[1] Kings Coll London, Kings Coll Hosp, NIHR Wellcome Trust Kings Clin Res Facil, Dept Basic & Clin Neurosci,Headache Grp, London, England
[2] Univ Bern, Bern Univ Hosp, Dept Neurol, Bern, Switzerland
[3] Univ Utah, Dept Neurol, Salt Lake City, UT USA
[4] Univ Utah, Dept Ophthalmol, Salt Lake City, UT USA