title: Reply.
authors.affiliation: King's College London, Twin Research and Genetic Epidemiology, St. Thomas Hospital, London, United Kingdom.
authors.forename: Katie M
authors.initials: KM
authors.lastname: Williams
authors.affiliation: King's College London, Twin Research and Genetic Epidemiology, St. Thomas Hospital, London, United Kingdom. Electronic address: chris.hammond@kcl.ac.uk.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hammond
mesh_terms: D004522:Educational Status; D005062:European Union / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000453:epidemiology*