Ogden Rood

Transcription

See inside your eye with that same eye. Part 2. Have you ever looked up at a blue sky and seen tiny points of light darting about?, Although some people refer to these spots of light as blue-sky sprites, prana, vitality globules, or etheric globules, what you are really seeing is not something etheric but something entoptic (within the eye) caused by white blood cells moving in the capillaries on the surface of your retina. We call this flying corpuscles or the blue field entoptic phenomenon. We see with the retina which is at the back of 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 video series. We can even see things on the very surface of the retina such as blood vessels and the blood cells moving within them. I will review the history and science relating to the blue field entoptic phenomenon and then show you a number of ways to get truly extraordinary views of these "flying corpuscles". Although it had been written about previously, the first person who unambiguously described and investigated the blue field entoptic phenomenon was the German doctor Johann Steinbuch in 1813. Steinbuch had seen the blood flow in capillaries in the webbed skin of frogs through a microscope so when he saw specks of light moving about while looking at a sunlit white wall he surmised that it was the blood moving through the capillaries on his own retina. He wrote that he also saw the phenomenon while looking at the blue sky. In 1819, the Czech researcher Johannes Purkinje suggested exerting yourself and then looking at a bright surface such as a snowfield. He drew a simple diagram to show the movement of the blood cells. One century later, a biographer drew 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 anatomical drawing from 1881 shows. This detailed drawing with exaggerated vessels was done by Doctor William Ayres of his very own capillaries. To see the shadows of the capillaries on your own retina just poke a hole in a card, then face a bright surface and rapidly rotate the hole in front of your eye. Chemists have long used blue cobalt glass when doing a flame test, so it isn't surprising that in 1860, chemistry professor Ogden Rood wrote about looking up at the sky through cobalt glass and seeing something "resembling animalcules" which he deduced could be "blood-corpuscles circulating in the retina". In 1896, the physiologist George Burch reported on a potentially better technique, using light with a wavelength between Fraunhofer lines H and G or between about 400 and 430 nanometers. Burch used a prism to get such light, but in 1901, Peter Cooper-Hewitt introduced the first commercial mercury vapor lamp, a much more convenient source. In 1907, the eye surgeon E. P. Fortin wrote about using a Cooper-Hewitt lamp with a cobalt glass filter to obtain dichromatic light with wavelengths of 400 and 430 nanometers. Fortin also built blue field entoptoscopes which used sunlight focused on filters. The German ophthalmologist Richard Scheerer also developed several devices and, in 1924, he published a thorough report about the history and clinical applications of the phenomenon. While Scheerer presented convincing evidence that it was indeed blood flow on the retina that was being seen in blue light, he couldn't explain the phenomenon or even say whether it was caused by red cells (erythrocytes) or white cells (leukocytes). But in 1954, Ursula Schmidt-Gross published a study where people with and without leukemia matched figures on a chart to what they saw when they looked at sunlight through a blue filter glass. She showed a correlation between the figures they selected and their white cell count but no correlation with their red cell count, proving the blue field entoptic phenomenon is related to white blood cells. Schmidt-Gross improved on her experimental technique with a xenon lamp and a movable display. Today, blue field entoptoscopes using bandpass interference filters in place of glass filters can be found in science museums and they have also been combined with computer controlled video displays to allow research subjects and patients to accurately report on such things as the number, general location, and speed of the corpuscles. We now know quite a bit more about the details of what makes the blue field entoptic phenomenon. White blood cells are larger and far less numerous than red cells. They deform to fit in the capillaries and flow more slowly so that red cells pile up behind and a space opens up in front. Red cells contain hemoglobin. This graph shows the relative absorption of light of different wavelengths by hemoglobin saturated with oxygen (oxyhemoglobin) and desaturated hemoglobin (deoxyhemoglobin). Combining these two gives us an idea of the wavelength of light we need to have, somewhere between about 400 and 440 nanometers which would appear violet to blue to our eyes. Red cells absorb this light whereas the plasma and white cells do not so if the retina is illuminated by blue-violet light we see a short streak of light followed by a dark tail as a white cell moves through a capillary. Sunlight has all the wavelengths of light visible to our eyes, which is why Steinbuch could see flying corpuscles while looking at a sunlit white wall. You can simulate this nicely by shining an LED light through several layers of a white disposable plastic grocery bag. Keep in mind that you will not see flying corpuscles in the very center of your vision as there are no capillaries there. You have to look straight ahead while being consciously aware of your peripheral vision. Also, be aware that long-term exposure to high intensity light, especially blue light, can damage your eye. In 1979, the Swiss biophysicist Charles Riva, investigated the level of blue light intensity needed to see the corpuscles fly and determined that it was about 1000 times lower than a harmful level. He advised that the light level be gradually increased, allowing time for the eye to adapt, until the phenomenon could be seen. As Steinbuch noted back in 1813, the blue sky can be better than white sunlight. This is because, although dimmer, this diffuse blue light has a higher percentage of wavelengths in the absorption range of hemoglobin. Looking at the sky through cobalt glass, as Rood described in 1860, results in light which is dimmer still but even more concentrated in suitable wavelengths. You can easily obtain several small pieces of this blue glass from a stained glass studio and try this yourself. However, it is much better to use a couple thickness of cobalt glass with a modern LED light, topped by one or two layers of a plastic bag to limit and diffuse the light. Now you will have a nice, bright blue field and you will see the flying corpuscles much clearer. The ultimate filter is a modern bandpass interference filter where all the light leaving falls within a narrow range that is highly absorbed by hemoglobin. I used a 420 nanometer filter in this entoptoscope I built with an LED AA Maglite and a 3/4-inch copper coupler. With it, I can see a swirling mass of light worms with dark tails following definite paths and moving in time with my pulse, definitely a better view than with cobalt glass. But an LED can do the same for far less money. I used a Roithner Lasertechnik model LED420-01 as a direct replacement for the bulb in an incandescent AA Maglite. Be sure you get the insertion direction right and then add an extension and some plastic to diffuse and limit the light. In general, entoptic phenomena are not much used in clinical medicine because of the need to rely on a patient's subjective reporting, and because other, better methods are usually available for evaluation of the eye. However, use of the blue field entoptic phenomenon has been suggested for self-monitoring of white blood cell levels and assessing the functioning of the retina. Researchers have also used it to study blood flow in the retina. See the following articles, books and websites for more information. Click on like and be sure to subscribe for future videos on seeing inside your eye with that same eye.