Phosphenes: Symptoms, Causes and Treatment

Phosphenes are one of the most curious visual phenomena experienced by humans—a flash, swirl, or pattern of light that appears without any corresponding light source entering the eye. Whether it’s seeing stars after rubbing your eyes, or geometric shapes triggered by certain medications or medical procedures, phosphenes can be both fascinating and, at times, concerning. Understanding their symptoms, causes, and available treatments provides not only reassurance but also a window into the intricate workings of our visual system. In this article, we’ll explore what phosphenes are, why they occur, and what can be done if they become bothersome.

Symptoms of Phosphenes

Phosphenes manifest in a variety of ways, making each person’s experience uniquely personal yet sharing some core features. Recognizing these symptoms is the first step to distinguishing phosphenes from other visual disturbances.

Appearance	Color	Duration	Source(s)
Flashes	Blue-violet	Seconds to months	2 6 8
Geometric	Red, green	Brief to persistent	1 5
Spots/lines	White, yellow	Transient	1 2 8
Spirals	Purple	Short-term	5 8

Table 1: Key Symptoms

Visual Appearance

Phosphenes most often appear as brief flashes of light, but they can also present as spots, lines, geometric patterns, or colorful shapes. Some individuals describe swirling, flickering, or even lattice-like grids within their field of vision. In certain neurological conditions, phosphenes can take on more organized geometric forms, such as pyramids, tetrahedrons, or spirals 1 5.

Color and Quality

The color of phosphenes varies widely. Commonly reported shades include blue, violet, white, red, green, yellow, and purple 1 2 5 8. For example, in patients undergoing proton beam therapy for ocular tumors, the majority experienced blue-violet or white phosphenes 8. In cases associated with neurological conditions, red, green, blue, and yellow patterns are frequent 1.

Duration and Frequency

The duration of phosphenes can be fleeting—lasting only a few seconds—or persist for days, weeks, or even months, particularly when linked to underlying pathology 6. Some people experience them only once, while others may have recurrent episodes, especially during ongoing treatments like radiation therapy or when taking certain medications 2 4 7.

Associated Sensations

Phosphenes may be accompanied by other sensations. For instance, during radiation therapy, some individuals simultaneously experience unusual smells (phantosmias) along with their visual disturbances 2. In rare cases, sound can also trigger phosphenes, especially in those with existing visual impairment 6.

Causes of Phosphenes

Understanding what triggers phosphenes is critical for both clinicians and individuals experiencing these unusual visual events. Causes can range from entirely benign to indicative of underlying neurological or retinal conditions.

Trigger	Mechanism	Typical Context	Source(s)
Mechanical	Retinal stimulation	Rubbing eyes, pressure	4
Electrical	Retinal/cortical	tES, radiation therapy	2 3 8
Medication	HCN/Ih channel block	Ivabradine, others	4 7
Pathological	Lesion/functional	Stroke, nerve damage	1 6

Table 2: Key Causes

Mechanical Stimulation

The most familiar cause of phosphenes is mechanical stimulation of the eye—rubbing your closed eyes, applying gentle pressure, or experiencing a sudden jolt. This pressure directly stimulates the retina, causing the perception of light even in darkness 4.

Electrical and Radiation-Induced Phosphenes

Transcranial electrical stimulation (tES), such as that used in research or therapy, can produce phosphenes due to electrical currents reaching the retina or visual cortex 3. Notably, radiation therapy, especially in the head, neck, or ocular region, frequently triggers phosphenes. Here, patients often see flashes or colored lights—typically blue, violet, or white—due to the stimulation of retinal cells or visual pathways by the radiation itself 2 8. The activation of S-cones (short-wavelength sensitive cones) and retinal ganglion cells is thought to underlie these effects 8.

Medication Side Effects

Certain medications can induce phosphenes as a side effect. A notable example is ivabradine, a heart-rate-lowering drug. Ivabradine blocks hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which are present both in the heart and the retina. Blocking these channels in retinal neurons alters the balance between the On and Off visual pathways, making spontaneous light sensations more likely 4 7.

Neurological and Pathological Causes

Phosphenes can signal underlying neurological or retinal pathology:

• Stroke or Lesions: Small, localized brain lesions, especially in the occipital lobes, may disrupt normal visual processing and lead to persistent, colored geometric phosphenes 1.
• Visual Pathway Disorders: Damage to the optic nerve (e.g., neuritis, compression) or retinal disease can result in phosphenes, sometimes lasting for extended periods 6.
• Cortical Hyperexcitability: In some cases, such as migraine or epilepsy, abnormal cortical activity can generate complex geometric visual patterns 1 5.

Multisensory and Unusual Triggers

Sound-induced phosphenes are rare but have been documented in individuals with visual impairment. Cross-activation between auditory and visual brain areas—especially when the brain’s normal input is disrupted—can lead to these unusual experiences 6.

Treatment of Phosphenes

While phosphenes are usually benign and self-limiting, persistent or distressing cases may require medical evaluation and management. The approach to treatment depends on the underlying cause and the impact on daily life.

Approach	Target	Effectiveness	Source(s)
Reassurance	Benign cases	High	4 8
Medication	Underlying condition	Variable	4 7
Adjust Therapy	Radiation/Drugs	High/Variable	2 8
Neurological Care	Brain/nerve lesions	Variable	1 6

Table 3: Treatment Strategies

Reassurance and Observation

For most people, phosphenes are harmless and transient. Simple reassurance and observation are sufficient, especially when the cause is mechanical (e.g., rubbing eyes) or related to brief stimulation during medical procedures 4 8. Educating patients about the benign nature of most phosphenes can alleviate anxiety.

Medication Management

When phosphenes are linked to medication—such as ivabradine or other HCN channel blockers—adjusting the medication dose or switching to an alternative may reduce or eliminate symptoms 4 7. In some cases, the phosphenes resolve as the body adapts to the medication or after the drug is discontinued.

Addressing Underlying Medical Conditions

If phosphenes are a symptom of an underlying neurological or retinal disorder, targeted treatment of the primary condition is crucial. For example:

• Stroke or Brain Lesions: Management of the cerebrovascular event and neurorehabilitation may lead to resolution of phosphenes, as observed in patients whose visual deficits improved over time 1.
• Optic Nerve or Retinal Disease: Treating the underlying cause (e.g., inflammation, compression) may reduce or stop phosphenes 6.

Modifying Radiation or Electrical Therapies

In patients experiencing phosphenes during radiation therapy or transcranial electrical stimulation, modifying treatment parameters—such as adjusting the radiation field or current amplitude—may help. However, these sensations are often temporary and do not require intervention unless they become bothersome 2 3 8.

Supportive Care and Monitoring

Persistent or distressing phosphenes warrant further evaluation to exclude serious underlying disease. In select cases, referral to a neurologist or ophthalmologist, visual field testing, and imaging studies may be indicated 1 6.

Conclusion

Phosphenes are a vivid reminder of the complexity of the human visual system and its interplay with the brain and environment. While most phosphenes are harmless, their occurrence can sometimes signal underlying medical issues or be a side effect of treatments. Understanding their symptoms, causes, and management options helps patients and clinicians alike to navigate these curious sensations with confidence.

Key points covered in this article:

• Phosphenes are visual sensations, such as flashes or geometric patterns, that occur without external light.
• Symptoms include a wide range of visual phenomena across various colors and durations, sometimes accompanied by other sensory experiences.
• Causes span mechanical stimulation, electrical and radiation therapies, medications, and neurological or retinal disorders.
• Treatment focuses on reassurance for benign cases, medication adjustment or therapy modification for induced cases, and targeted care for underlying medical conditions.
• Evaluation is important for persistent or distressing phosphenes to rule out serious disease.

By demystifying phosphenes, we empower individuals to better understand their visual experiences and seek help when necessary, ensuring eye and brain health are maintained.