I know this is picky, but here goes. Jack diagnoses Sawyer with hyperopia in Episode 19 (Dues Ex Machina). The symptoms and diagnois are valid. At one point Sawyer tries on different pairs of glasses, he says that one pair makes it worse - again this makes sense because he was trying on glasses for myopia (near-sightedness) which would, indeed, make it worse. But when Sayid fabricated a pair of glasses from the wreckage he made them out of near-sighted glasses. You can see this when you look through the corners of Salyer's glasses - near-sighted glasses make things in the background look slightly smaller - far-sighted glasses would make things in the background look very distorted / blurry. I know most people would never notice this, but as an eye doctor it is something that should have een caught.