Episcleral venous pressure remains unchanged throughout day, study finds

PARIS — A study examining the impact of episcleral venous pressure and other factors on circadian changes found that episcleral venous pressure did not vary from night to day, while aqueous humor flow rate decreased by almost 50%.

In addition, sitting IOP was slightly lower than aqueous humor flow rate, supine IOP was unchanged, and outflow facility and uveoscleral outflow decreased significantly at night, according to a poster study presented by Arthur J. Sit, SM, MD, and colleagues at the World Glaucoma Congress.

"Decreased aqueous humor flow at night is compensated by decreased outflow facility and uveoscleral flow to maintain a high IOP. [Episcleral venous pressure] remains unchanged, which suggests active regulation," Dr. Sit and colleagues said.

The study, which included 42 eyes of 21 healthy subjects, examined the mid-diurnal and midnocturnal periods. IOP, aqueous humor flow rate, outflow facility, episcleral venous pressure and uveoscleral outflow were measured and compared.

The researchers used a custom computerized venomanometer to measure episcleral venous pressure. The objective test works by applying an inflatable chamber to an episcleral vein to determine the pressure measurement needed for collapse, according to the study.

Disclosure: Dr. Sit and colleagues have no relevant financial disclosures.