The problem with contact lenses is that you just can't sleep whenever you want to, and there's nothing as good as falling asleep in the afternoon. So Joao sticks with the spectacles. Of course, the best bet is to get light sensitive lenses- otherwise the only option is prescription sunglasses and you have to carry a pair of plan spectacles as well, for when you go indoors (unless you want to look like Roy Orbison).
In fantasy world Joao would have 20:20 vision and just pop on a pair of sun glasses whenever the fancy took him.Look at this Ray Ban ad from 1979- they reckon everybody needs six differebnt types of 'sunglass'... well, they would, wouldn't they? 
Remember Richard Davalos in Cool Hand Luke? Loved those glasses.
