Blue field entoptic phenomenon

The blue field entoptic phenomenon is an entoptic phenomenon characterized by the appearance of tiny bright dots (nicknamed blue-sky sprites) moving quickly along undulating pathways in the visual field, especially when looking into bright blue light such as the sky. The dots are an optical illusion resulting from larger white blood cells displacing smaller blue light-absorbing red blood cells, as they flow in the capillaries in front of the retina of the eye, The dots are short-lived, visible for about one second or less, and travel short distances along seemingly random, undulating paths.

Source: Wikipedia — Blue field entoptic phenomenon (CC BY-SA 4.0)