Hi- I am Dr. Lewis and it sounds like what your are experiencing is most definitely accomodative spasm. I have seen multiple cases like yours and the reason you are not getting good answers is because this is not a common condition.
First, let me say that the problem tends to occur in people who are type A personalities, and very well keyed into their medical health. Listening to your explanations of what you perceive is happening is interesting but you are not one hundred percent correct in your understanding of accomodative spasm.
I think I am grasping from your explanation that you have been refracted to a -3.50 sphere. This doesn't necessarily mean that this is the correct prescription for your eyes, more likely it is what you have manifested on refraction
it would be very important to obtain a cycloplegic refraction or streak retinoscopy to determine what your true refraction is in your eyes. My guess is that it would be close to plano or -1.00. That would mean that you are holding and accomodating about 2.00 diopters of myopia
and this is why you are getting very bad headaches and straining with a loss of focus. You could even possibly be hyperopic and pulling in even more myopia with your ciliary muscles.
You asked for an answer to each question.
1. You feel your inability to focus is due to something other than your tensed muscles. Wrong. Accomodative spasm means that you are holding tension in your muscles even at distance. When you then try and focus up close, you use even more muscle power and you basically over strain your accomodative muscles and they tank out. If your accomodative complex was functioning normally, you would be holding no muscle contraction at distance and only using a small amount of muscle contraction at near. You are just in hyperdrive with your muscles. Putting in the muscle relaxing drops will tank your near vision completely so you can only see at distance. But even at distance you might be blurry for a while because you have trained your brain to see only well when you accomodate (even though it's not necessary). By doing this, you will have no muscle power to bring the focus in up close at all so the cycloplegic drops will cause your vision for a few days to be extremely blurry, at distance and especially up close. The only thing the drops should do is relieve the headache. Not the blurry vision
2. You say that to obtain clear vision, it does not seem like you are relaxing but overstraining. This is typical for accomodative spasm. Your muscles have been in a constant strained state for such a long period of time that your brain does not know what to do. It keeps trying to do what it normally does to bring in focus - pull in muscle power. This doesn't work because the muscles are already overworked. It just makes the problem worse. To fix the problem, you need to complete paralysis or cycloplegia of the muscles for about a week. Along with this you might need a small amount of prescription for distance(for you it would be probably be only just astigmatism) and then use some cheater glasses
up close to keep the muscles from needing to accomodate at all. You start with a +2.50 cheater pair of glasses to read with and a +1.50 for computer. Over a few weeks work your way down to less and less power. If the symptoms come back you go up on the cheater power. Over the counter glasses are cheap. You can go back and forth for a while to find what makes the vision clearest and gives the least headache. Finding the right strength will obviate the need for any accomodation.
3.You are confused because dilation makes your distance vision blurry too. This problem is short lived and is occurring because your brain is dishabituated to your real prescription at distance. You have gone so long in an accomodative state at distance that when accomodation is relaxed, you can't even see far away. This problem will go away after a week or so of cycloplegia because your brain will rehabituate to your normal non-refractive clear vision state. It takes time and doesn't happen right away.
So what I have told you is confusing but here is the botXXXXX XXXXXne.
Put in cycloplegic drops (preferably long acting like atropine or homatropine). Leave them working for two or three weeks. Remain blurry at distance for a bit and attempt to correct the distance with only a little astigmatism correction or slight hyperopic correction if your cycloplegia reveals hyperopia. Whatever your best cycloplegic refraction is, even if it's a little blurry, this is what you should wear for distance.
Buy a pair of over the counter +2.50 glasses for near work/reading and a pair of +1.50 glasses for the computer. Use them any time you need to read or use the computer.
After 2 weeks, stop the cycloplegic drops and see if your distance has improved to clarity. It should. Continue to use the close glasses for a few more weeks so you do not accomodate at all.
Gradually over weeks or months, go down on the reading and computer glass strength reading +1.50, computer +1.00.
Then eventually eradicate the cheater glasses.
This will allow the muscle strain to gradually abate.
The only caveate to this is your age. Nowhere does it state how old you are. If you are over forty, do not get rid of the reading or computer glasses at all. Any attempt to go without them will kick you back into accomodative spasm.