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.