Will using computers harm the eyes?
Computers can be a strong stimulus to practice strain, but it's not inevitable. The key to choice in avoiding the strain is to understand that it is not the computer that does anything to you, but it is in what you do to yourself in response to working on the computer.
The first issue is understanding the nature of the visual process when looking at a screen. The screen itself contains information that is occupying the mind, and it becomes possible to be so occupied that the vision is forgotten. The eyes become used and over-used, merely as transmitters of information, glued to a screen and presenting the mind with words and graphics for it to interpret. The pure process of simply seeing for the joy of it is largely forgotten, and with the fixed distance of the screen the eyes are left with precious little of what they expect: colour, movement, variety and depth - so it's no wonder they start feeling pretty neglected.
Establish habits where you take frequent breaks: looking around the room only momentarily can produce instant relief. Make your work environment beautiful to look at: plants, bright colours, pictures. Even toys and objects of curiosity dotted around the desk can provide a much needed alternative focus for the eyes to play with. Try to situate your desk so you can easily look out of a window.
If you can touch type, practise it so you can happily type with your eyes closed, or looking elsewhere. If you can't touch type, it is a skill well worth learning.
By learning to keep the eyes relaxed while working, many problems can be avoided.