Question: What is the ruling on wearing Sunglasses?
Answer: I do not see [ie. the benefit] of Sunglasses, except for a person whose eyes are in need of them. As for other than that type of person, then it is a mistake because he will not be able to endure looking at the sun afterwards except with sunglasses. Try not to wear glasses, not sunglasses or other than it, except if the eyes need, where that if you abandon sunglasses your eyes will shed tears and overheat. In this case there is no problem.
There are very old men that look at the Crescent moon and the youth who have sunglasses can not see it. However, the eye that sees is like the body. If you notice them [the eyes] tired from reading or staring at something, then stop. Just as if you are lazy [ie. from walking] then stop walking. It [the eyes] are a muscle from the muscles.
[Taken from Liqaa ul-Baab ul-Maftooh no. 220 found here:
Faisal ibn Abdul Qaadir ibn Hassan