I would be curious though as to how evolution works when a specific sense organ begins to weaken in every subsequent generation but however due to human beings ingenuity, the impact from the weakening may not be fatal.
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.
There are plenty of examples of characteristics that actually make individuals less likely to survive, but flourish because they also make the individual a more attractive breeding partner--the peacock's cumbersome tail, for example, which is used in mating displays.
Currently the only significant evolution in the human population is for the non use of birth control.