I guess it's more the other way around. IF you require/prefer/want sunglasses, they need to be of the "prescription" type. But if you don't want to wear sunglasses you will obviously wear your own, normal, non-tinted glasses. Plenty of pilots fly around with just their normal glasses and don't use sunglasses.
So if you don't normally use sunglasses and you don't intend to use sunglasses in aviation, don't worry.
Having said that, when you are flying you tend to be well above ground level (duh!). This means that the dark objects, like houses, trees and whatnot, that are normally at eye level and reduce the average amount of light that hits your eyes, are not there. So the average amount of light that enters your eyes is higher, and you might need sunglasses earlier.
Furthermore, certain types of sunglasses enhance contrast, which is useful on an overcast day. And there are pilots who make a point of wearing sunglasses as protection against the effects of a birdstrike on the canopy.
On the con side, any type of glasses will restrict your peripheral vision a bit, and obviously dirt on the glasses even more so. That may mean you detect a potential conflict with another aircraft later, or not at all. But this holds true for regular and sunglasses.
Edited to add that your medical will specify something along the lines of "must wear glasses and carry a spare set of glasses". So you'll need spares somehow in any case.
Last edited by BackPacker; 7th Mar 2013 at 14:37.