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.