It’s 2:30 and your head is already starting to hurt. Maybe you just need a little more caffeine, or maybe a screen break, but these headaches just seem to keep coming lately. If you’ve noticed the longer you’re at your desk the more your headache grows, it might actually be a sign you need glasses. Aside from a pounding head every afternoon, what other vision-related flags signal that it’s time for glasses (or an update to your current lens prescription)?

First things first: you need to be going to your annual eye exam, says Dr. Emilie K. Seitz, O.D., FAAO, an optometrist at Clear Eyes + Aesthetics in Cincinnati, Ohio. “Even if you feel like you can see well, we should also check the health of the eye and assess things in detail,” she says. Of course, if you notice any of these telltale signs in between your regular checkups, you should probably go ahead and book an appointment.

1. You feel like you have a hard time driving at night.

If you’re driving home in the dark, do oncoming headlights and streetlights have starbursts or halos around them? If you catch yourself squinting or having difficulty making out the details around you, it could mean you need glasses. Struggling with driving in the dark can be an early sign of your faraway vision weakening.

2. You hold things farther away to see them clearly.

Do you catch yourself holding the restaurant menu at an arm’s length to read it when you’re out to eat? Or go-go-gadget extending your phone away from you in order to read your oversharing Facebook friend’s status? That could be a sign that your vision close-up is getting worse, says Dr. Seitz. This can happen any time in life, but is a common vision change as we age.

“People in their 40s go through presbyopia — essentially, the lens inside the eye, kind of the focusing mechanism, starts to lose its flexibility. You bring things out farther to see them clearer, or you might be making text on your devices larger. This usually starts with tiny print, like on medicine bottles or the mail, or when you’re doing something like trying to remove a splinter,” she explains.

3. You frequently get headaches by the afternoon.

If your job requires a lot of computer time, be mindful that any tiredness or strain throughout the day is a sign that you might need glasses.

“We all do a lot of computer work,” says Dr Seitz. “Headaches, especially at the front, as the day goes on or when working on your tasks for an extended period signals to me, ‘Do we need to have a pair of glasses that relaxes the eyes for that distance?’”

4. You catch yourself squinting, straining, or needing to rest your eyes.

Whether you have a desk job or not, if you find yourself constantly struggling to see clearly, you probably need glasses. Dr. Seitz says you can try the 20-20-20 rule between now and your appointment to help soothe tired eyes. For every 20 minutes you spend looking at a screen, pause and look at something 20 feet away for 20 seconds. That refocusing can help your eyes relax for a moment before zooming back in on the task at hand.

Often, people tend to blame blue light from screens for eye strain, but Dr. Seitz cautions against blaming it all on that. There’s proof that blue light can mess with your sleep, but not much that suggests it causes eye strain or fatigue. “Most of the studies we have don’t really support that blue light glasses alone decrease sensitivity. Most of the time it’s just that you need a low prescription for computer work. Blue light can impact circadian rhythm, so if you’re on screens late at night, maybe consider having a dimmer on them or using nighttime mode to help. Or we can build blue light protection into the prescription lenses [for that purpose].”

How to tell if you need a new prescription

From age 20 through your early 40s, your glasses or contacts prescription should stay about the same, says Dr. Seitz. There may be “some small tweaks and changes, but if anything feels like it’s changing, just contact your doctor.” If your vision suddenly begins fluctuating — like sometimes things are clear, suddenly blurry, and then clear again — it might actually be a dry eye condition rather than a change in your vision. That’s why checking in with your eye doc is important; they can tell you what’s happening for certain.

And for what it’s worth, eye doctors prefer you get your glasses from their offices for a reason (no, not just because they want your money).

“The way different lenses are made can affect the eye, which is why we advise patients not to buy glasses online,” Dr. Seitz says. “They might be using materials that aren’t as harmonious with the eye. If you feel like you’re having changes, just come in and talk to us.”