The NHS study period began in 1980 and the HPFS in 1986 (when
we began to assess dietary habits) and lasted until 2008. A participant
began to contribute person-time in 2-year increments after age 40 (as
glaucoma risk increases after this age) and only during periods in
which they indicated having had an eye examination. Participants
contributed person-time from the return date of the first questionnaire
until the earliest occurrence of either a report of glaucoma, cataract
extraction (because it can be difficult to detect exfoliation material
after this surgery), cancer (because this diagnosis can profoundly effect
lifestyle behaviors), death, loss to follow-up, or 2008.