when i close my left eye with my hand, everything looks a shade or two darker. i have asigmatism in that eye and my vision is not good. when i open my left eye, i can see everything a bit lighter. my vision has not changed sinse i noticed this. i may have had it forever just never noticed it. what may this be. my eye does not hurt or anything and my vision with both eyes open is perfect with glasses and i dont notice difference. its only when i cover my left eye and then open my left eye and do it again. what do you think this is. i dont think its serious, but i just want to know.