There are many yoga positions that can be performed at work without any special tools or space. Many can be done at your desk.
Stretch your frame as straight as you can, press down through your sitting bones, and lift your chest. Roll your shoulders back a few times letting them pull and then relax. Inhale deeply through your whole body, and then exhale in the same fashion. Allow the breath to leave you at it’s own pace, let your body relax around the exhalation and stretch up slowly, swelling with the inhalation. Perform this exercise multiple times while you feel your body relax.
Your eyes are easy to overwork in an office environment and eye exercises can help to ease the stress and strain they are subjected to. Lift your eyes from your work or your computer screen and focus on a spot on a nearby wall. Imagine a circle on the wall and follow the line around its circumference, slowly circling, first in one direction, then in the other. Then focus your gaze further away and practice the same exercise. Then focus your eyes back onto something near (but not your computer screen). Repeat this process a few times.
Wrists are subject to repetitious work that can cause problems with the tendons and other parts of the wrist. To reduce the chance of this, do some wrist exercises many times a day. With pinkies facing towards one another, flat on your desk, keep your fingers as straight as you can. Sit back slowly, bringing your wrists closer to your chair. As you stretch your fingertips and wrist, inhale, then exhale as you release the stretch, letting out an audible soft sigh.