilledema is present, the optic disc will appear elevated or “heaped up.” Some describe its appearance as a bubble. Identifying this finding bilaterally is consistent with diffusely elevated intracranial pressure, and may lead the EP to consider more advanced testing such as lumbar puncture or MRI.

    Next month, I will evaluate ultrasound of the optic nerve sheath itself as another measurement of elevated intracranial pressure.

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