Open-eye hallucinations occur when your brain generates vivid visual experiences without any real external stimulus present. Unlike the brief images that can flash during the transition to sleep, these happen while you’re fully awake and your eyes are open. The causes range widely, from vision loss and neurological disease to substance use, sleep deprivation, and psychiatric conditions, each involving a distinct mechanism in the brain.
How the Brain Creates What Isn’t There
All visual hallucinations share a common thread: abnormal activation of the brain’s visual processing areas. Neuroimaging studies consistently show heightened activity in the visual cortex during hallucinatory episodes. Under normal circumstances, the visual cortex processes signals coming in from the eyes. When those signals are disrupted, reduced, or overridden by internal brain activity, the cortex can fire on its own and produce images that feel completely real.
What separates a true hallucination from a simple visual mistake is important. An illusion is a distortion of something that actually exists, like mistaking a shadow for a person. A hallucination has no external trigger at all. It’s generated entirely within the brain, and the person experiencing it typically perceives it as real, solid, and located in the physical world around them. This quality of seeming genuinely “out there” is what distinguishes hallucinations from other experiences like daydreaming or mental imagery, where you recognize the images are coming from your own mind.
Vision Loss and Charles Bonnet Syndrome
One of the most common and least recognized causes of open-eye hallucinations is simply losing your eyesight. Charles Bonnet Syndrome (CBS) occurs when reduced input from the eyes causes the visual cortex to become hyperexcitable and start generating its own images. The mechanism is similar to phantom limb pain after an amputation: the brain keeps producing sensations from a source that’s no longer sending signals.
People with CBS see formed, vivid images like faces, animals, geometric patterns, or miniature figures. These aren’t vague impressions. They can be detailed and colorful. The syndrome predominantly affects adults over 65, reflecting the high prevalence of age-related eye diseases like macular degeneration, glaucoma, and diabetic retinopathy. The typical patient is between 70 and 85 years old, and there’s a slight female predominance, likely because women live longer and develop macular degeneration at higher rates.
Crucially, people with CBS are mentally healthy. They usually recognize that what they’re seeing isn’t real, even if the images are startling. The hallucinations are a product of sensory deprivation, not mental illness, and many people never mention them to a doctor out of fear they’ll be thought to have dementia or psychosis.
Neurodegenerative Disease
Visual hallucinations are a hallmark of certain brain diseases, particularly Parkinson’s disease and Lewy body dementia. In Parkinson’s, the lifetime prevalence of visual hallucinations approaches 75%, making them one of the most common non-motor symptoms of the disease. These hallucinations often begin as mild misperceptions (seeing movement in the corner of your eye, for instance) and can progress to fully formed images of people or animals.
The underlying cause involves disruptions to the brain’s dopamine and acetylcholine systems, both of which play roles in regulating perception and attention. Medications used to treat Parkinson’s, particularly dopamine-boosting drugs, can also contribute to or worsen hallucinations. In Lewy body dementia, recurrent, well-formed visual hallucinations are so characteristic that they’re one of the core diagnostic features. Patients may describe detailed scenes involving strangers in their home or animals that aren’t there.
Psychiatric Conditions
While auditory hallucinations (hearing voices) get the most attention in conditions like schizophrenia, visual hallucinations are more common than many people realize. In a cross-cultural study comparing patients in the US and India, 57% of American patients with schizophrenia reported visual hallucinations, and 37% of Indian patients did. These typically occur alongside auditory hallucinations rather than in isolation.
Visual hallucinations in schizophrenia can include faces, figures, or entire scenes and tend to carry emotional significance, often reflecting the person’s fears or delusions. Unlike CBS, there’s usually no preserved insight. The person experiencing the hallucination believes it’s real.
Psychoactive Substances and Serotonin
Classic hallucinogens like psilocybin (the active compound in psychedelic mushrooms) and LSD produce open-eye visual hallucinations primarily by activating a specific type of serotonin receptor in the brain. Research from the University of Zurich demonstrated this by giving participants psilocybin and then blocking those receptors with another drug, which completely eliminated the visual effects. The hallucinations appear to result from disrupted processing of incoming visual signals, causing the brain to overlay patterns, colors, and distortions onto what you’re actually seeing.
Other substances produce hallucinations through different pathways. Anticholinergic drugs, which block acetylcholine signaling, are known to cause vivid and often frightening visual hallucinations. This category includes some older antihistamines (like diphenhydramine in high doses), certain bladder medications, and plants like jimsonweed. Stimulants like methamphetamine and cocaine can also trigger visual hallucinations, particularly during binges or with chronic use, through excess dopamine activity.
Alcohol and Sedative Withdrawal
When someone who has been drinking heavily for a prolonged period suddenly stops, the brain’s chemical balance is thrown into an excitatory state. Chronic alcohol use forces the brain to compensate for alcohol’s sedating effects by ramping up excitatory signaling and dialing down its own calming signals. Remove the alcohol, and you’re left with a brain that’s dramatically overstimulated.
Visual hallucinations during alcohol withdrawal typically appear within the first 48 hours after the last drink. This stage, called alcohol hallucinosis, affects roughly 2% of people going through withdrawal and can include seeing insects, animals, or threatening figures. These hallucinations usually resolve within 72 hours. In more severe cases, withdrawal can progress to delirium, which involves not just hallucinations but also fever, rapid heart rate, confusion, and agitation. Risk factors for severe withdrawal include being over 65, having had withdrawal seizures before, and simultaneous dependence on benzodiazepines.
Sleep Deprivation
Going without sleep is one of the most reliable ways to induce hallucinations in otherwise healthy people. The progression follows a surprisingly predictable timeline. Within the first 24 to 48 hours without sleep, visual distortions begin: objects appear to change shape, size, or depth. By 30 to 48 hours, simple hallucinations emerge, like flashes of light or brief images. After 48 hours, the effects become more dramatic, with 87.5% of sleep deprivation studies reporting perceptual distortions and hallucinations at that point. By 72 hours, full delusions can develop, and the overall picture starts to resemble acute psychosis.
These aren’t the same as hypnagogic hallucinations, which are the brief, dreamlike images many people experience as they’re falling asleep, or hypnopompic hallucinations, which occur while waking up. Those are normal and involve dream imagery intruding into a semi-conscious state. Sleep deprivation hallucinations happen during full wakefulness and involve different types of imagery, more complex scenes and objects rather than the light flashes and floating faces typical of the sleep-wake transition.
Migraine With Aura
Migraine aura produces visual disturbances that can sometimes be confused with hallucinations, but they’re distinct. Aura typically involves zigzag lines, blind spots, flickering lights, or shimmering patches that expand across your visual field. These usually last 15 to 35 minutes and are caused by a wave of electrical activity spreading across the visual cortex, not by the kind of spontaneous firing that produces true hallucinations.
That said, migraine can in rare cases trigger genuine complex visual hallucinations. Case reports describe fully formed, colorful images in motion: people, animals, even words written on walls. These episodes last much longer than typical aura, sometimes days to weeks, and are thought to involve a different mechanism. Most visual disturbances associated with migraine, though, fall into the aura category and are brief, geometric, and easily distinguished from the formed images of a true hallucination.
Medications as a Hidden Cause
Several classes of commonly prescribed medications can trigger visual hallucinations, particularly in older adults. The drugs most frequently implicated share a few properties: they cross into the brain easily, and they have anticholinergic or dopaminergic activity. The highest-risk categories include sedatives, opioid painkillers, certain antiseizure medications, first-generation antihistamines (such as hydroxyzine and promethazine), tricyclic antidepressants, and bladder control medications like oxybutynin and tolterodine.
The risk increases when multiple medications with anticholinergic effects are taken together, a situation common in older adults managing several conditions at once. Kidney problems can amplify the risk further by allowing drugs to reach higher concentrations in the brain. If hallucinations appear shortly after starting a new medication or adjusting a dose, the drug is a likely contributor.