What you are experiencing is called entoptic phenomenon. These are images whose source is actually inside the eye itself. There are different manifestations of entoptical effects, depending on how they are generated. Blue field entoptic phenomenon looks like tiny bright dots, or bugs, moving along a wiggley racetrack. These are easier to see when looking at a uniformly lit area such as the blue sky, an illuminated wall in your home or a field of pure blue light. What you are actually seeing in this case are white blood cells racing through the capillaries in front of the macula, or central part, of your retina.
The Purkinje tree is another example of an entoptic phenomenon. This is an image of your blood vessels, located above the retinal photoreceptors, inside your eye. It is best seen by shining a small bright light against your closed eyelids, against your eyeball, or obliquely through your pupil, and wiggling the light quickly back and forth. You may have experienced this image when being examined by your ophthalmologist with the bright light she has on her head. You don't normally see this image as your retina is adapted to the shadow they cast however, when you shine the light from the side, the adaptation is defeated and you see the vessels.
Does this make sense to you?
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Dr. Rick MD FACS