“Seeing stars” or flashes of light, particularly when looking into your armpit, is a common and harmless physiological response. These transient visual sensations can manifest as sparkles, dots, or streaks.
The Science of Seeing Stars
The perception of light without actual light entering the eye is known as phosphenes. This phenomenon occurs because the brain interprets any activation of the retina or optic nerve as visual information. The eye’s photoreceptors, specialized cells in the retina, are designed to detect light but can also be stimulated by non-light sources.
When these photoreceptors or the optic nerve are activated by mechanical pressure, electrical signals, or other stimuli, they send impulses to the brain. The brain processes these signals as if real light were present. This results in the perception of flashes of light, even in darkness or with closed eyes.
Why Your Armpit Triggers It
Looking into your armpit requires a specific head and neck posture, which can inadvertently place temporary pressure on certain areas. This position might compress the eye itself, or more commonly, the optic nerve and surrounding blood vessels. When pressure is exerted on the eyeball, it mechanically stimulates the retinal cells, causing them to fire signals.
Pressure on the optic nerve can also generate these signals. A temporary reduction in blood flow to the eye due to this compression can also contribute to this visual effect. This mechanical stimulation is temporary, ceasing once the pressure is relieved and normal blood flow resumes.
Other Common Triggers for Phosphenes
The armpit scenario is one example of how mechanical stimulation can cause phosphenes; many other common situations also trigger them. Rubbing your eyes, for instance, directly applies pressure to the retina, activating its cells and causing flashes or patterns of light.
Standing up too quickly can also lead to “seeing stars” due to a temporary drop in blood pressure, known as orthostatic hypotension. This momentary reduction in blood flow and oxygen to the brain and eyes can stimulate the retina and optic nerve. Forceful actions like sneezing, coughing, or even a light blow to the head can similarly induce these flashes by creating brief pressure changes within the eye or head.
When to Seek Medical Advice
While the visual disturbances described are harmless, persistent, sudden, or accompanied visual changes can indicate a more serious underlying issue. If you experience new or increased flashes of light, especially if they are sudden, frequent, or accompanied by new floaters (small specks or squiggly lines), a shadow or “curtain” in your vision, or reduced vision, seek prompt medical attention.
These symptoms could be signs of conditions like a retinal detachment or tear, which require urgent treatment to prevent permanent vision loss. Visual disturbances like zigzag lines, shimmering spots, or blind spots that precede or accompany a headache might suggest a migraine with aura. Any sudden or significant change in your vision should be evaluated by an eye care professional.