Eyestrain is reduced by altering the reflective blue rays of the screen, reducing glare, and blocking the harmful UV light rays from the computer screen. Using computer glasses will help you to have fewer headaches.
Yes, you still need to get away from the computer and the desk every twenty minutes if possible. No? Okay then, every hour and take a walk about and stretch. Have a look at the index of stretches from Bob Anderson's book, Stretching in the Office, or available as StretchWare, software that reminds you to stretch. And have a drink of water.
Just a reminder, that it is not a treat, it is a necessity to get a massage when you are wearing your shoulders as earrings from the stress of work, worries and deadlines.