The investigators no longer want to do the project

NEVICOG is a single-center study evaluating neurovisual and radiological specificities in patients with visual snow syndrome (VSS) compared to a control population.

Visual snow syndrome (SNV) is characterized by a continuous grainy or pixelated visual sensation additional to the perceived image. Patients often report a feeling similar to seeing noise from cathode-ray televisions.

The prevalence is not well known but about 2% of the population could be reached. Although benign and stable, this pathology is often troublesome in everyday life.

Its precise etiology remains unknown to this day. Ophthalmologic explorations do not reveal any significant abnormalities. Neurologically, "standard" examinations appear normal. Only the examinations carried out in the context of research have been able to highlight anomalies such as an imbalance between visual cortical inhibition and excitation as well as a high spontaneous neural triggering and hypermetabolism of the associative visual cortex (functional MRI, PET- MRI). In addition, the Visual Evoked Potentials show a lack of habituation, testifying to cortical hyperexcitability.

To our knowledge, no specific neurovisual study focusing on the functions involved in the processing of visual information has been carried out to date. We propose the realization of a complete evaluation made up of existing tasks as well as the adaptation of some of them specific to SNV.

The posterior abnormalities currently highlighted by imaging have been carried out in examinations not available on a daily basis. A non-invasive brain MRI study will be carried out in our patients using more recent techniques (MRI with arterial spin labelling or ASL for Arterial Spin Labelling, and diffusion tensor imaging or DTI for Diffusion Tensor Imaging) in order to search for possible posterior lesions and clinical radiological correlations.

Thus, this study aims to carry out a more in-depth neurovisual exploration of this syndrome, in order to allow a better understanding of this frequent and disabling disorder on a daily basis.

Inclusion Criteria:

Case group:

• Patient aged up to 55
• Diagnosis of visual snow syndrome according to the international criteria
• Visual snow symptoms still present
• Express consent to participate in the study

Control group:

• Person aged up to 60
• Matched to an SNV patient on age (+/- 5 years) and sex
• Express consent to participate in the study

Exclusion Criteria:

Case group:

• Patient with an absolute or relative contraindication to MRI (claustrophobia, incompatible implantable device, etc.)
• Patient benefiting from a legal protection measure
• Pregnant or breastfeeding woman
• Non-French speaking patient
• Added psychiatric or neurodegenerative pathology unrelated to visual snow likely to induce neurocognitive and neurovisual disorders in the short or long term
• Ophthalmologic comorbidity that may interfere with the interpretation of examinations

Control group:

• Patient with an absolute or relative contraindication to MRI (claustrophobia, incompatible implantable device, etc.)
• Person benefiting from a legal protection measure
• Pregnant or breastfeeding woman
• Non-French speaking person
• Psychiatric or neurodegenerative pathology likely to induce neurocognitive and neurovisual disorders in the short or long term
• Ophthalmologic comorbidity that may interfere with the interpretation of examinations

Patients diagnosed with of visual snow syndrome according to international criteria compared to control patients without any visual snow syndrome