Outflow facility has minimal decrease at night

SAN FRANCISCO — Outflow facility does not decrease enough at night to compensate for decreased aqueous humor flow rates in healthy young adults, according to a physician speaking here.

Arthur J. Sit, MD, presented the results of a study he performed with colleagues evaluating circadian variations in healthy young adults at the American Glaucoma Society's annual meeting. The study included 17 subjects aged 22 to 39 years who maintained a sleep log, wore a wrist actigraph for 1 week and were measured at the Mayo Clinic General Clinical Research Center over an 18-hour period.

Dr. Sit and colleagues found that outflow facility, as measured by tonography, changed by only –0.04 ± 0.02 in the nocturnal period. The change was not significant enough to compensate for the decrease in aqueous humor flow rate, which had a change of –1.34 ± 0.15, he said.

Using the Goldmann equation, a decrease in facility of about 50% is necessary to produce the measured IOP, if all other parameters remain constant, Dr. Sit said

"We can conclude that tonographically measured outflow facility does not decrease enough at night time," he said.