Chloe started everyday the same way: waking up with a heavy, throbbing pressure right behind her eyes, as if her head had spent the night in a vice. After an hour upright and a large mug of black coffee, the pressure would dull to a manageable ache. "Dehydration and clenching your jaw in your sleep," her friends told her. She bought a mouthguard and an orthopedic pillow. Then the weird symptoms started. Whenever she bent down to tie her sneakers or stood up quickly from her desk, her vision completely blacked out for three to five seconds, like a TV losing signal, before flickering back to normal. At night, lying in the dark, she began hearing a rhythmic, whooshing sound in her left ear, perfectly synced to the beat of her pulse. Whoosh. Whoosh. Whoosh. She assumed it was low-grade tinnitus from wearing earbuds all day. She booked an eye exam only because the brief blackouts were starting to freak her out when she exercised. She wanted to make sure she didn't need stronger glasses. Chart test: crisp 20/20 in both eyes. Eye pressures were normal. Then the lights dropped, the lens swung in, and the beam focused directly on the back of her eyes. A healthy optic nerve looks like a neat, well-defined, flat pink doughnut where millions of nerve fibers exit the eye and head toward the brain. Chloe's optic nerves didn't look like doughnuts. In both eyes, the nerve heads were violently swollen, bulging outward into the eye cavity like over-inflated balloons. The crisp borders were completely blurred, the surrounding blood vessels engorged and buried under layers of swelling. Bilateral papilledema. Chloe didn't have a bad pillow, a sleep posture problem, or earbud-induced tinnitus.