Why do I see stars when I push my eyes?
'Oh, oh, everybody's starry eyed...' when you press down too hard on closed eyelids it can appear as though lights are flashing.
Asked by: Dale Wilkinson, Guildford
Pressure on the eyeball compresses the retinal artery. You don't have to press terribly hard to cut off the blood supply to the retina entirely.
Deprived of oxygen, the photoreceptors can start firing randomly, causing swirling colours or flashing lights. It's a similar phenomenon to the stars you see when you stand up too suddenly.
Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.