The shout test
I know its not on the syllabus but correction of long and short sight by lenses is something that a lot of students can relate to. I always like to illustrate my explanation with a couple of drawings showing people wearing glasses to correct their vision. Short sighted people have concave lenses that make their eyes (and the rest of their face) look small giving them that far away look, they're probably wondering why people always shout at them. The far away look is actually just an illusion since the image through the lens is closer then the face. Long sighted people have convex lenses which magnify the eyes causing people to step away. So if you are always being shouted at your probably short sighted but if you have to shout because people are so far from you then you are long sighted.