Refresh rate is one thing that can cause eyestrain however in your environment, you are likely to find several things that can cause eyestrain, including glare on walls and reflections on the computer screen itself. Minimizing reflections and reducing ambient light are particularly important aspects of your physical-viewing environment. When your monitor power is off, it may surprise you to find that one of the reflections that you see is your own! In order to minimize reflections of things in front of your screen other than lights - including your own face - it helps to reduce the general light level (ambient illumination). Use window shades, blinds, or drapes to block out excessive sunlight, also reduce the internal ambient light if outside light cannot be reduced. Use proper lighting, overhead fluorescent lights tend to be an excessively bright source of ambient illumination, in addition to facilitating reflections. Reduce the lighting by using fewer light bulbs or florescent tubes or use lower intensity bulbs and tubes. I recommend using indirect lighting with a dimmer control, such as stand up halogen lamps that reflect light off the ceiling.
Once you have your environment set up, reduce the contrast setting of the monitor. Resist the temptation to run your monitor too bright. White should be a pleasant white, it doesn't have to illuminate your room. Operate your monitor only at a comfortable brightness / contrast level. This may help your eyestrain.
Good Luck
Jim Witkowski
Chief Hardware Engineer
Cornerstone / Monitorsdirect.com