When a person notices small, rapidly moving dots in their field of vision, particularly when looking at a bright, uniform surface, they are experiencing a common physiological event. This visual experience, often presenting as tiny, bright specks, has a benign explanation rooted in the normal function of the eye’s internal structures. It is important, however, to distinguish this harmless phenomenon from other visual disturbances that can indicate a serious underlying health issue.
The Blue Field Entoptic Phenomenon
The perception of bright, quickly darting specks, especially against a bright blue sky, is scientifically known as the Blue Field Entoptic Phenomenon (BFEP). This harmless visual effect is caused by the movement of the observer’s own white blood cells within the capillaries of the retina. Red blood cells, which are the majority of circulating blood, efficiently absorb blue light, casting a shadow on the photoreceptors beneath them.
White blood cells (leukocytes) are less numerous and larger than red blood cells. When a white blood cell travels through a narrow retinal capillary, it creates a temporary, clear gap in the column of red blood cells, allowing a momentary surge of light to reach the photoreceptors. The brain interprets this intense pulse of light as a bright, moving dot that follows the course of the capillaries. This phenomenon is considered a sign of a healthy visual system.
Related Harmless Visual Artifacts
While the BFEP is characterized by bright, fast-moving dots, other common visual disturbances are often confused with it. Floaters, or muscae volitantes, appear as dark, shadowy specks, threads, or cobwebs that drift slowly across the field of vision.
Floaters are caused by cellular debris, protein clumps, or tissue remnants suspended in the vitreous humor, the gel-like substance filling the eyeball. Because the vitreous is gelatinous, floaters follow eye movements sluggishly, unlike the instantaneous movement of BFEP dots. Floaters cast shadows onto the retina, making them appear dark, whereas BFEP dots appear bright due to increased light transmission.
Another type of light sensation is phosphenes, which are distinct from the blue dots. Phosphenes are flashes of light or colored spots that occur without any external light source. These sensations are usually triggered by mechanical stimulation, such as rubbing the eyes or sudden head movement, which causes pressure on the retina and excites the photoreceptor cells.
Pathological Causes of Colored Spots
Though the tiny blue dots are harmless, persistent or sudden flashes of light can signal a medical issue. One common cause is the visual aura that often precedes an ocular migraine. This neurological event is characterized by a temporary visual disturbance called a scintillating scotoma, which typically appears as shimmering, expanding zigzag lines or arcs of light.
Unlike the retinal-based BFEP, the migraine aura originates in the visual cortex of the brain and usually lasts between 10 and 30 minutes. The flashes associated with a migraine are often larger, more patterned, and may involve a temporary loss of part of the visual field. These visual patterns are caused by abnormal electrical activity spreading across the surface of the brain.
A serious cause of colored spots or flashes is photopsia, which results from mechanical stimulation of the retina. As the vitreous humor ages, it shrinks and liquefies, which can cause it to pull away from the retina in a posterior vitreous detachment. This tugging action on the retina generates electrical signals that the brain interprets as flashes of light, often described as lightning streaks.
If the vitreous tugs too forcefully, it can tear the retina, which is a precursor to retinal detachment. Retinal detachment is a separation of the retina from its underlying support layers and requires immediate medical attention.
Warning Signs and Seeking Medical Care
The bright, fleeting dots of the Blue Field Entoptic Phenomenon are a normal part of eye function and require no concern. However, any sudden change in vision warrants an immediate evaluation by an eye care professional. Urgent medical attention is necessary if the visual spots are accompanied by a sudden, significant increase in the number of dark floaters.
A sudden onset of persistent flashes of light (photopsia), especially in the peripheral vision, is a serious warning sign. These symptoms can indicate a retinal tear or detachment, which is a sight-threatening condition. If a shadow or a dark curtain moves across the field of vision, this suggests a portion of the retina has already detached.