Seeing Bugs That Aren't There: Causes of Visual Hallucinations

Seeing insects or bugs that aren't present (visual hallucinations) can arise from ocular, neurological, psychiatric, or systemic causes. Accurate diagnosis requires distinguishing the type of phenomenon.

1. Entoptic Phenomena (Eye-Based, Not Hallucinations)

• Floaters (myodesopsias): Vitreous opacities casting shadows on retina. Dark spots, threads, "cobwebs" moving with eye movement. Benign usually; sudden increase + flashes = retinal tear evaluation.
• Blue field entoptic phenomenon: White blood cells moving in retinal capillaries against blue sky — "flying corpuscles."
• Phosphenes: Mechanical retinal stimulation (eye rubbing, trauma) → flashes.

2. True Visual Hallucinations (Formed Images Without External Stimulus)

Ocular / Visual Pathway

• Charles Bonnet Syndrome: Complex, vivid hallucinations (people, animals, geometric patterns) in visually impaired elders with intact cognition. Due to cortical release from sensory deprivation. Not psychotic.
• Migraine aura: Scintillating scotoma, fortification spectra, zigzags — usually precede headache.
• Occipital lobe lesion: Tumor, stroke, AVM → formed hallucinations in contralateral field.

Neurological / Systemic

• Delirium: Acute encephalopathy (infection, metabolic, drugs, withdrawal) — fluctuating attention, visual hallucinations common.
• Lewy body dementia / Parkinson's disease dementia: Early, detailed visual hallucinations (people, animals).
• Seizures (occipital / temporal): Brief, stereotyped visual phenomena.
• Narcolepsy: Hypnagogic/hypnopompic hallucinations at sleep transitions.

Psychiatric

• Schizophrenia / schizoaffective: Auditory > visual, but visual occurs.
• Severe mood disorders with psychotic features.

Substance-Related

• Hallucinogens (LSD, psilocybin, mescaline)
• Stimulant intoxication (cocaine, methamphetamine) — "formication" (bugs crawling on skin)
• Alcohol/sedative withdrawal (delirium tremens)
• Anticholinergic toxicity (diphenhydramine, scopolamine, TCAs)

3. Illusions / Misinterpretations

• Pareidolia: seeing patterns in randomness (faces in clouds, bugs in texture)
• Peripheral vision misidentification (low light, anxiety)

When to Seek Evaluation

• New-onset hallucinations (especially if formed, complex)
• Associated confusion, memory loss, gait change, headache
• Known visual impairment + new hallucinations (Charles Bonnet — reassurance often sufficient)
• Medication review (anticholinergics, dopaminergics, opioids, benzos)

Start with primary care or ophthalmology; may need neurology, psychiatry, or neuro-ophthalmology referral.