I wear bifocals and started to spend a lot more time at the computer at home when I retired. I would sit there and read email for a few minutes and maybe Google a couple of things to learn something I was curious about when I was still working. I had a job where I worked with my hands, and I only had to use a computer to set some settings for a CNC machine we used in the shop. I usually used the old machines and lathes were all of the adjustments were manual. A chiropractor in Sacramento ended up being on my to-do list shortly after I retired. Here is how I caused my neck a lot of unnecessary pain.
If you wear bifocals, you know that you need to look out of the bottom of your glasses to read things such as a newspaper or the instructions for a can of soup you are about to heat up. It is easy to just hold an object you want to see clearly or to adjust something in your hands that you are trying to read through bifocals. It is a mix of tilting your head and moving what it is you are trying to see. However, when it comes to computer monitors, you are just tilting your head back to be able to see out of the bottom of your glasses when you are looking at the screen. That was what made my neck sore to the point of impinging on a nerve that caused shoulder pain for me.
I was tilting my head back for long periods of time trying to read the screen through my bifocals. If you are going to sit at a computer and you wear bifocals, you need to get a pair of glasses that have the magnification part across the entire lens. That way you do not have to tilt your head back to see the screen. I learned that a little late, and I had to have adjustments and therapy on my neck to stop the nerve pain. Now I have regular glasses for use just at the computer, and no more neck pain.