Look up at a bright, blue sky and you may notice tiny dots of moving light. You aren’t imagining these spots. They are created by your own white blood cells flowing through your eyes. What you are experiencing is a very normal occurrence called the blue field entoptic phenomenon.
By Unmismoobjetivo – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=27269687