A healthy woman arrived at an emergency department with blurred vision and a hazy cornea that had come on within hours of gardening. She wore contact lenses. The workup found nothing alarming, and she was sent home with a diagnosis of conjunctivitis.
She came back worse. By then her vision had fallen to detecting motion. Only when clinicians pressed harder on her exposure history did the answer surface. She had been handling butterfly milkweed, Asclepias tuberosa, a plant sold in American garden centers specifically because monarch butterflies depend on it.
