Reversible cerebral vasoconstriction syndrome (RCVS) is a clinico radiological entity characterized by severe headaches (associated or not with neurological complications) during one to 3 weeks, associated with a characteristic 'string and beads' appearance on cerebral arteries, which resolves spontaneously in 3 months. The pathway is unknown. At early stage of the disease (at the first medical consultation) cerebral arterial abnormalities which are necessary for diagnosis are identified in only 20% of patients (brain magnetic resonance imagery (MRI) ,CT scan angiography), appearing with a delay on 2th or 3rd week after the first severe headache..

Retinal artery network is considered to be a window on brain microvasculature by sharing the same embryologic origin and physiopathology. A retinal arteriolar examination at early stage of RCVS could provide non invasively early clue to confirm diagnosis by identifying anatomical change and /or functional abnormalities at the microvascular level, whereas large cerebral artery abnormalities are still normal.

Reversible cerebral vasoconstriction syndrome (RCVS) is a clinico radiological entity characterized by severe headaches (associated or not with neurological complications) during one to 3 weeks, associated with a characteristic 'string and beads' appearance on cerebral arteries, which resolves spontaneously in 3 months.

The pathway is unknown. One strong hypothesis is that RCVS is a vasospasm and-vasodilatation disorder starting from small distal cerebral arteries progressing toward to medium sized and large sized cerebral arteries, and disappearing in 3 months.

At early stage of the disease (generally at the first medical consultation round 7 days after the first headache), arterial caliber anomalies cannot be identified on usual investigation (brain MRI, angioscan) in most of the case (80%). They are appearing secondary on repeated angiogram around the 2nd week or 3rd week, permitting to confirm the diagnosis, but with delay. Currently, small cerebral vessel arteries can't be studied directly . Retinal artery network is easy to study. It is considered to be a window on brain microvasculature by sharing the same embryologic origin and physiopathology. The investigators thus hypothesized that retinal arteriolar examination a early stage of RCVS could provide non invasively early clue to confirm diagnosis by identifying anatomical change and /or functional abnormalities at the microvascular level, whereas large cerebral artery abnormalities are still normal.

Hypothesis Arteriolar caliber and vasoreactivity abnormalities at the retinal microvascular level could be an early, non invasive and sensitive diagnostic marker of the RCVS at the first medical consultation in emergency.

Inclusion Criteria:

• repetitive thunderclap headache highly suggestive of RCVS (clinical syndrome)
• maximum delay of ten days between the first thunderclap headache (qualifying event) and patient's inclusion.
• informed written consent

Exclusion Criteria:

• intracranial aneurism on angiography (Brain MRI or angioscan)
• severe atheroma with cervical stenosis up to 80%
• medical history of diabetes and/or hypertension
• minor

male and female with Reversible cerebral vasoconstriction syndrome