Oh wow, this made me realize something I've had for 20 years: When I look too close for a few seconds, I get blurriness at the center of my vision. It goes away after a while, but this made me realize that the blurry region is actually my fovea!

I have no idea why my fovea blurs when I look close up at something, and doctors haven't been able to figure it out, but at least now I can google it better.