RT Journal Article SR Electronic T1 CORRESPONDENCE JF British Journal of Ophthalmology JO Br J Ophthalmol FD BMJ Publishing Group Ltd. SP 220 OP 220 DO 10.1136/bjo.21.4.220 VO 21 IS 4 A1 M. Tree YR 1937 UL http://bjo.bmj.com/content/21/4/220.1.abstract AB