I understand that for each -1 diopter we get, the eye is lengthened by a millimeter.
An aside from personal experience:
I was able to reverse some diopters by learning to relax my inner eye muscles. I dropped my prescription in both eyes by 1.25. Basically, you open your eye lids wide open and a sympathetic muscle reaction can help your stressed eye muscles relax a bit, letting you focus just a little further away.
For me, I bought glasses that subtract off my contacts’ prescription, to view things up close without causing eye stress. You can practice the eye muscle relaxing with or without correction. However, if you improve, you need to further back off your prescription. So if I had eyes at -3.00 diopters, I would use reading glasses to add back what I needed to make it just barely blurry at the distance I normally use up close. I have glasses that net me -1.25 diopters as I improve, by increments of 0.25 diopters.
I just had the first worsening since my “fix” four years ago, so I am back to relearning how to relax my eye muscles, yet again.
I’ve used the soft bifocal contacts for many years now. My eyes have generally stayed at the same prescription or gotten stronger over that time. Since cataract surgery in 1 eye (which no longer needs correction) I am wearing 1 bifocal contact, with the prescription in that eye holding steady for many years now. I can function just fine with no correction at all in a pinch. For young people it’s definitely worth doing if you can (not everyone is a candidate).