Software developed/designed/engineered to interrupt the pc-user's screentime to perform some office-friendly exercises already exists. However, this software is more focused on preventing bad posture and RSI.
- Adjusting screen-settings (contrast/brightness) to a dimmer level.
- Don't stare into a bright screen while sitting in a dark room. Use light from the space where you work, aside of a desk lamp. I'm not sure whether it's supposed to brighter than the light on your screen, or whether a matte/glossy monitor is better. On the other hand, due to the active nature of using a computer compared to watching tv, working in a dark room might be better depending on preference or activity - like mmorpg versus typing a Word document versus writing code.
- A dark page with bright lettered-texts is easier on the eyes.
- There have been studies on what the eyes tend to focus on when presented with certain stimuli, which indicates a certain preference concerning lay-out and the grouping of columns.
Albeit not on-topic, in my opinion equally problematic (unconsciously) is the prolongued/ongoing exposure to (other people's/calibrating machine's) computing sounds, which can influence your mood and performance if you are hearing-sensitive.