[1] Univ N Carolina, Dept Epidemiol, Chapel Hill, NC 27514 USA
[2] Johns Hopkins Univ, Dept Epidemiol, Baltimore, MD USA
[3] Univ Mississippi, Med Ctr, Dept Med, Jackson, MS 39216 USA
[4] Univ Wisconsin, Dept Ophthalmol & Visual Sci, Madison, WI USA
[5] NEI, Div Epidemiol & Clin Applicat, Bethesda, MD 20892 USA
[6] Natl Univ Singapore, Singapore Eye Res Inst, Singapore 117548, Singapore