Concordance of aqueous humor flow in the morning and at night in normal humans.

PURPOSE To test the hypothesis that an individual shows concordance of aqueous humor flow in the morning and at night in a prospective inpatient fluorophotometry study in healthy subjects. METHODS Flow was measured in each eye every hour between 8 AM and noon and every 2 hours between midnight and 6 AM. Morning and nighttime flows were analyzed for differences between eyes and for differences between these two time points. Concordance of individual morning and nighttime flows were studied by categorization into low, medium, or high tertiles, dot plot, and ordinary least-squares regression (OLS) scatter plot. RESULTS In 28 subjects, the flow was similar between eyes within a subject with healthy eyes. In the one eye examined in each subject, the average flow was 3.12 +/- 1.09 muL/min in the morning, which decreased significantly to 1.59 +/- 0.58 muL/min at night. During each time period, the individual flow data were normally distributed. Concordance of an individual's morning and nighttime flows was 68%. A scatter plot of morning versus nighttime flows also supported concordance with an OLS regression fit of r(2) = 0.45. CONCLUSIONS The results provide evidence that aqueous humor flow is similar between eyes, that flow variation shows a normal distribution, and that individuals show a concordance of flow in the morning and at night. These observations support the posit that aqueous humor flow, which is a factor that contributes to the important clinical risk factor of IOP variation, is amenable to study as a quantitative trait.