New observations noted about circadian IOP patterns

San Francisco - Both IOP and the rate of aqueous flow follow a circadian rhythm and that has significant implications for the evaluation and treatment of patients with ocular hypertension and glaucoma, said Robert N. Weinreb, MD, director, Hamilton Glaucoma Center, and distinguished professor of ophthalmology, University of California, San Diego.

Although previous concepts held that IOP peaks in the morning and so may be best measured at 8 or 10 a.m., more recent data from the evaluation of subjects in 24-hour sleep laboratories indicate that IOP is highest during the nocturnal period both in healthy individuals and patients with glaucoma. Studies of aqueous flow show that it is disproportionately represented during the day and decreases at night. Aqueous flow during the 8 hours from 10 p.m. to 6 a.m. accounts for only 17% of the day’s total, noted Dr. Weinreb.

Those findings may be expected to have important clinical implications considering that the various types of drugs used to treat glaucoma have different mechanisms of action with respect to effects on aqueous humor production and uveoscleral outflow. Supporting that hypothesis are the results of various studies that show timolol dosed in the morning was highly effective during the day but was less effective at night, while latanoprost (Xalatan, Pfizer Ophthalmics) offers effective IOP control around the clock.

“Based on the studies performed so far, it seems that a single measurement of IOP during usual office hours is insufficient for optimal glaucoma management,” Dr. Weinreb said. “We need to consider measuring IOP at various times throughout the day and measuring it in the supine position, which seems to give a better estimate of peak IOP than sitting IOP.

“In addition, if peak IOP occurs during the night, it seems likely that a lot of glaucomatous damage also occurs in the nocturnal period and we need to be using medications that are effective at lowering IOP during the night,” Dr. Weinreb said.