You settle in for bed. You close your eyes and right before you fall asleep, you notice something; a twinkling, swirling pattern of stars and colors producing a make-shift light show on the inside of your closed eyelids.
Many people who have seen this visual phenomenon think it is an light-induced afterimage of what they had seen before they closed their eyes but an afterimage may only be part of what they are seeing. The real reason we are treated to this fuzzy fireworks display behind closed lids has to do with phosphenes! Phosphenes are the moving visual sensations of stars and patterns we see when we close our eyes. They are thought to be caused by the inherent electrical charges the retina produces even when it is in its "resting state" and not taking in a ton of information and light like it does when our eyes are open.
One can relate this analogy to an old fashioned television set. When its on and on the right channel, you see colors, pictures and images similar to what our retinas allow us to see when our eyes are open. However, unlike a TV set, our retinas can not be turned off. Even when we close our eyes, they are active. They are buzzing with the metabolism and regeneration of visual pigments. You can think of it as the TV not being shut off, but changed to a fuzzy picture like when an old TV is on but in between channels. Phosphenes are like visual noise that our retinas make.
Phosphenes can also be caused by mechanical stimulation of the retina through applied pressure or tension. The physical pressure being put on the retina stimulates it and generates phosphenes and light. You can test this by closing your eyes and gently pushing on your eye. Be careful not to do this too much or too hard as it can harm your eyes if you are too rough or do this too frequently but if we test this just for a few seconds with a gentle push, you will be able to see how physical pressure can stimulate the retina and cause it to see light that "isn't there."
(Just so you know, if you are seeing flashes of light in your everyday life even without pushing on the eye, contact your eye doctor. Tension or pulling on the retina, like that which happens when the eye is experiencing retinal tension, a tear or detachment can cause flashes. Retinal tears and retinal detachments are sight threatening conditions that need to be evaluated promptly by your eye doctor and repaired in order to preserve vision in the affected eye.)
Hope you enjoyed this Vision Tip of the Week and you now understand why when you close your eyes you may be treated to a starry, starry night.