Hi there--
Using any device for long, extended durations will increase your risk of eye strain, tension headaches muscle strain to the shoulders, elbows/wrists. This is has been clinically documented within the Medical Community for some time. However, these types of symptoms and musculoskeletal condition can occur with the use of any piece of equipment while maintaining a prolonged static positioning (sitting for 4 hours...)
It is always recommended to take breaks often from long term sitting, etc to avoid these potential overuse injuries.