So, I spend a lot of time drawing. When I hit my late teens/early 20's, I noticed that when I looked up after about three hours of drawing, my vision was fuzzy for the rest of the day (like, I was seeing colored blobs; that bad). It really scared me. Now it's gotten worse, to the point that a mere half an hour of drawing leaves my vision blurry for the rest of the day, even when using reading glasses. Is this presbyopia? Or something else? The web keeps saying that you shouldn't even have this until you're in your 30's, and the last thing I want to lose is my vision. It's hard to draw if you can't see. Anybody with experience and/or knowledge?