How 24-hour IOP measurements vary with glaucoma treatment

Clinicians should take into account the way IOP varies over the course of 24 hours depending on the glaucoma treatment used, according to the authors of a new literature review.

“We need to check pressures more often than once, outside the ‘office hours’ and if possible at night when patients are asleep,” wrote Anastasios G.P. Konstas, from 1st University Department of Ophthalmology, Aristotle University of Thessaloniki, Greece, and colleagues. They published their finding in Advances in Therapy. 

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While randomized controlled trials show that reducing IOP reduces the rate of visual loss in most glaucoma patients, researchers have too often assumed that a single daytime measurement provides an adequate understanding of whether a patient’s IOP is under control. Most clinicians only measure IOP during patient visits about every three months.

A single IOP measurement only indicates what is happening for 1 out of 1439 minutes per day, they noted. Other trials have shown that the efficacy of a given therapy can vary over the course of this time. As a consequence, clinicians may not be making the best choice about whether to use surgery, laser, or medication.

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Twenty-four-hour monitoring would reveal the true peak IOP and the level at which damage occurs, allowing an optimal level to be set for each patient, the researchers wrote. However, such constant monitoring is not yet possible for most patients.

The researchers analysed randomised controlled trials to see how IOP measurements varied over 24 hours with each therapy in hope of providing information clinicians can use to guide their treatment plans.

Normal fluctuations

IOP normally fluctuates throughout the day by around 4-6 mm HG, Konstas and colleagues found. In patients with ocular hypertension (OHT), the 24-hour fluctuation usually averages 6-8 mm Hg, but sometimes reaches 15 mm Hg. In glaucoma patients the 24-hour fluctuation usually ranges from 6-15 mm HG, but can reach as high as 40 mm Hg, they reported.

In most studies, IOP in untreated glaucoma is highest between 6 a.m. and noon; the authors noted the highest IOP in their own patients at 10 a.m. This time can also vary with the patient and type of glaucoma, they noted.

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For example, one study found that 45% of patients with exfoliation glaucoma (XFG) and 22.5% of patients with primary open-angle glaucoma (POAG), reach peak IOP outside office hours.

The patient’s position can affect IOP as well; in general, a patient’s IOP is lower when sitting than when lying supine, the researchers reported.

Among the findings from various medication studies they identified:

• The combination of dorzolamide and timolol was more effective than timolol alone in lowering daytime IOP, but not nighttime IOP.

• Latanoprost was more effective than either timolol or dorzolamide overall, and the reduction in IOP it caused seemed relatively uniform over the course of 24 hours in patients with POAG.

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• Timolol was more effective than dorzolamide at 3 p.m., but dorzolamide surpassed the effectiveness of timolol at midnight and 3 a.m.
• Supine IOP was lower with timolol than with latanoprost at night. Administering latanoprost, or latanoprost and timolol together, at night lowered daytime IOP more than administering the drugs in the morning.

• Latanoprost caused a significantly better 24-hour drop in IOP while tafluprost provide a significantly lower 24-hour IOP fluctuation.

• IOP reduction was greater with latanoprost and dorzolamide than with latanoprost at nighttime.

• Bimatoprost was as effective as latanoprost/timolol fixed combination in maintaining 24-hour IOP in patients with glaucoma or ocular hypertension in patients who switched from the unmixed combination of latanoprost and timolol.

How laser trabeculoplasty affects IOP

Less is known about the relationship of laser trabeculoplasty to circadian characteristics of IOP. Still, a handful of studies have produced interesting results, among them:

• In previously untreated POAG patients, circadian IOP fluctuation decreased from 7.9 mm Hg at baseline to 3.6 mm Hg 5 years after argon laser trabeculoplasty. In medically treated POAG patients, fluctuation decreased from 7.7 mm Hg to 5.8 mm Hg.

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• In glaucoma of an unspecified type, argon laser trabeculoplasty decreased fluctuation by 25%.

• In open-angle glaucoma whose target IOP was not reached with medication, argon laser therapy meaningfully decreased nocturnal but not diurnal IOP. (This finding conflicted with other studies.)

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• Selective laser trabeculoplasty reduced fluctuation by 46% while latanoprost reduced fluctuation by 64% in patients with POAG or ocular hypertension.

• The amplitude of 24-hour fluctuation was significantly reduced with selective laser trabeculoplasty in patients who had washed out of their topical medication therapy.

IOP fluctuations following trabeculectomy

A variety of studies have also examined 24-hour fluctuations in IOP following trabeculectomy. Some of the findings:

• IOP ranged by 4.8 mm Hg between 8 a.m. and 6 p.m. in patients with open-angle glaucoma treated with trabeculectomy.

• IOP ranged 10-17 mm Hg in patients who underwent a trabeculectomy with adjunctive 5-fluorouracil versus 14-22 mm Hg in patients who had a trabeculectomy without the antimetabolite.

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• In a group of patients with unspecified glaucoma, diurnal fluctuation of IOP was significantly greater among those treated with medicine than in those treated with trabeculectomy, even though the difference in mean IOP was not significantly different.

• In patients with advanced open-angle glaucoma matched for daytime IOP at 10 a.m., those treated with trabeculectomy had a significantly lower mean IOP, peak IOP and fluctuation in IOP than those treated medically.

• In patients with POAG who took a water-drinking test, mean diurnal IOP was lower with trabeculectomy or deep sclerectomy with collagen implant (DSCI) compared with latanoprost monotherapy, but the fluctuation was similar regardless of therapy.

The authors concluded by describing a novel wireless telemetry sensor for monitoring IOP in POAG, consisting of a silicon contact lens with a micro-electromechanical system (Sensimed AG). They noted a recent study finding that the device did not correlate Goldmann IOP readings, and did not detect differences in IOP between sitting and supine positions.

They called for new technology to make continuous monitoring feasible for everyone whose IOP is being treated.

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