Is there an average of how much IOP can increase during sleep compared to average day pressures?
The original question from the FitEyes email group was:
Is there an average of how much IOP can spike during sleep compared to average day pressures?
I can answer this three different ways:
1. What is the commonly reported increase in IOP during sleep compared to the baseline daytime IOP?
The answer is roughly 5mmHg.
2. For a glaucoma patient, what is the safe increase in IOP during sleep compared to the baseline daytime IOP?
This depends on whether the patient is experiencing glaucoma progression, as well as many other factors. See #3 below for further thoughts.
3. What is the actual observed increase in IOP (from lowest to highest) in real life life among well-controlled glaucoma patients who are performing self-tonometry with a highly accurate tonometer?
The observed range is about 10mmHg. Of course, it varies by day. All the people in this group experienced at least one day (typically several) during this study with an even larger diurnal range.
We call this range the diurnal curve. The expected diurnal range is about 5mmHg. But in this study, which has better methodology than most published studies I have reviewed, the range was found to be 10mmHg.
It is common for the peak in the curve to happen during sleep (typically the early morning hours). Many FitEyes members have found that if they check their IOP upon awakening and before activity (even before getting out of bed or sitting up), the result given in this measurement is substantially equal to the highest value seen during the night.
With that background, I will provide a longer answer.
Ultimately, we are not talking about just sleep. When you are not sitting upright or standing, your IOP will be higher. It an unavoidable fact, and an expected physiological response.
If you bend forward, lie down, or do a headstand, your IOP will increase. Along with this, other things change too (CSFP, BP, etc.). We have a (good) stress response every time we stand up. If we did not, we would be at risk of passing out. Something as simple as changing our posture can involve complex physiological changes. For the most part, these changes balance each other out and are not harmful.
Therefore, we should expect a higher IOP during sleep. It's normal. Healthy people without glaucoma experience an increase in IOP while lying down and/or sleeping. An increase of 5mmHg is not unusual. It is also not harmful to someone with normal eyes.
It's unclear whether a certain IOP increase while sleeping is harmful to most glaucoma patients. In some patients your GS may indeed consider it to be harmful. But it is not harmful to normal eyes and it may or may not be harmful to a majority of glaucomatous eyes. Most of the scientific studies I have seen on this topic have had flawed methodology.
The increase in IOP while lying down can be offset by an increase in perfusion (blood flow) to the optic nerve. We also do not yet fully understand the dynamics of the changes that happen with different postures. People who do headstands, for example, experience a doubling of their IOP while inverted, yet they do not have increased risk of developing glaucoma. Is this because all the other pressures increase proportionally with IOP while inverted?
In cases where an increase in IOP while sleeping is indeed a problem, is it really because of circulatory or perfusion issues?
I cannot speak for the whole ophthalmology profession, but from my perspective as a patient, it seems the assumption within the profession is that any IOP increase at night is problematic for every glaucoma patient. While it is certainly true in some cases, it does not appear to be a valid assumption in other cases. To back up that statement, here are some details of the FitEyes study I mentioned above.
Among the FitEyes community of users with Reichert 7CR tonometers, members whose glaucoma is well-controlled (and not progressing) saw an increase of 10mmHg or more. Specifically, they could expect a day (24 hour period) where their highest IOP was 10mmHg or more above their lowest IOP. They would not see the 10mmHg diurnal range every day, but that diurnal range would not be unusual on a monthly basis for anyone in this group.
The 10mmHg value I'm citing is an average across all subjects and all days for which we had valid data after an adjustment to remove extreme values. To compute this average, the extreme diurnal ranges for each subject were first eliminated. Then a mean was computed for the largest diurnal range across all subjects. It is very important to note that the extremes did not represent bad data. There was no statistical reason or methodological reason to eliminate these data. We simply chose not to report a maximum value. The data could be re-examined and we could report a maximum diurnal range inclusive of all valid data and that value would be larger than 10mmHg.
In almost no cases among this group was the diurnal range as narrow as reported in the literature (e.g., 5mmHg or less). This is an unpublished study.
I believe the range in this FitEyes group is higher than the commonly reported diurnal range because this is real-life home monitoring where we can capture all the effects of life (from stress to exercise to anything else). In other words, I believe that the more the research begins to take advantage of newer technologies which allow better monitoring of real life IOP, the more we will see higher highs and lower lows -- thus larger diurnal ranges being reported.
Nonetheless, currently this is a surprising finding to most ophthalmologists. Ophthalmologists would tend to be alarmed by a 10mmHg diurnal range because they would assume it predicts glaucoma progression. However, among this group there is no greater progression than what is expected for glaucoma patients in general.
Coming back to the question:
What is the actual observed increase in IOP (from lowest to highest) in real life life among well-controlled glaucoma patients
My answer 10 mmHg. If you see your highest IOP 10mmHg higher than your lowest in a given 24 hour period, you are not alone. You don't have to conclude that this is an emergency. Your doctor may be surprised (even shocked) but the FitEyes data show this to be a fairly common occurrence. Is it ideal? Probably not. But it is the reality and it doesn't necessarily mean more aggressive treatment is needed. The determination of that should be made after careful consideration with a glaucoma expert, ideally one who has a lot of experience with real-life IOP fluctuations.
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Thank you! I'm about 10 up on average during sleep so I won't panic and sleep better now for knowing this!