A closer look

Sometimes fixing a neurological glitch just requires putting a sticker on your glasses. When a stroke or nerve palsy causes sudden diplopia (double vision), your eyes essentially divorce and look in different directions. Instead of immediate surgery, doctors slap a Fresnel prism—a thin, grooved sheet of PVC—onto the patient's existing glasses. It bends the incoming light to match the misaligned eye, instantly hacking the brain's visual cortex back into single vision.