[1] Univ Western Ontario, Schulich Sch Med & Dent, Dept Epidemiol & Biostat, London, ON, Canada
[2] Univ Western Ontario, Schulich Sch Med & Dent, Dept Paediat, London, ON, Canada
[3] London Hlth Sci Ctr, Childrens Hosp, Clin Neurol Sci, London, ON, Canada
[4] Univ Western Ontario, Schulich Sch Med & Dent, Dept Ophthalmol, London, ON, Canada