Probably way too much,* by the standards of Oxford physics professor Josh Silver, who has developed a wearer-adjustable set of eyeglasses that use water-filled plastic bags as lenses. They’re so cheap that they can be distributed freely in underdeveloped and impoverished communities, which is exactly what Silver is doing, to the tune of 30,000 units so far. No visit to the optometrist and no custom lens grinding, just a standard pair of specs that you adjust once to your own visual comfort, using a small syringe, and then seal shut. A nice reminder that Making isn’t just about scaring away impressing potential mates with your flatulence-tweeting office chair. link

*In all fairness to the noble discipline of optometry, if you are able to visit a proper eye-doctor you probably should. Silver’s lenses can only correct for spherical, not cylindrical, defects in the eye, which is to say that if you have an astigmatism (as 1 in 3 adults does, per one study) you still need traditional lenses for full correction.