[1] Univ Nottingham, Acad Ophthalmol, Sch Med, Nottingham, England
[2] Queens Med Ctr, Dept Ophthalmol, Nottingham, England
[3] Massachusetts Eye & Ear, Dept Ophthalmol, Boston, MA USA
[4] Harvard Med Sch, Boston, MA 02115 USA
[5] Singapore Natl Eye Ctr, Dept Cornea & Refract Surg, Singapore, Singapore
[6] Singapore Eye Res Inst, Singapore, Singapore