If the eye moves, the floaters follow sluggishly, because they are contained in the vitreous humor, which, being gelatinous, is subject to inertia. If the eye stops moving, the floaters settle down. 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 moves, the dots follow instantaneously, because they are contained in the retina. If the eye stops moving, the dots keep darting around. Scheerer's phenomenon consists of corpuscles of identical diameter and visual sharpness, of a simple dot or worm-like shape, brighter than the background. Scheerer's phenomenon can be easily distinguished from floaters ( muscae volitantes). 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 to the perceived entoptic dots.ĭifference from other entoptic phenomena
In a technique known as blue field entoptoscopy, the effect is used to estimate the blood flow in the retinal capillaries. The dots will not appear at the very center of the visual field, because there are no blood vessels in the foveal avascular zone. This behavior of the blood cells in the capillaries of the retina has been directly observed in human subjects by adaptive optics scanning laser ophthalmoscopy, a real time imaging technique for examining retinal blood flow. Red blood cells pile up behind the white blood cell, showing up like a dark tail. The gaps are elongated because a spherical white blood cell is too wide for the capillary. 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 eye and brain "edit out" the shadow lines of the capillaries, partially by dark adaptation of the photoreceptors lying beneath the capillaries. īlue light (optimal wavelength: 430 nm) is absorbed by the red blood cells that fill the capillaries. The dots are white blood cells moving in the capillaries in front of the retina of the eye. Their shadow is the cause of the blue field entoptic phenomenon. Explanation Ophthalmogram showing blood vessels in front of the retina. 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 highly conspicuous against any monochromatic blue background of a wavelength of around 430 nm in place of the sky. 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 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. The dots appear in the central field of view, within 15 degrees from the fixation point. The dots' rate of travel appears to vary in synchrony with the heartbeat: they briefly accelerate at each beat. The dots may appear elongated along the path, like tiny worms. Some of them seem to follow the same path as other dots before them. The dots are short-lived, visible for about one second or less, and traveling short distances along seemingly random, undulating paths. 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. Note the size of the bright dots in relation to the hand. Even in the twentieth century, people were ‘rational’ enough to travel to the moon and back and yet still ‘irrational’ enough to believe in supernatural entities and forces that transcend, and in effect make nonsense of, all the laws of physics on which their moon journey depended.Simulation of the blue field entoptic phenomenon. That duality in human behaviour did not disappear at the end of the Stone Age. The unknown person of Time-Byte I had the rational, ‘scientific’ knowledge and skill to make a tallow lamp and also a set of beliefs that were the imperative for his or her apparently irrational underground journey. “the essence of being human is an uncomfortable duality of ‘rational’ technology and ‘irrational’ belief.
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