The fact that we can get around vision problems using technology is precisely what allows such vision problems to become widespread. Poor eyesight has gone fro

The fact that we can get around vision problems using technology is precisely what allows such vision problems to become widespread. Poor eyesight has gone from being massively deleterious and thus exerting a strongly negative selective pressure, to being (usually) trivially correctable and thus having no bearing on natural selection at all (excluding sexual selection). Once you remove selection from the equation, genetic drift gets free reign; suboptimal alleles will spread through the population. Note, however, that in the case of myopia we may well be dealing with a non-heritable environmental effect.