It's recommended that you have an eye exam and go to the eye doctor for an eye exam at least once every year or you can go as long as every 3 years between seeing the eye doctor.
I go to my eye doctor every year once per year just to have my eyes checked and so that they can catch any possible eye problems sooner.
My eyes always turn out to be in good condition and my eyesight is good as well but it's still worth the trip and cost to see the eye doctor for a quick eye exam at least once every year.
However you can wait as long as 3 or even 5 years between eye exams if you want too.