Cognitive impairment and dementia are primarily due to a combination of vascular brain injury and neurodegenerative lesions. The vascular component is now recognized as a major contributor to the pathophysiology of dementia, with small vessel disease (SVD) being its most frequent substrate. This study aims to collect retinal microvascular markers as well as various parameters related to blood pressure and arterial stiffness, in a young adult population. The main objective is to explore the association between these parameters and structural changes on brain MRI. Results will allow to determine the most relevant biomarkers associated with very early brain imaging markers of SVD.

Small Vessel Disease is most often covert i.e detectable only on brain images without being associated with a clinical stroke. Covert SVD (cSVD) is highly prevalent in older persons from the general population and is a powerful predictor of future cognitive decline and dementia risk. Better detection of covert cSVD, particularly at the earliest stages, would have a major impact on preventing disability and costs related to stroke, cognitive impairment and dementia. Studying the association of retinal and vascular biomarkers with MRI markers of brain structure will enable to facilitate the detection of patients at high risk of developing cSVD and its complications. This study aims to collect ophthalmological (retinal image acquisition - Part 1 of the study) and blood pressure / arterial stiffness (vascular assessment - Part 2 of the study) markers from 400 young adults from the Bordeaux bio-Share study. In Part 1, microvascular retinal biomarkers will be revealed by two complementary advanced technologies: the Swept-source optical coherence tomography angiography (SS-OCT-A) and the Adaptative Optics (AO). In Part 2, participants will benefit from an in-depth vascular assessment.

Inclusion Criteria: Young adults from the i-Share cohort will be included in the study:

• having signed the informed consent form of the MRi-Share sub-study,
• having signed the informed consent form for the bio-Share sub-study,
• for whom brain MRI images and for whom the results of the genome-wide genetic association study (GWAS) are of good quality
• having signed freely, an informed and written consent for this study (at the latest on the day of inclusion and before any examination required by the research),
• being affiliated with social security.

Exclusion Criteria: Will not be included in the study:

• participants with severe myopia greater than -6 dioptres
• participants with known allergy to Tropicamide (Mydriaticum®)