Resolution. If you're running at 4k, knocking it back to 1920 x 1080 will help some. That will work effectively because 4k is exactly 4 times the number of pixels as a 1920 x 1080 display, so it will do 4 pixels per dot instead of 1, making it bigger.
Well, to be precise, it's actually DPI. I actually got a lower res 32" monitor for my computer intentionally to make dots easier to see in FSO. My DPI is 49, and that seemed to be critical mass for my eyes to be able to spot dots easier. Any higher and I can't see them as easily. To get the same DPI with 1920 x 1080 resolution, it would need to be about 45".
Removing anti aliasing will help too, though it will make lines a bit jaggier.
Wiley.