Welcome to a new feature in which we explore the various fascinating conditions that can cause various fascinating symptoms, kicking off today with visual hallucinations. Since the goal is curiosity, rather the actual medical utility, these won’t be exhaustive lists of causes. I will include only those conditions that I deem worthy of my time and yours. Additionally, I can’t promise that this feature will be delivered with monthly regularity. I was imagining a timeframe more along the lines of “whenever I feel like it”. That said, I would like to offer the last and most important disclaimer: I am not a doctor and indifferential is not a word. The rest of the information contained here is true to the best of my knowledge. Feel free to use it at dinner parties and when competing against computers on game shows.
A visual hallucination can be summarized as the perception of an external image in the absence of any existing object. This is different from an illusion, in which one perceives a distorted view of one’s surroundings. Visual hallucinations can be simple (shapes and colors) or complex (vivid landscape or figures). Both categories vary not only in their causes, but also in their appearance, a variation that can at times provide insight into the source of the problem.
While many associate visual hallucinations with mental illness, this symptom is not particularly common in schizophrenia or other psychotic disorders. The bulk of hallucinations occurring in schizophrenia are auditory. When visual hallucinations do occur, they are generally complex and may involve humans, animals, and religious figures. The specific content of these visuals may have symbolic value to the person seeing them and are often threatening, or even hostile toward the viewer.
Tell-tale signs: Schizophrenia usually manifests with a host of other psychological symptoms – auditory hallucinations (often disparaging in content), delusions, and disorganized thought – that easily separate it from most of the other conditions we will be looking at.
As you probably know, a migraine is a really, really, really bad headache. They can last hours to days and may be accompanied by light sensitivity, nausea and vomiting. If this weren’t bad enough, about a third of migraines commence with a phenomenon known as an “aura” that includes a hallmark visual hallucination. This starts with a simple, usually colorless, flickering and then proceeds to a zig-zag line that spreads from the center of the visual field outward, often leaving a vision-obscuring blotch (called a scotoma) in its wake. The good news is that this phase will be over in an hour or less. The bad news is that if will be followed by an excruciating headache.
Tell-tale signs: The horrible pain associated with a migraine is a pretty good give away as to the cause of this hallucination. Unless, of course, you suffer from…
…Occipital Lobe Seizures
The occipital lobe is the part of the brain where visual processing occurs, so it’s not surprising the electrical abnormalities in this region can cause visual hallucinations. Unlike the classic tonic-clonic (“grand mal”) seizure, which affects the entire brain and features loss of consciousness and convulsions, occipital lobe seizures are pretty subtle.* An observer of such an event may see nothing more than rapid fluttering of the eyelids. But to the person having the seizure, things look quite different. As with migraines, visual hallucinations attributed to this condition are simple and have a consistent design. They are brightly colored and dominated by many circular or spherical shapes. However, the lightshow is much shorter than that of the migraine aura, lasting no more than a few minutes. Despite striking differences in visual content and duration, occipital seizures are frequently mistaken for migraine auras. This is because up to half of such seizures are followed by headaches.
Tell-tale signs: If you’re lucky enough to have health insurance, epilepsy can often be confirmed with an expensive EEG. Just be sure to bring a hat, because they stick those recording electrodes right in your hair with some nasty gel that won’t come out until it’s shampooed.
Charles Bonnet Syndrome
And now we return to the realm of complex visual hallucinations. Charles Bonnet syndrome (CBS) is a condition in which subjects with impaired vision start seeing things. The hallucinations are vivid and elaborate and can involve figures and animals.† They tend to begin in the evening and can last for hours. CBS is most common in older people (possibly because their rate of failing eyesight is higher than the general population) and is unfortunately sometimes mistaken for age-related mental deterioration. However, unlike the complex hallucinations experienced by psychotic patients, these are strikingly lacking in symbolism and contain no special meaning to the people experiencing them.
Tell-tale signs: Oldness and/or near-blindness. Additionally, patients with this condition are perfectly aware that what they are seeing is not real and, aside from nagging doubts about the state of their sanity, generally do not find the hallucinations especially bothersome.
Didn’t I already cover this back in October? It’s true though, visual hallucinations can occur during transitions between waking and sleeping states of consciousness.
Tell-tale signs: It’s dark and/or you’re in bed.
With all due respect to the alleged horrors of opiate withdrawal, I must say that delirium tremens (aka the DTs) sounds utterly miserable. It occurs following the abrupt cessation of ethanol consumption after a long period of heavy drinking. Symptoms begin with the characteristic tremor and progress to include fever, confusion, agitation and, of course, visual hallucinations. In addition to being unpleasant, this particularly ugly variation of chemical withdrawal can be fatal. The hallucinations vary in duration (brief to almost continuous) and often involve animals. And these aren’t always cute cuddly animals, visions of snakes and insects have been reported by some patients. The severity of delirium tremens can be reduced with benzodiazepines (Klonopin and company), which ironically can also be habit-forming and feature similar withdrawal symptoms if discontinued too suddenly.
Tell-tale signs: Um, history of heavy drinking, shaking, etc. Really, this one sounds kind of hard to miss.
* Seizures that begin localized in one portion of the brain can spread to the rest of the organ, so those prone to occipital lobe seizures may also suffer from grand mal seizures.
† One patient reported seeing Highland cattle grazing in his living room.
Who told you this?
Teeple, R.C. et al. 2009. “Visual Hallucination: Differential Diagnosis and Treatment.” Prim Care Companion J Clin Psychiatry 11: 26-32.
Manford, M. and Andermann, F. 1998. “Complex visual hallucinations, Clinical and neurobiological insights.” Brain 121: 1819-1840.
Panayiotopoulos, C. P. 1994. “Elementary visual hallucinations in migraine and epilepsy.” J Neurol Neurosurg Psychiatry 57: 1371-1374.
Jacob, A. et al. 2004. “Charles Bonnet syndrome – elderly people and visual hallucinations.” British Journal of Medicine 328: 1552-1554.