Usually, clinical IOP measurement is performed during the day; little is known about nocturnal IOP fluctuations in relation to glaucoma management 3. A recent surge of interest in nocturnal IOPs stems from the hypothesis that significant glaucomatous damage may occur at night4,5. In response, some investigators have advocated particular classes of glaucoma medications based on their nocturnal IOP effects6-8. The most efficacious drug on the market may not be the preferred treatment if it is ineffective at night. Therefore, the understanding of nighttime IOP and the aqueous humor dynamics that control it has important scientific, clinical, and commercial implications.