It depends on the causes. If your eye strain just caused due to spending a lot of time on the computer, getting your eyes relaxed every 20 minutes, blink 10 times, or with the help of the computer eye strain glasses, it will go away soon. The actual strain can last for minutes to hours after you stop straining your eyes. If you have a persistent discomfort no matter what you do, you should have an examination by your eye doctor.