Sudden changes in light intensity do not harm the eye under normal conditions, as the brain automatically directs the gaze away from the light source itself.
If it weren’t like this, you could go blind just by opening your eyes in the morning.
However, the sunlight is powerful enough to destroy the nerve cells in the retina if the light shines directly into the eye for some time.
Ultraviolet rays damage the retina
Then the ultraviolet rays of the sunlight affect the retina and it produces too many messengers. The messengers can damage the light-sensitive cells inside the eye, causing permanent damage or blindness. The sunlight often causes eye damage when people watch an eclipse without protective glasses.
A short but powerful flash of light, for example from a grenade or a weak laser beam, can cause temporary vision loss, which usually recovers in less than ten minutes.
The eye protects itself
Too much light can damage the cells inside the eye, but usually the eye adapts to the light influx very quickly and the vision is not damaged.
When light falls on the eye, it is refracted in the cornea, which directs the light into the eye.
The iris is a sphincter that controls the size of the aperture and thus the amount of light entering the eye.
The pupil contracts and lets only a small amount of strong light in so that the retina, at the back of the eye, is not damaged.
The retina contains light-sensitive neurons. If too much light gets in, too many messengers are released and they can damage your vision.
