Each year, strokes afflict about 600,000 Americans-killing almost 160,000 and disabling many others. Most occur without warning. Magnetic resonance imaging and arteriograms can detect conditions that presage stroke but are expensive, time consuming and sometimes painful. A new sensor that sits on the eyelid may provide a cheap, noninvasive method of screening for brain aneurysms (bulges in blood vessels that can burst, depriving the brain of blood) and for blockages that can limit blood to the brain.

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