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 short-lived, visible for about one second or less, and traveling short distances along seemingly random, undulating paths. Some of them seem to follow the same path as other dots before them. The dots may appear elongated along the path, like tiny worms. The dots' rate of travel appears to vary in synchrony with the heartbeat: they briefly accelerate at each beat. The dots appear in the central field of view, within 15 degrees from the fixation point. The left and right eye see different, seemingly random, dot patterns; a person viewing through both eyes sees a combination of both left and right visual field disturbances. Most people are able to see this phenomenon in the sky, although it is relatively weak in most instances; many will not notice it until asked to pay attention. The dots are highly conspicuous against any monochromatic blue background of a wavelength of around 430 nm in place of the sky. The phenomenon is also known as Scheerer's phenomenon, after the German ophthalmologist Richard Scheerer, who first drew clinical attention to it in 1924. The dots are white blood cells moving in the capillaries in front of the retina of the eye. Blue light (optimal wavelength: 430 nm) is absorbed by the red blood cells that fill the capillaries. The eye and brain "edit out" the shadow lines of the capillaries, partially by dark adaptation of the photoreceptors lying beneath the capillaries. The white blood cells, which are larger than red blood cells, but much rarer and do not absorb blue light, create gaps in the blood column, and these gaps appear as bright dots. The gaps are elongated because a spherical white blood cell is too wide for the capillary. Red blood cells pile up behind the white blood cell, showing up like a dark tail.