The first time I saw Edina, she had just learned two life-changing facts. The first was that the cause of her five years of blindness was cataract, the most common cause of blindness worldwide. The second thing she learned was her condition was treatable, and within 48 hours her sight would be restored. There in the doctor's makeshift examination room in a village in rural Tanzania, unable to see her hands in front of her face – let alone me or the ophthalmologist who was telling her the good news – Edina smiled.