If you go out on a clear day and stare into the azure sky, you might experience some odd visual effects. For example, staring into the sun will cause blind spots in front of your eyes. Under certain light conditions you can even experience “blue field entoptic phenomenon”.
During this kind of entoptic phenomenon you might see tiny bright dots moving in front of your eyes. These moving dots are actually white blood cells in your eyes. They are flowing in the capillaries in front of your eye’s retina.
These blood cells can’t absorb the bright blue light, which creates gaps in the blood column. Later these gaps appear like elongated moving bright dots to your eye sight.
This disorder is also called “Scheerer’s phenomenon”. It’s not dangerous at all and is in fact very common, but most people don’t even notice it if they’re not paying attention to it. You’ve probably experienced it numerous times without realising.