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Why is IOP fluctuation important?
Your eye constantly makes aqueous humor, a clear liquid produced in the front of the eye. As new aqueous is produced, the same amount should drain out through the “angle”. This process keeps the pressure in the eye, the IOP, stable and fairly constant. If the drainage angle is not working properly, fluid builds up. Pressure inside the eye rises, damaging the optic nerve which can lead to loss of vision and eventual blindness if left untreated. Currently the only way to manage and treat glaucoma is by lowering the IOP. IOP is the main recognized and treatable risk factor for glaucoma.
IOP is currently monitored in-office during isolated daytime measurements. Current glaucoma management includes measurement of IOP every few months, between the hours of 8AM and 5PM, even for patients with severe disease. Treatment decisions are often based on these individual snapshots in time of a single IOP reading. However, we have long known and recognized that critical values of IOP fluctuate throughout day and night day-to-day (short-term), and over months to years (long-term). Knowing that IOP, as the only modifiable risk factor for glaucoma disease progression, can fluctuate, has motivated development of better ways of capturing IOP variability during the day and night.
Studies have shown that day and night IOP rhythms fluctuate, with spikes often occurring outside of office hours. In studies of IOP measured around-the-clock in hundreds of patients, peak IOP can occur morning or night. Missing these peaks in measurements can result in misdiagnosis and under-treatment. In addition to spikes in IOP, wide fluctuations in IOP have also been believed to contribute to progression of glaucoma.
Factors affecting fluctuations in IOP are believed to include such things as position, sleep patterns, exercise, hormone levels, and even medications. IOP generally tends to be higher when lying flat and during the night. IOP may potentially be modulated by other health conditions such as low and or high blood pressure and sleep apnea. Variations in many of these factors, as well as others that we do not yet know, may be contributing to daytime and nighttime variations in IOP which can have relevance to optic nerve health.