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The entoptic phenomenon (or Scheerer's phenomenon and sometimes referred to as the entopic phenomenon which is a common spelling mistake) is when one can actually visualise blood flow through the retinal blood vessels. We all have the potential to see the blood flow but most of us are able to ignore this. Some people may become suddenly aware of this and this sudden awareness may lead to the idea that there is a problem with the eyes, when actually there is not. This moving dots effect are actually leukocytes, or white blood cells (WBC), which move along through the blood-filled capillaries.

There are many capillaries on the retina which have the shape of a snake, a sine-wave, and when a leukocyte travels through that channel, it executes a sinusoidal "wiggle" motion. The capillaries are said to be normally invisible because they are full of hemocytes (red blood cells), and these hemocytes are too close to each other, and too far away from the retina to create individual moving shadows. Therefore, like the capillaries themselves, our retinas "edit" the blood cells out the view perceived by our brains. On the other hand, the leukocytes (White blood cells) are large, and they act like gaps in the columns of blood which fill the capillaries. These "moving holes" in the blood are made visible whenever we stare at a uniformly illuminated surface.

The entoptic phenomenon can be seen especially observed when looking at a bright blue sky. Small, rapid pin-point sparks of light can be seen darting about in the central vision. Some people may think that these sparks are floaters. In reality, they represent white blood cells moving through the blood capillaries of the retina. This is a normal finding, and actually may indicate normal retinal function.

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