Fish oils contain vitamin A, which is essential for good eyesight. Lack of Vitamin A can cause 'Night Blindness', where it can be difficult to see things in dim light. However, only a very small amount is needed, and it is found in fish oil, milk and yoghurt, cheese, liver, red and orange vegetables, and some dark green vegetables. A sensible western diet will be providing all you need.
If you need glasses to properly view the computer screen, the EU states that an employer must provide for a free eye test, and meet the cost of any basic spectacles you may need. You are also entitled to a break from watching the screen, and this should be at least once an hour. So get up, move around, and do something else.