I love elegant diagnostics and I was pretty impressed with the effectiveness of this. I took my glasses off to check and BAM - there's Marilyn. Nothing wrong with glasses folks! Go get them if you're squinting! :-)
"You probably know whether or not you're near-sighted, but some people get so used to seeing things a certain way that they ignore a vision problem, squint a lot, and end up with unnecessary eye strain at the computer. The double-image above cuts straight to the point: If you see Albert Einstein while sitting a normal distance from your computer, you're seeing things as you should. If you see Marilyn Monroe, you should probably be wearing glasses or contacts."