Blue field entoptic phenomenon

The blue field entoptic phenomenon or Scheerer’s
phenomenon is the appearance of tiny bright dots moving quickly along squiggly lines in
the visual field, especially when looking into bright blue light such as the sky. The dots are short-lived, visible for a second
or less, and traveling short distances along seemingly random, curvy paths. Some of them follow the same path as predecessors. The dots may be elongated along the path like
tiny worms. The dots appear in the central field of view,
within 10 to 15 degrees from the fixation point. The left and right eye see different dots;
someone looking with both eyes sees a mixture. Most people are able to see this phenomenon. However, it is rather weak, and many people
don’t notice it until asked to pay attention. Explanation The dots are white blood cells moving in the
capillaries in front of the retina of the eye. Blue light 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 much rarer
than the red ones 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
leukocyte is too wide for the capillary. Red blood cells pile up behind the leukocyte,
showing up like a dark tail. This behavior of the blood cells in the capillaries
of the retina has been observed directly in human subjects by adaptive optics scanning
laser ophthalmoscopy, a real time imaging technique for examining retinal blood flow. The dots won’t appear at the very centre
of the visual field, because there are no blood vessels there. Blue field entoptoscopy
In a technique known as blue field entoptoscopy, the effect is used to estimate the blood flow
in the retinal capillaries. The patient is alternatingly shown blue light
and a computer generated picture of moving dots; by adjusting the speed and density of
these dots, the patient tries to match the computer generated picture as well as possible
to the perceived entoptic dots. Difference from other entoptic phenomena
Scheerer’s phenomenon can be easily distinguished from floaters. Scheerer’s phenomenon consists of corpuscles
of identical diameter and visual sharpness, of a simple dot or worm-like shape, brighter
than the background. If the eye stops moving, the dots keep darting
around. If the eye moves, the dots follow instantaneously,
because they are contained in the retina. In contrast, floaters are specks or threads
of variable diameter and variable visual sharpness, some of complex shape, darker than the background. If the eye stops moving, the floaters settle
down. If the eye moves, the floaters follow sluggishly,
because they are contained in the vitreous humor which is subject to inertia. There are also several phosphenes that need
to be distinguished from Scheerer’s phenomenon. See also
Floater References External links
Video describing history and science of blue field entoptic phenomenon and viewing techniques