Dry eye/strain. Dry eye or eye strain can cause discomfort. Try using artificial tears to help lubricate the eye and see if that helps. You may also want to have your vision checked to see if glasses could help.
Could be dry eyes? Sometimes when we focus on an object that we are interested in (tv, computers, video games), we don't blink as much as usual. The reduced blinking causing the eyes to have dryness and discomfort. Try artificial tears prior to watching tv and see if that helps. If not, maybe you have a mild prescription for glasses and are getting eye strain trying to focus on the tv.