"Say cheese!" Is a common phrase used right before a big flash leaving your vision compromised for a few seconds. Keeping your eyes open during a pop of bright light is difficult, which is probably why so many blink when a picture is taken. But why is it that one flash of light from a tiny camera can leave us cringing and rubbing our eyes? It all starts with understanding basic eye anatomy.
Purpose of the Retina
The retina is a part of the eye that cannot be seen from the outside. It lies against the back wall of the eyeball and is a thin layer of nerve tissue. The purpose of the retina is to interpret light and images into electrical signals. These signals enter our brains and are then interpreted into images. Without the retina we would be unable to interpret what we are seeing.
During a Flash of Light
When your eyelids don't protect us and a flash of light is unavoidable then often you will see spots or ghost like dots floating across your vision. They often will take a few seconds to go away and will not disappear instantly even with closing the eyelid. What has happened is the intense light has overstimulated the retina. The result is poor vision or a dark afterimage until the retina recovers.
Once a flash of light has pushed the retina to its maximum, the cells are still responding as the brain is simultaneously seeing images. The retinas are not reacting as well to the normal light in the environment since they have been desensitised from the bright flash of light. The brain function and the retina reaction are both acting at once, which causes in overlap of spotty or blurred vision and the images your brain is seeing. Once the retinas adjust from being overstimulated, the images being seen by the brain will appear without dark spots.
The occasional flash of light from a camera or other small device may be uncomfortable but will not do permanent damage. Overexposure to some sources of light, however, may be harmful. This is why it's not good to stare at the sun. A small accidental glimpse isn't anything to stress over, but continually staring would do some damage to the visual cells. This will cause a blind spot in your vision called solar retinopathy that can be permanent. It is important to protect your eyes from bright lights when possible by using sunglasses and other eye protective wear to maintain healthy vision.