Not posture related. Can be in completely relaxed position. Reclining in a chair with neck totally relaxed.
However focusing on the screen causes pain in the back of my neck which gets worse rapidly.
Does anyone else experience this, or a variant of it?
I don't know if this is related to any technology issues but for sure I only get the pain when viewing screens.
degen Not posture related.
Not entirely convinced just yet. If you generally have bad posture, issues can crop up at unexpected times, like being a relaxed position. Overuse of upper traps and subsequent neck pain is extremely common in physical therapy 
The best way to fix that and prevent it is simply awareness
You can also try and simulate a similar setup by reading a book in a similar position and see if that triggers anything. If it only happens when you're looking at a screen, then maybe there is something. But look into the most likely culprit a little more first 
On me those muscles are very tight and filled with trigger points. I think the eyes are very related to posterior neck muscles. Put your hand on your suboccipital muscle region and you can feel the muscles contract when you move your eyes.
I will work on freeing up my posterior neck and upper back and see if it makes a difference. I didn't want to confuse the forum with my RSI complaints but there seems to be a connection between migraines, eyestrain and neck pain and I'm really not sure if technology plays a role.
Thank you
Put your hand on your suboccipital muscle region and you can feel the muscles contract when you move your eyes.
O_O weird.
It's very well known that migraines (and light sensitivity) is connected to neck pain. It's surely not only you noticing it. I've noticed that myself, too. The reason is pretty much what you said -- the muscles are in a way or another connected, so if one gets inflamed, others will too. It's the same thing when I have hay fever in the Spring, I always know I will get toothaches too. The reason is my nose and respiratory system will be irritated, and that affects the upper part of my mouth too.
I didn't mean to lay claim to discovering these links (although it sounds that way), but only that I'm investigating how they affect my functioning specifically.
While the research and medical literature is rich with studies pertaining to these links, most doctors still try and treat the problem piecemeal.
Go see a chiropractor. Seriously. These problems need systemic treatment. A good chiropractor (get recommendations) will address both spinal and muscular issues. Mine realigns my spine with traction and adjustments, and provides me with substantial exercises to work muscles that normally are anemic.
degen On me those muscles are very tight and filled with trigger points.
Check into a outpatient Physical Therapy clinic* or follow Gurm's advice
There's no physiological connection between eye muscles and extensor neck muscles as far as I know. But that's just a direct connection, it's not a far reach from being affected by PWM (for example) and tensing up because of that.
*(I work in Physical Therapy so small bias)
fakeaccount migraines (and light sensitivity) is connected to neck pain.
It is, generally though neck pain or tightness triggers the headache. But being tense because of a headache could cause the reverse..
Gurm You need to add a caveat to that. They should not mess with the neck of random people, it's too big a risk. I speak from experience, I used to see one for problems I was having with my arms and stuff. He knew I didn't want neck work, but one time time had passed and maybe he forgot, but decided he would try neck work. I tensed up and he tried forcing it anyway. Did not have a good reaction to it, and have had discomfort for years since in my right ear. Maybe it's a pinched nerve, maybe it's something else. But I didn't have that problem before his undesired help. It is the same thing with other things, they don't have to live with the consequences of whatever, you do. Sure recommend them, but if the person doing the work is a stranger, and the person receiving the work is a stranger, then it's good advice to say no neck work.
Yoga, which I need to try, might help. Most people won't care for it because it's not a quick fix, it's a years long practice, but given that it works on soft tissue, if you stay with it, you should be limber and flexible, and you don't have to pay someone to do it for you. Maybe it'll unpinch or unblock my neck or whatever went wrong with it, who knows.
Slacor, if they're a reliable and reputable individual (and I'd search for one who is an actual DOCTOR) then they won't do unnecessary neck work. Mine opens up my neck and back as a matter of course, but he didn't the first time I went, and wouldn't have at all if I were unwilling.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4427187/
"Since eye lens accommodation is driven by activity in the ciliary muscles, a direct parallel change in trapezius muscle activity due to changes in eye lens accommodation could hypothetically involve the ciliary muscles. When clear vision is acquired an efferent signal is sent to the ciliary muscles to alter the refractive power of the eye lens; a copy of this signal could be sent to the trapezius muscles and/or other muscles in the neck/shoulder area in order to stabilize gaze (cf. [11])."
fakeaccount This. This. This. I also get toothaches in the spring when I have hay fever.
degen Same thing is happening to me. Did you find out what the issue was? Or how to alleviate it?
