Diurnal IOP

Thanks to new technology including home tonometers and contact lens sensors, monitoring intraocular pressure (IOP) around the clock is getting easier. But while circadian IOP fluctuation has been known for more than a century, what role does it play in glaucoma progression? And can monitoring it help guide treatment? In a playful boxing-themed debate, two heavyweight experts squared off over these serious questions at the Glaucoma Subspecialty Day of the 2019 ASCRS ASOA Annual Meeting in San Diego, USA. IOP VARIATION MATTERS Arguing for 24-hour IOP monitoring, Ike K Ahmed MD of the University of Toronto, Canada, presented a case of open-angle glaucoma progressing despite office-measured IOPs consistently in the mid-teens. Home tonometry revealed frequent late-evening spikes above 30mmHg in one eye and wide variations in both. Based on this additional information, Dr Ahmed performed a MIGS procedure to reduce peak IOP and fluctuations. “Measuring IOP only in office hours is highly likely to miss the patient’s peak pressure, which is where conventional thinking is where the damage occurs,” Dr Ahmed said. Studies suggest that peak IOP occurs between 9:30pm and 7:00am in 75% of patients, and detecting these higher pressures often leads to therapy changes. Wider IOP fluctuation is associated with greater risk of ocular hypertension progressing to glaucoma, higher risk of glaucoma progression and greater visual field loss, Dr Ahmed noted. Similarly, two large studies, the Collaborative Initial Glaucoma Treatment Study (CIGTS) in 2011 and the Advanced Glaucoma Intervention Study (AGIS) in 2004, found IOP fluctuation a stronger independent predictor of visual field progression than mean IOP. Dr Ahmed allowed that other large studies, including the Early Manifestation Glaucoma Trial (EMGT) in 2007, did not find IOP fluctuation a significant factor. However, this may be because the EMGT patients’ IOP was not as well controlled as in AGIS and CIGTS, suggesting fluctuation may be a bigger problem in treated eyes with lower pressures. Diurnal IOP variation can help determine how invasive a procedure is needed for patients progressing at apparently “normal” pressures, Dr Ahmed said. “If glaucoma is progressing at 12, are the pressures fluctuating or is it really progressing at 12? If they are fluctuating [into the high teens or more], we don’t need to aim for a pressure of 8, we may aim for 12 and have it consistent. “On the other hand, if someone has low teens and they don’t fluctuate much, that’s when we pull out the big guns like trabeculectomy” to achieve stable single-digit pressure. “It’s 2019. Let’s think of IOP of more than a single office measurement. Peak IOP and fluctuations are useful in glaucoma management,” Dr Ahmed concluded. IOP VARIATION IS NORMAL Arguing against diurnal monitoring, Douglas J Rhee MD of Case Western Reserve University in Cleveland, USA, noted that wide second-to-second IOP variation is normal, increasing nearly 10mmHg from position changes and up to 60mmHg in forced blinking. If IOP variation caused glaucoma, this physiological variation would make it much more common. Dr Rhee found the literature unconvincing. Only four published studies have examined circadian IOP fluctuation without an associated intervention, and all were retrospective comparisons that did not establish causality, he noted. In addition, several large studies, including the European Glaucoma Prevention Study (EGPS), EMGT and the Ocular Hypertension Treatment Study (OHTS), found no connection between progression and IOP variation. Perhaps more importantly, diurnal IOP variability increases with higher mean IOP, Dr Rhee pointed out (Zeimer RC. Ch 21, Shields, Ritch and Krupin. Mosby 1996). “Variation is just a marker for mean IOP.” However, inter-visit IOP variation is important because it often indicates a treatment failure that should be addressed, Dr Rhee said. Lastly, if IOP variation were the cause, trabeculectomy, which virtually eliminates it, would be curative, Dr Rhee argued. But it’s not, especially if it doesn’t achieve low pressure. “Too high is too high,” Dr Rhee concluded. And the audience agreed; Dr Rhee was judged to have won the debate.