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 blue light (such as the sky). <ref>Scheerer R., "Die entoptische Sichtbarkeit der Blutbewegungen im Auge und ihre klinische Bedeutung." Klinisches Monatsblatt Augenheilkunde 1924;73:67-107 (German) </ref> These dots are due to the white blood cellsthat move in the capillariesin front of the retinaof the eye, near the macula. <ref> Sinclair et al. "Investigation of the source of the blue field entoptic phenomenon." Investigative Ophthalmology & Visual Science. April 1989;30(4):668-673. PMID 2703307 </ref> The dots move somewhat in sync with the heart beat.

Blue light (optimal wavelength: 430 nm) is well absorbed by the red blood cellsthat fill the capillaries. The brain "edits out" the dark lines that would result from this absorption. The white blood cells, which are much rarer than the red ones and do not absorb the blue light well, create gaps in the blood column, and these gaps appear as bright dots.

In a technique known as blue field entoptoscopy, the effect is used to measure the blood flow in the retinal capillaries, which is important in diseases such as diabetes. The patient is alternatingly shown blue light and a computer generated picture of moving dots; by adjusting the speed and density of the computer generated dots, the patient tries to match the computer generated picture as best as possible to the perceived entoptic dots. This then allows calculation of the blood flow in the capillaries.

Scheerer's phenomenon should not be confused with "floaters" or muscae volitantes. Scheerer's phenomenon is distinguished by the appearance of multiple, identical-looking bright dots that follow each other rapidly along the same path. Floaters are variable in appearance; although they sometimes are dots, they often have the appearance of threads or shreds of crumpled cellophane. Floaters remain almost stationary or drift slowly and do not follow well-defined paths. They are due to debris floating in the vitreous humorof the eye.

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It uses material from the http://en.wikipedia.org/wiki/Blue+field+entoptic+phenomenon Wikipedia article Blue field entoptic phenomenon.