1. Victor Horsley Department of Neurosurgery, National Hospital for Neurology and Neurosurgery, London, United Kingdom
2. UCL Queen Square Institute of Neurology, London, United Kingdom
3. Department of Neuro-Ophthalmology, National Hospital for Neurology and Neurosurgery, London, United Kingdom
4. Department of Statistical Science, University College London, London, United Kingdom
5. Headache and Facial Pain Group, National Hospital for Neurology and Neurosurgery, London, United Kingdom