Some days I see distant objects more sharply through my new glasses than with my naked eyes and other days it is the other way around. (i've been wearing glasses for about eight years). When I first noticed it I thought that my optometrist had made a mistake in his prescription, but then I realized the problem was my eyes.

In a chat on the phone the optometrist suggested it might be due to a diabetic condition but I am pretty certain I am not diabetic. Does anyone have any thoughts on possible causes?