Seeing swirling colors, flashes of light, or intricate patterns after pressing on a closed eyelid is a common phenomenon known as a phosphene. A phosphene is the perception of light that occurs without any actual light entering the eye. The word originates from the Greek words for “light” and “to show,” describing a self-generated light sensation. These visual displays demonstrate that the visual system can be activated by stimuli other than photons.
How Pressure Creates Visual Signals
The momentary light show is a response generated at the back of the eye, specifically the retina. The retina contains specialized nerve cells, including photoreceptors, which are typically activated by light energy. When the eye is rubbed, the physical pressure deforms the eyeball, causing mechanical stimulation of these light-sensitive cells.
The photoreceptors respond to this mechanical force by firing electrical impulses, similar to being struck by light. These signals travel along the optic nerve to the brain’s visual processing centers. Since the brain interprets signals from the retina as vision, it processes the mechanically induced impulses as patterns of light and color.
Why the Patterns Are Geometric
The resulting phosphenes often appear as organized, intricate shapes like grids, checkerboards, radiating stars, or swirling tunnels rather than random noise. This organization is thought to originate not in the retina, but higher up in the visual pathway, likely the visual cortex (V1). The visual cortex processes raw visual information and is highly structured.
The visual system contains an inherent structural map, with neurons arranged in columns that respond specifically to features like edges and lines. When the retina is stimulated non-specifically by pressure, it sends a disorganized barrage of signals to the cortex. The brain attempts to interpret this chaotic input by mapping it onto its internal, ordered network. This interpretation causes the brain to perceive the input based on its own geometric organization, resulting in the structured, periodic patterns the observer sees.
Risks Associated with Eye Rubbing
Although the phosphene experience is a fascinating demonstration of neurobiology, repeated or vigorous eye rubbing carries several health risks for the eye’s delicate structures. One immediate concern is the potential for scratching the cornea, the transparent outer layer of the eye. Rubbing can also temporarily spike the intraocular pressure (IOP), the fluid pressure inside the eye.
Sustained increases in intraocular pressure are a concern because they can stress the optic nerve fibers at the back of the eye, similar to the damage seen in conditions like glaucoma. Furthermore, chronic, forceful eye rubbing is strongly associated with the development or progression of keratoconus.
Keratoconus is a progressive condition where the cornea thins and bulges outward into a cone shape, causing distorted vision. The mechanical stress of rubbing is believed to weaken the collagen fibers within the cornea, accelerating this progressive thinning.