When gazing at a bright, clear blue sky, many people observe tiny, moving dots or sparkles in their vision. This common visual experience is not an illusion, but rather a normal physiological phenomenon. This article explains what these sparkles are and why we see them.
Describing the Sky Sparkles
These sparkles typically appear as small, bright, white, or clear points of light. They move quickly, often darting across the visual field along seemingly random, undulating paths. This phenomenon originates from within the eye itself, rather than from external sources. They are always present but become most noticeable against a uniform, bright background, particularly a clear blue sky.
The dots are short-lived, usually visible for about one second or less, and travel short distances. Their speed can even vary in synchrony with your heartbeat, briefly accelerating with each pulse. These internal visual events are distinct from other common eye phenomena like “floaters,” which are typically darker and drift more slowly.
Understanding the Cause
The primary scientific explanation for seeing these sparkles is the Blue Field Entoptic Phenomenon, also called Scheerer’s phenomenon. These “sparkles” are actually your own white blood cells, or leukocytes, moving through the capillaries located on the surface of your retina. The retina is the light-sensitive tissue at the back of your eye that receives light and converts it into signals for the brain.
Blood flows through tiny vessels, called capillaries, that cross over the retina. Red blood cells, which constitute over 90% of your blood, absorb blue light very effectively. However, white blood cells are larger and much less numerous than red blood cells, and they do not absorb blue light. As these white blood cells pass through the capillaries, they briefly create a “gap” in the column of red blood cells, allowing blue light to pass through to the photoreceptors.
The brain interprets this momentary increase in brightness as a tiny, moving bright spot or sparkle. The white blood cells are often wider than the capillaries, causing them to deform and create an elongated gap, which can make the dots appear somewhat worm-like. Red blood cells can also pile up behind the slower-moving white blood cells, sometimes causing a dark tail to appear with the bright dot. This phenomenon is most striking against a bright blue sky because the blue light is scattered by the red blood cells, making the contrast with the “gap” created by the white blood cells more prominent.
When to Consult a Doctor
The Blue Field Entoptic Phenomenon is a normal and harmless visual experience, indicating healthy blood flow within your retina. There is generally no need for concern if you observe these specific bright, rapidly moving dots. However, it is important to distinguish this normal occurrence from other visual disturbances that may signal a more serious underlying eye condition.
You should seek medical attention if you experience different types of visual symptoms, such as:
A sudden onset or significant increase in floaters (darker spots, specks, or squiggly lines that drift slowly)
Flashes of light (lightning streaks or camera flashes, particularly in your peripheral vision)
A shadow or “curtain” appearing over part of your vision
Blurred vision
A sudden loss of peripheral vision
These symptoms could indicate conditions such as a retinal tear or detachment, which require timely treatment to prevent permanent vision loss.