This question is on behalf of a friend. Why is it, when you close your eyes and press on your eye ball, after some time you get white blotches appear, but there are no visible light waves entering the pupil ?

When light enters your eye, it hits photoreceptors called rod and cone cells on your retina which contain light sensitive pigments (rhodopsin and iodopsin) that break down when exposed to light. When this happens it create an impulse to the sensory areas of the brain allowing you to see.

 

When you press on your eyeball, the pressure has basically the same effect as light and breaks down the pigment to send impulses to the brain as if it were light.

Thanks for the response Aj47, I'll send a link to my mate.