Visual hallucinations: examples, causes

Filaments, dots, flying fly print… This phenomenon results, most of the time, from the aging of the vitreous, a translucent gel that fills the eyeball. « This gel is very homogeneous in a young person, it is less so as you get older », explains Dr. Olivier Offret, retinologist and member of the French Society of Ophthalmology.

With age, the vitreous tends to dehydrate and shrink. Small fragments of its cortex break off and then begin to float haphazardly. Most of the time, these floaters do not interfere with vision, although they can be annoying.

These filaments and dots appear more easily in certain situations: “We mostly see them when the light is strong, when working in front of a paper or a white wall, or even facing a computer screen », observes Dr. Offret.

If these small spots appeared gradually and they remain mobile, there is no need to worry, even if it is important to talk to your ophthalmologist. In consultation, he will verify that the problem is simply related to aging. In this case, the only cure is patience. After a while, the brain will get used to these visual oddities and the patient will no longer pay attention to them. “The brain is able to forget these abnormalities, but it can take several years,” recognizes the retinologist.

In the rare cases where « flying flies » actually interfere with vision, especially driving a car, a laser treatment can be considered. “It’s a matter of breaking up floaters that are too big. It is also possible to practice a vitrectomy, that is to say the ablation of the vitreous. But this type of surgery can have consequences, with a risk of cataracts or retinal detachment. We must carefully weigh the risk-benefit balance before making a decision. insists the ophthalmologist.

On the other hand, it is necessary to react as quickly as possible if these floaters are accompanied by bright flashes. It is an emergency because it can be a tear, or even the beginning of retinal detachment. Indeed, it happens that by retracting, the vitreous exerts too strong a traction at the level of the retina. Instead of coming off, he tears it.

In consultation, the ophthalmologist will check the fundus of the eye.  » In case of retinal teara laser treatment will prevent the formation of a detachment by creating a scar around the lesion”, explains Dr. Offret.

Another scenario: a black spot, fixed, hindering central vision. You must consult an ophthalmologist very quickly, especially if this spot occurs suddenly, in a person over 60 years of age. “Very often, the problem is related to a retinal hemorrhage coming from an abnormal choroidal blood vessel located under the macula (the central zone of the retina, editor’s note). If it is accompanied by a deformation of the vision, it may be AMD (age-related macular degeneration). You need to start treatment as soon as possible to give yourself the best chance of recovering and preserving your vision.” explains Dr. Offret.

Some people complain of real hallucinations: they see things that aren’t there, like geometric shapes, characters or animals. In this case, it is likely that the problem comes from the brain and not from the eye. Indeed, a neurological (ophthalmic migraine), neurodegenerative (Parkinson, Lewy body disease, etc.) or psychiatric (schizophrenia, etc.) disease may be involved. Taking drugs can also disrupt brain function and generate visual hallucinations.

Three of the most common examples:

This type of migraine starts with an « aura », that is to say neurological symptoms, mostly visual. They can be very varied. Sometimes the patient has the impression of looking at a kaleidoscope. He can also see myriads of luminous pointsfrom stripes, from geometric patterns or some colored spots. More rarely, the person sees blurry and their visual field is temporarily reduced. “These symptoms usually last less than thirty minutes. They are followed by typical migraine symptoms like headache and nausea. Moreover, the person can no longer bear the light,” observes Dr. Offret.

This syndrome manifests itself in certain pathologies such as atrophic macular degeneration advanced, a disease that mainly affects the elderly. In these patients suffering from a serious sensory deficit, the brain receives anarchic information. It could then generate visual hallucinations. « In this case, the treatment of hallucinations involves the prescription of neuroleptic drugs to reduce neuronal excitation », explains Dr. Offret.

Certain neurodegenerative diseases, such as dementia with Lewy bodies, can also cause visual hallucinations. 80% of patients experience it, especially in the early stages of the disease, according to the France Alzheimer and related diseases association (source 1). Again, it is the malfunctions of the brain that cause the hallucinations and not a vision disorder.