It’s been a few years—OK, let’s be honest, more than a few years—since you last had a comprehensive eye exam. But you can see fine with your current prescription. What are the odds that you really need a new exam?

Glad you asked—it’s 58%!

That’s the finding of a Canadian study of more than 2,500 people who went for a routine comprehensive eye exam. They were all “asymptomatic,” meaning that they had no preexisting condition such as an eye disease or diabetes that would require more frequent eye exams.

The last time the 40-to-64 year olds had been examined was nearly three (2.9) years earlier, on average. For those 65 and older, it was between one and one-and-a-half years earlier. Findings…

  • 41% needed new spectacle prescriptions.
  • 16% had new “critical” diagnoses, such as glaucoma or cataracts.
  • 31% needed new “management,” such as a referral to another doctor or a new treatment.

Put it all together and a full 58% of those who went in for a routine eye exam had some benefit from the visit. The older the patient, the more likely the exam turned up something, even if just a prescription change.

HOW OFTEN SHOULD YOU GO FOR AN EYE EXAM?

The American Academy of Ophthalmology recommends that “asymptomatic” men and women get a comprehensive eye exam (which includes checking for glaucoma, age-related macular degeneration and cataracts)…

  • Age 40 through 54: Every two to four years.
  • Age 55 through 64: Every one to three years.
  • Over 65: Every one to two years.

The new research suggests that it may be prudent to follow the earlier side of those ranges. If your eye doctor recommends more frequent exams based on a specific condition or your health history, follow that advice instead, of course.

We’re not talking about just getting your prescription tested by an optician—a full exam can pick up a long list of eye conditions, the earlier the better. The older you are, studies show, the more likely these exams will help not just adjust your prescription but reduce your risk for vision loss. In short, it’s an appointment that could save your sight.

Related: Find out 13 ways to get sharper vision.