NO PRESCRIPTION IS NECESSARY FOR A SPECIAL PAIR of eyeglasses called Adspecs. Their sturdy plastic frames encase flexible, oil-filled membranes that change the refractive power of the lens as the wearer pumps oil in or out with a syringe. Pumping oil out draws the membranes together, curving the lens inward and correcting for nearsightedness. When oil is pumped in, the membranes (and lens) bow outward, improving close-range vision. Manufactured for around $19 a pair, Adspecs—short for adaptive spectacles—are a boon in places like sub-Saharan Africa, where there is one optometrist for every million people. With Adspecs, wearers need only an eye chart to fine-tune their vision.