better to proofread in paper?

At times, indeed, it could be dreadful, but proofreading is something writers must do in order to make their writing truly shine. Proofreading using a computer can be a real eye-straining experience. Spending hours staring at text can even do real harm to our eyes, and for some people, proofreading using a hard copy or printed page can be a lot easier and less tiring. For some, however,it is a matter of preference. Some editors find they can work better with paper, while others insist they can only work with PC monitors. I used to do my proofreading on paper until one of my former employers implemented online editing. I eventually got used to it, and now that I am a work-at-home writer-editor, I decided to stick with it.

As an ex-professional proofreader, I can assure you that it is very hard to check your own work. The eye sees what it wants to see, and often your own mistakes are overlooked. Printing a copy is the only really effective way of checking work. You also need to read every word slowly and carefully to avoid common mistakes that the spellcheck won't catch. Yes, it is tiring, but worth it when you know you have given it your best.

I usually edit a document once and then leave it until the next morning. With fresh eyes and forgetting everything I was trying to write, I can edit it pretty well.

Print stuff are always better for the eye. I'd actually advise you to make the surroundings a bit darker, sometimes the white on the monitor can be too harsh-like no artificial lighting if possible.

There is no better way than proofreading on the monitor. I think there is some problem with your eyes. Why don't you get your eyes checked? I write for hours nonstop using the monitor. As I wear glasses I find no problem. Good luck.