RT Journal Article SR Electronic T1 Case–control or cohort study? JF British Journal of Ophthalmology JO Br J Ophthalmol FD BMJ Publishing Group Ltd. SP 1175 OP 1175 DO 10.1136/bjo.2011.203141 VO 95 IS 8 A1 Tamhane Ashutosh A1 Gerald McGwin YR 2011 UL http://bjo.bmj.com/content/95/8/1175.1.abstract AB