Seeing specks, spots, or flashes of light in a dark environment or with the eyes closed is a common phenomenon. These visual occurrences are generated internally by the eye and brain. These perceptions are harmless and represent the normal functioning of the visual system when it is deprived of outside stimuli. The dots and flashes are divided into two categories based on their origin: self-generated light signals and internal shadows.
Understanding Phosphenes
The light you perceive in complete darkness, often as shimmering patterns, swirls, or flashes, is known as a phosphene. Phosphenes are perceptions of light produced by the visual system without actual photons entering the eye. The visual system, which includes the retina and the optic nerve, is always active, and the brain interprets any stimulation it receives as light.
Phosphenes can be triggered by various forms of mechanical stimulation. A common example is the “pressure phosphene,” which occurs when you gently rub or press on your closed eyelids. This pressure physically stimulates the light-sensitive cells of the retina, causing them to fire signals that the brain recognizes as a temporary flash or colored pattern. The location of the perceived light often appears opposite to where the pressure is applied.
Even without external pressure, phosphenes can arise from spontaneous nerve activity. When the photoreceptor cells in the retina are not receiving environmental light, they can still fire random signals. The brain’s attempt to process this lack of visual input, especially in total darkness, results in the perception of moving shapes or faint light known as “prisoner’s cinema”.
Rapid eye movement, such as when waking up or quickly shifting gaze, can also induce phosphenes. This rapid motion temporarily stretches or compresses the optic nerve and the retina, momentarily stimulating the neural pathways. The resulting perception is often a brief, bright spot or ring, especially noticeable against a dark background.
How Floaters Appear
Floaters are distinct from phosphenes because they are shadows cast upon the retina by microscopic debris inside the eye. These specks are correctly termed muscae volitantes, or “flying flies,” and they are small condensations of protein or collagen fibers suspended in the vitreous humor, the clear, gel-like substance filling the eye.
As light passes through the eye, these deposits intercept the light and cast a shadow onto the retina, which the brain perceives as a floating shape. Floaters commonly appear as threads, cobwebs, dots, or squiggly lines that drift across the field of vision when the eye moves. Because they are suspended in the gel, they lag slightly behind the eye’s movement.
While floaters are most noticeable when looking at a bright, uniform background, they also become apparent in low-light conditions. In the dark, subtle eye movements cause the shadows to shift and become visible against the uniform visual field. This perception is an entoptic phenomenon, meaning the source of the visual experience originates within the eye structure itself.
Recognizing Serious Symptoms
While most dots and flashes are harmless phosphenes or floaters, a sudden change in their appearance can signal a more serious underlying condition. A sudden increase in the number of floaters, especially if accompanied by flashes of light, is a symptom known as photopsia and may indicate a problem with the retina.
The flashes of light, often described as lightning streaks in the peripheral vision, occur when the vitreous gel pulls or tugs on the retina. This pulling sensation mechanically stimulates the retinal nerve cells, and the brain interprets this stimulation as light. This scenario is characteristic of a Posterior Vitreous Detachment (PVD), a harmless, age-related condition where the vitreous naturally shrinks and separates from the retina.
However, PVD symptoms can mimic a more concerning issue: a retinal tear or detachment. If the vitreous pulls too hard, it can create a tear. Fluid can then seep through this tear, causing the retina to peel away from the supportive tissue beneath it. Retinal detachment is a medical emergency that can lead to permanent vision loss if not treated promptly.
Other warning signs include the sudden appearance of a dark curtain or shadow moving across the field of vision or a noticeable loss of peripheral sight. If you experience a sudden onset of numerous new floaters, persistent flashes of light, or any shadow obscuring your vision, consult an eye care professional immediately to rule out a sight-threatening condition.