Henry 'Indiana' Jones Jr. sometimes needs to wear glasses but most of the time doesn't seem to need them. Are they prescription? Are they needed for reading (inconsistently)? Is he trying to look smarter than he is?
In Raiders of the Lost Ark he seems to wear them while at the university but not later.
In Temple of Doom he seems to only wear them when he is at dinner. Probably the one time he wants to not see what is right in front of him.
In The Last Crusade he isn't wearing them when talking to Marcus. Then he puts them on to examine the Grail Tablet (but not before when looking at other things, like the painting of the knight holding the cup).
However throughout most of the movie he can easily read the Grail Journal without glasses.
I am sure there are other examples with him having glasses and other examples of him reading without them.