You sit down to lunch at your favorite diner. Curious about the daily specials, you reach into your pocket for your eyeglasses and come up empty. No big deal—your wife’s specs always do in a pinch, right?

Yes and no, says Julie Schaefer, O.D., a Miami–based optometrist with South Florida Regional Eye Associates, located inside an America’s Best Contacts & Eyeglasses.

“I often see spouses borrowing each other’s reading glasses to look at a menu, and that’s OK in the short term,” says Dr. Schaefer. “But if you’re using someone else’s prescription eyeglasses to drive or to work at a computer, that’s definitely not a good idea.”

You won’t damage your eyes, she says, but you will overtask them. Plus, if borrowing is becoming a habit, it’s a sign you’re due for an eye exam. (Find an America’s Best location near you.)

You’re not alone: Nearly two-thirds of Americans say they don’t see as well as they’d like to, but just one in eight have had a recent eye exam, according to a 2016 national survey conducted by the American Academy of Ophthalmology.

Count yourself among this group? Check out Dr. Schaefer’s top reasons to break the borrowing habit and get your eyes checked. 

Eye Doctor's Reason No. 1: It’s a Recipe for Eye Strain

Snatching glances through the wrong prescription lenses—even an outdated pair of your own—can strain your eyes. Lenses that are the wrong strength can make your eyes work harder than they should.

When it’s time to focus on a page or gauge distances between cars, your eyes pull together to share the optical load, Dr. Schaefer explains. And that’s not easy when you put someone else’s lenses in front of them.

There’s always going to be something slightly off about what you’re trying to see through eyeglasses that don’t match your prescription. As your eyes struggle to adjust, what follows is an annoying assortment of woes— headaches, sore eyes, difficulty focusing, and even a dizzy feeling.

Eye Doctor's Reason No. 2: You Deserve a Custom View

Have you ever met two people who are the same height and weight but can’t share each other’s clothes because the fit is close but not quite right? 

That’s what it’s like trying to pull off wearing your partner’s specs. There is no one-size-fits-all option.

Many people need a slightly different prescription for each eye, says Dr. Schaefer. Or they have some degree of astigmatism—a common condition, caused by irregularities in your eye’s unique anatomy, that prevents light rays from focusing properly, resulting in blurry vision.

“The biggest benefit I hear from adult patients after getting their first pair of prescription eyeglasses is how much better they see and how much it helps to relieve their eye strain,” she says.

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Eye Doctor's Reason No. 3: Your Long-Term Vision Is on the Line

“People borrow glasses for the sake of convenience,” says Dr. Schaefer. “No one actually likes making time for eye doctor appointments.”

But in your effort to keep your to-do list short, you might be missing signs of conditions that can lead to vision loss and blindness, such as glaucoma, age-related macular degeneration, and diabetic retinopathy.

Consider this: In a recent study published in the journal Optometry and Vision Science, researchers found that eye exams turned up vision problems, new eye conditions, or other significant eye-related issues in 58 percent of study volunteers who had no eye complaints.

“A comprehensive eye exam is much more than just a vision check,” says Dr. Schaefer. “We’re also screening for diseases and ensuring that your eyes are functioning properly.”

Finding eye problems early—often before you notice them—means you can begin treatments that preserve your eyesight.