For your problem, I think there are two reasons.
Firstly, you may often rub your eyes. and your eyes are relatively big or your eyelashes are a little short or skimp so as not to protect your eyes from the entrance of sand or dust. Besides, if you spend too much time in front of computer, you will feel tired and spend more time rubbing your eyes.
We all know, outside our eyeball there is a layer of membrane, and under that there is rich of blood capillary, if you often oppress your eyeballs, there will be trace of bleeding in capillary, as time passes, more and more trace hemorrhage can't be absorbed completely and timely, which accumulated in ocular surface within the organization. then the white part of your eyes will turn yellow (or light orange, pale brown), but your eyes may not feel uncomfortable.
I suggest you wear a pair of flat glasses in sandstorm days while going out, and have a rest for 10-20 minutes after working 1-2 hours in front of computer. To protect your eyes, you can see the distance far away or green plants when your eyes feel tired. besides, pay attention to your nutrition, be sure to eat more vegetables, take some vitamins, or do some eye exercises etc. Try not to use hands to rub eyes, you can ask someone to blow off or use a clean handkerchief to wipe out the foreign matter in your eyes, or you can close your eyes and have a rest for a while. In addition, if you have some diseases with your liver, the white part of your eyes will also turn brown, I suggest you do some examine in hospital.
Wish you have a good health and charming eyes.