Well, I started out fairly clear in my own mind about eye exercises. I'm now totally confused.
About 2 years ago, I mentioned a 20 year old (ish) article in a well known science magazine. It showed micrographs of the human lens and good drawings of the fibrous / muscle supports to the lens. To my dismay, it clearly showed the anchor points on the lens moving inwards with age. This meant that any attempt to strengthen them was futile. At about this time, Mrs R started reading "Better sight without glasses" and found that she was having the first signs of shortsightedness...about halfway through the book! About the only interesting thing about that book was the hint of old English in its prose.
You need to take on board the point raised by a professional earlier in this thread. Roughly speaking, the lens only fine tunes the settings we are blessed with.
Any exercise is good, but all things in moderation. However, I am personally convinced that some people can correct focus by manipulating the large muscles that move the eye. They do in effect, distort the whole eye. I know I do this. The problem is, that this can cause all sorts of eye spasm and resulting pain in extraordinary circumstances. As an aside, it's worth mentioning that I'm sure that my ability to do this stems from early childhood, and a morbid fear of blindness. Rare, but I know I'm not unique.
What I'm trying to get across, in rather a long winded manner, is that in doing these exercises, one can not be sure which muscles are being tugged at. I quite quickly learned to correct for a rather disappointing cataract operation. The - 1.5 can be hauled into sharp focus on demand, and
I'm certainly not reforming the shape of my lens--since it is man made. (Actually, that's not quite true, but the range that I can effect is minute.)
To sum up. By all means go a tad shy of prescription if you feel that this will help, but not for long. Muscles need rest and eyes are no different in this respect. The looking up from the screen to infinity many times a day is a good scenario. If you do not have a window onto infinity, then that is the time to wear the exercising prescription...just for a few moments, then back to the restful lens.
There is essentially no difference to going to the gym, and overdoing it for hours. Gentle stretching and rest is best.