I was just talking about drawing glasses and how eyes look behind them and decided to do a sketchy diagram. I am drawing with my finger so the pictures are a bit wobbly….
When you draw the eye behind the glasses, always look to see if the face and eye look bigger or smaller. You can tell if they are long sighted (bigger) or short sighted (smaller). It makes it more realistic if you notice this sort of thing. If the eyes are the same as normal it means the glass is flat in the lens, not curved!
There is a film staring James Stewart called flight of the phoenix. One of the characters wears glasses. But the lenses are flat and the light glints off them like window panes!