See inside your eye Part 2 Using a blue light field to see white blood cells moving on your retina
See inside your eye with that same eye. Part2. Have you ever looked up at a blue sky andseen tiny points of light darting abouté, Although some people refer to these spotsof light as bluesky sprites, prana, vitality globules, or etheric globules, what you arereally seeing is not something etheric but something entoptic (within the eye) causedby white blood cells moving in the capillaries on the surface of your retina. We call thisflying corpuscles or the blue field entoptic phenomenon. We see with the retina which is at the backof the eye, so we can actually see things
on the surface of the eye and inside the eye,as demonstrated in part one of this tutorial series. We can even see things on the verysurface of the retina such as blood vessels and the blood cells moving within them. Iwill review the history and science relating to the blue field entoptic phenomenon andthen show you a number of ways to get truly extraordinary views of these quot;flying corpusclesquot;. Although it had been written about previously,the first person who unambiguously described and investigated the blue field entoptic phenomenonwas the German Johann Steinbuch in 1813. Steinbuch had seen the blood flow incapillaries in the webbed skin of frogs through
a microscope so when he saw specks of lightmoving about while looking at a sunlit white wall he surmised that it was the blood movingthrough the capillaries on his own retina. He wrote that he also saw the phenomenon whilelooking at the blue sky. In 1819, the Czech researcher Johannes Purkinjesuggested exerting yourself and then looking at a bright surface such as a snowfield. Hedrew a simple diagram to show the movement of the blood cells. One century later, a biographerdrew another simple figure in which he added the paths the blood cells seemed to follow.The actual network of capillaries on the retina is much more intricate as this anatomicaldrawing from 1881 shows.
This detailed drawing with exaggerated vesselswas done by William Ayres of his very own capillaries. To see the shadows of thecapillaries on your own retina just poke a hole in a card, then face a bright surfaceand rapidly rotate the hole in front of your eye. Chemists have long used blue cobalt glasswhen doing a flame test, so it isn't surprising that in 1860, chemistry professor Ogden Roodwrote about looking up at the sky through cobalt glass and seeing something quot;resemblinganimalculesquot; which he deduced could be quot;bloodcorpuscles circulating in the retinaquot;.
In 1896, the physiologist George Burch reportedon a potentially better technique, using light with a wavelength between Fraunhofer linesH and G or between about 400 and 430 nanometers. Burch used a prism to get such light, butin 1901, Peter CooperHewitt introduced the first commercial mercury vapor lamp, a muchmore convenient source. In 1907, the eye surgeon E. P. Fortin wrote about using a CooperHewittlamp with a cobalt glass filter to obtain dichromatic light with wavelengths of 400and 430 nanometers. Fortin also built blue field entoptoscopes which used sunlight focusedon filters. The German ophthalmologist Richard Scheereralso developed several devices and, in 1924,
he published a thorough report about the historyand al applications of the phenomenon. While Scheerer presented convincing evidencethat it was indeed blood flow on the retina that was being seen in blue light, he couldn'texplain the phenomenon or even say whether it was caused by red cells (erythrocytes)or white cells (leukocytes). But in 1954, Ursula SchmidtGross publisheda study where people with and without leukemia matched figures on a chart to what they sawwhen they looked at sunlight through a blue filter glass. She showed a correlation betweenthe figures they selected and their white cell count but no correlation with their redcell count, proving the blue field entoptic