This would be a better question posed to your eye doctor. Are you receiving annual checkups? A family member had similar issues, she had developed astigmatism and her brain was trying to compensate.
That said:
Resolution itself is likely not the deciding factor on eye health/strain. I personally dont feel any difference on any screen I look at strictly in a resolution sense. Different screen brightness, viewing distance, ambient light, length of use, media displayed, etc all play a much larger role.