This episode of the American Academy of Ophthalmology’s “Experts InSight” podcast features a conversational discussion among glaucoma specialists Dr. Andrew Pouw (host), Dr. Elyse McGlumphy, and Dr. Soshian Sarrafpour. Their primary focus is the challenging and often frustrating variability of intraocular pressure (IOP) and its implications for glaucoma diagnosis and management.
Understanding IOP Fluctuations
The discussion begins with the common patient question: “Why does my eye pressure vary so much?”
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Analogy to Blood Pressure/Glucose: All three doctors use the analogy of blood pressure or blood glucose levels, explaining that IOP is not a static number but naturally fluctuates throughout the day due to various bodily factors and activities.
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Patient Education: Dr. McGlumphy notes that this conversation often occurs during a follow-up visit, especially when a patient is concerned about a pressure reading that is higher than a previous one, despite treatment. Dr. Sarrafpour emphasizes the importance of engaging patients early on to make them aware of glaucoma’s fluctuating nature.
IOP Variability and Glaucoma Progression: The Literature
The conversation delves into the controversial topic of whether IOP variance itself is a risk factor for glaucoma progression, referencing several key studies:
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AGEIS Study: Initially suggested an association between IOP variation and glaucoma progression, especially in lower-pressure groups. However, subsequent post-hoc analyses diluted the strength of this finding.
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Conflicting Evidence: Dr. Sarrafpour highlights that studies like CIGTS have supported the idea that IOP fluctuation is relevant, while others (OATS study, European Glaucoma Prevention Study, EMGT, DIGGS) have not found a statistical association. This discrepancy is often attributed to study design limitations, such as inconsistent data collection (e.g., timing of diurnal curves).
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Collinearity: Dr. McGlumphy points out the significant collinearity between IOP fluctuation, mean IOP, and peak daily IOP, making it difficult to isolate variance as an independent risk factor.
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UKGTS: The UK Glaucoma Treatment Study (UKGTS) is presented as a more robust study that meticulously collected various IOP data points. It concluded that there is no association between IOP variance and glaucoma progression, at least in primary open-angle glaucoma. However, Dr. Sarrafpour adds a caveat that this might not apply to secondary open-angle glaucomas (e.g., pseudoexfoliation, pigment dispersion) which may exhibit greater fluctuations.
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Clinical Application: Despite the conflicting literature, clinical decision-making often boils down to the clinician’s and patient’s risk tolerance. If a patient with a normal tension glaucoma phenotype is progressing with fluctuating pressures, aggressive treatment (like trabeculectomy) might be considered, even if the direct causal link of variance isn’t definitively proven. Other contributing factors like hypoperfusion or sleep apnea are also considered.
Sources of IOP Variance Beyond Diurnal Rhythms
The doctors discuss various environmental and situational factors that can affect IOP:
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Yoga/Exercise: Head-down positions in yoga (e.g., downward dog) can significantly elevate IOP (10-20 mmHg increases), though relaxation-focused practices may reduce it. Certain exercises with head-down squatting can also cause spikes.
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Stress: Elevated stress levels can potentially increase IOP.
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Common Activities: Even seemingly innocuous activities like blinking (which can cause significant, albeit transient, IOP spikes) or squeezing eyes shut (can raise pressure to 50s mmHg) are acknowledged to affect IOP.
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“Live Your Life” Philosophy: Despite these potential impacts, the general consensus is to advise patients to live their lives as normally as possible. Significant lifestyle changes are only recommended in severe cases where every effort to preserve vision is critical. The doctors emphasize not letting the disease take away patients’ peace of mind.
The Challenge of IOP Measurement Devices
The conversation shifts to the variability introduced by different IOP measurement tools:
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Rebound Tonometers (iCare): Dr. McGlumphy shares her research and experience with the iCare tonometer. While not a perfect surrogate for Goldman applanation tonometry (agreement falls off at extreme pressure ranges), it’s easy to use and provides valuable data. The iCare HOME device is particularly useful for capturing extensive home data and identifying trends, saving patients from prolonged in-clinic diurnal curves.
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Reproducibility: The lack of reproducibility across different studies and devices is a recurring theme. Dr. Sarrafpour humorously notes that “the lack of reproducibility is the only reproducible aspect of things.”
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Holistic Approach: Despite imperfect tools, clinicians must work with the available data. Glaucoma management relies on integrating various “noisy” data points, including visual fields (subjective), OCTs (subject to artifact), and cup-to-disc ratios (fluctuating). The ultimate goal is to prevent progression, not solely to target a specific IOP number.
The Future of IOP Monitoring: Implantable Sensors
The discussion concludes with a look at future technologies for continuous IOP monitoring:
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Intraocular Implants: The European iMate IO sensor (a sulcus-based implant) and other developing technologies (contact lens systems like Triggerfish, suprachoroidal implants, other intraocular implants) hold promise for providing continuous, real-time IOP data.
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More Data ≠ Better Decisions: Dr. Sarrafpour expresses caution that while more data can be helpful, an abundance of “noisy” or highly variable data could lead to increased patient and physician stress without necessarily improving clinical outcomes. The ultimate goal remains preventing progression, not merely optimizing a pressure number.