In a paper published in March in the journal Optometry and Vision Science, four researchers compare the full costs of delivering used glasses to the costs of instead delivering ready-made glasses in standard powers. The authors find that recycled glasses cost nearly twice as much per usable pair.

Using labor costs based on wage rates in Australia, where the research was done, the cost of delivering a pair of ready- made glasses is $11.28 (in U.S. dollars) for lower powers requiring only a visual inspection and $13.23 if the lens power is checked with a focimeter, a tabletop instrument that looks something like a microscope.

Because recycled glasses require more labor-intensive screening and have a high rejection rate, each pair winds up costing a lot more than a ready-made pair: $20.49 for the 7 percent survival rate and $17.86 at a more optimistic 11 percent rate.