| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (JR) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Transcript |
Today we're going to be talking about visual hallucinations. A hallucination is seeing something that actually isn't there. So, it's not like an illusion - an illusion is seeing something that is there, but you're misinterpreting what you're looking at. A hallucination occurs without a visual stimulation, and what that means is if you close your eyes, it'll still be there. These hallucinations can result from things inside your eye, which we call entoptic - optic eye, in their eye. The entoptic phenomenon that produced the classic visual hallucinations are things like retinal detachment or posterior vitreal detachment. And because the retina has no thinking power, it's not like cortex, it can only generate a flashing light. It cannot make a geometric figure; it cannot make a person. So, when you have a retinal detachment or a vitreous detachment, you get flashers and floaters. These are entoptic phenomenon. They will still be present even if you close your eye because the retina is being pulled on with traction from the vitreous. So, the flashing light will be in the periphery. And so, any person with flashers and floaters, we need to look in their eye with a dilated fundus examination to make sure it's not a retinal detachment or vitreous detachment. If, however, you have a formed visual hallucination, and by formed we mean it's taking on some form like a geometric form like a circle or a triangle, so if we have a series of little colored circles lasting seconds at a time, that is both eyes at the same time, that is the hallmark for the visual hallucination of occipital seizure. So, when you have an occipital lobe lesion, it forms a geometric figure - usually little colored circles - and we to do an EEG to make sure that that's not occipital seizure. If, however, the formed hallucination is a geometric figure but a jagged line, which we call a fortification scotoma, which looks like the flying over a fort (old forts used to be pointy like this), and especially if it's associated with march and buildup. March - it moves across the visual field. Buildup - it gets bigger over time. So, when a patient who has a fortification scotoma, especially if it's associated with scintillations, which is color or flashing, a bilateral simultaneous positive visual phenomenon lasting minutes, rather than seconds, with a fortification jagged line edge and scintillations, that's way more likely to be migraine. This is the aura of migraine: a jagged line that starts and moves across my peripheral field with both eyes, followed 20 minutes later by the headache. And finally, there's a special type of hallucination called the Charles Bonnet syndrome. The Charles Bonnet syndrome is a formed visual hallucination usually of people or animals. It occurs after vision loss of any type, but the most common is age-related macular degeneration. So, patients who have decreased acuity, say in the 20-40 or worse range, might get a release hallucination. They see people or animals. And you have to ask the patients some seriously weird questions because we're trying to make sure that that's not from psychosis or delirium. In a patient who has the Charles Bonnet syndrome, they have a visual loss problem, usually macular degeneration, but any cause of vision loss can do it. They have full insight into the unreal nature of the phenomenon. They know it's not real. There's also no delusional backstory, so if you ask the person why is that person there, they don't know. And there's no auditory component - it can't talk, and the patient doesn't talk to it. So, they have to know it's not real, they don't talk to it, and there's no reason for it to be there. If you just knew these major categories of visual hallucinations: entoptic, occipital seizure with the little circles, migraine aura with a fortification scintillating scotoma, and the Charles Bonnet phenomenon, you would pretty much know the majority of the visual hallucinations that come to ophthalmology. |
