I've been performing systematic self-tonometry as well as taking regular blood pressure readings for four months now. As Dave predicted I would, I've made several personal discoveries by simply gathering data and letting the findings rise to the top.
As one individual, my IOP is significantly influenced by environmental factors, particularly diet. This has been frustrating because it is all a matter of trial and error, although I have been able to short-cut the process somewhat by reading about the restricted diets of migraine sufferers and the like. In my case, free glutamates (MSG in all its various and sundry forms, in particular) will always spike my IOP by as much as 6 points. It takes about three hours after ingestion for the effect to register which then, unfortunately, lasts for some time. The same holds true when I eat foods that throw off histamines or tyramines. Both of these biogenic amines are derived from amino acids and produced by foods that are highly processed, fermented, aged, marinated, slow-cooked, or, even slightly, spoiled. Needless to say, when I go to bed with high pressures as a result of making a "mistake" at dinner, I pay for it with higher than normal IOP that night and into the next morning. My working motto when it comes to food now is: "Plain is good; fresh is best." Sometimes that's easier said than done...try eating sushi without soy sauce.
My dietary effect is consistent enough that I can predict it in advance or almost always find the missing link when I look back at ingredients I consumed or take note of the way the food was prepared.
My histamine and tyramine intolerance is nothing unusual in the world of migraine sufferers, as I mentioned. Also, people taking MAOIs have to be very careful about tyramine overloading which can lead to a hypertensive crisis. As for free glutamates; these occur in both natural and artificial states and are tricky to work around. The other side of the dietary effect for me, by the way, is fasting: if I skip meals, my IOP goes up. So, eating correctly is going to take some time to get figured out and implemented into my daily routine.
Another environmental factor I've observed--and one I mentioned in a reply to a recent blog post the other day--is the "darkened room effect." Measure your IOP immediately before and after going to the movies and see if your IOP hasn't increased dramatically.
Two others are ones most of us are already well aware of: to wit, mental stress and body posture changes. Winter weather is problematic as well (I live in the frigid Midwest) due to hormonal changes and the extended periods of darkness. My IOP is signficantly higher and more difficult to control since the onset of the winter season.
The above-mentioned factors have been scientifically researched by others but not necessarily in the context of glaucoma sufferers. To do your own research, try entering key terms used throughout this blog entry in your search engine.
On the positive side, I exercise six days a week in the early morning--both cardio and weight-lifting--and the downward effect on my IOP appears to be the equivalent of one dosage of drops. (In this regard, I currently take a daily regimen of Timoptic, Travatan, and Azopt.)
When all is said and done--and again, just as Dave predicted--what many ophthalmologists think is stable IOP is anything but. I'm having a very difficult time with nocturnal IOP, for example, and plan to tackle that in earnest next.
As a final thought: for those of undertaking this somewhat daunting endeavor of self-tonometry, I've found it best to let the data speak for itself and try not to force answers to problematic readings in an attempt to figure things out more quickly. Uncertainty is our friend in this case because it makes us look deeper at root causes and understand things more completely. Besides, it's not like our IOPs suddenly started behaving this way just because we can now observe them. In my case, at the age of 55, I can only imagine what my prior years' IOP readings would look like had I been taking them. The good news is that gluacoma in many cases gives us time to correct things because of its chronic nature. I, for one, would be sorely tested if my POAG condition were acute.