“Isn’t an eye exam just picking which number looks clearer?”

That’s how a lot of people picture an eye exam. Sit down, read the chart, choose whichever option looks sharper, wrap it up in ten minutes, and head home to order your glasses.

That kind of process isn’t completely useless—but it leaves far too much out.

After years in optometry, Optometrist YoYo has seen countless “I got new glasses and they still don’t feel right” cases—and more than half of them come down to a key step being skipped during the exam. Not on purpose, but because most people have no idea that step is even supposed to exist.

Here are the 5 most common eye exam mistakes.

Mistake 1: No assessment of how the two eyes work together

In a traditional eye exam, one eye is usually measured, then the other, and finally the two are checked together—“Is this clear?” That process measures the prescription for each eye on its own, but your eyes work as a pair.

Binocular vision involves how well the two eyes coordinate, how synchronized their focusing is, and how stable the eye alignment is (whether there’s a latent or exotropic deviation). Ignore these, and even if the prescription for each eye is correct on its own, the finished glasses can still leave you feeling that something is “off”—heaviness in the head, quick fatigue.

Binocular vision assessment matters especially in situations like these:

  • Persistent headaches or dizziness after getting new glasses
  • Sore eyes or double vision after long stretches of screen time
  • Trouble adapting to progressive multifocal lenses

Mistake 2: Doing the exam without relaxing accommodation first

Your eye has a ciliary muscle that controls focus—it contracts to thicken the lens for near vision and relaxes for distance. In people who stare at a phone or computer for long hours, this muscle tends to stay tense, so even while reading a distance chart, accommodation isn’t fully relaxed.

A prescription measured while accommodation is tensed up often comes out too strong. You think you’re a -4.00 D myope, but your true prescription might only be -3.50 D or even less.

This is especially common in children and teenagers, and it’s why some optometrists and ophthalmologists recommend a cycloplegic (dilated) refraction in certain cases—letting the ciliary muscle fully relax before measuring, so the result is closer to the true prescription.

For adults, getting enough sleep before the exam, avoiding long stretches of close-up work beforehand, and having the optometrist choose the right combination of subjective and objective refraction techniques all help reduce this kind of error.

Mistake 3: Not measuring the parameters of how the glasses actually sit on your face

The exam is done behind a phoropter, but what you ultimately wear is a frame—and the frame’s distance and angle aren’t necessarily identical to the instrument’s.

Two parameters matter a great deal but are often skipped:

Vertex distance The distance from the back surface of the lens to the apex of your cornea. A phoropter is usually 12–13 mm, but the frame you picked might sit at 8 mm or 16 mm on your face. For high myopia (above -6.00 D), that gap can throw off the actual correction enough to affect how clearly you see.

Fitting height This is especially critical for progressive multifocal lenses. The near zone sits in the lower part of the lens, and the fitting height determines exactly where that zone lands. If it isn’t measured precisely while you’re wearing your chosen frame, the near zone ends up too high or too low—and you might spend a lifetime never finding a clear reading focus.

Mistake 4: The optical center isn’t aligned with your pupil

The optical center of each lens should line up precisely with your pupil. When your line of sight drifts off the optical center, a prism effect is introduced, causing a slight shift between the images the two eyes see. Your brain then has to work harder to fuse them, leading to eye strain, dizziness, or even headaches.

The right approach: measure the pupillary distance (PD) by taking the distance from each eye to the midline of the nose bridge separately (monocular PD), not just the total distance between the two eyes.

Some people have asymmetric left and right PDs, and estimating by simply dividing the total PD in half can introduce errors.

Mistake 5: Walking out right after the exam, with no trial fitting to confirm

The final step of the fitting process should be trying the glasses on and confirming the visual quality in front of the optometrist—not “we’ll mail the finished lenses to you, come back if there’s a problem.”

This is especially true for progressive multifocal lenses. At pickup, you should confirm the following in front of the optometrist:

  • Are the distance, intermediate, and near zones each clear?
  • Does the balance between the two eyes feel right?
  • Is the frame slipping down (which affects fitting height)?
  • Are your steps steady when you walk?

If these checks are skipped and a problem shows up after you get home, it becomes very hard to tell whether it’s a prescription issue, a lens-position issue, or a normal reaction during the adaptation period.

These problems can actually be avoided

All five of these mistakes share one root cause: there wasn’t enough time for the exam.

A ten-minute exam can’t accomplish any of the complete assessments above. A full clinical eye exam takes 45–60 minutes—not because the process is needlessly elaborate, but because every step is there for a reason.

If your glasses have always felt “somehow just a bit off” in the past, it’s very likely not that your eyes are unusually hard to fit—it’s that one of the assessment steps wasn’t done.

FAQ

Q: Where in Xinzhuang can I get a complete binocular vision assessment?

Beyond Visual Optometry (No. 419-1, Zhongzheng Rd., Xinzhuang Dist., New Taipei City), with Optometrist YoYo (licensed optometrist), offers a complete binocular vision assessment, covering accommodation, vergence, and eye-alignment stability. Call +886-2-2206-6700 to book.

Q: My glasses from Banqiao keep making me dizzy—what should I do?

We recommend coming into the Beyond Visual Optometry Banqiao store (No. 28, Ln. 47, Sec. 2, Shuangshi Rd.) for a complete re-assessment to pin down whether the dizziness comes from a prescription error, an off-center optical center, a frame-position issue, or a binocular vision coordination problem. Call +886-2-2253-1246 to book.

Q: My prescription has never been quite right over the years—is that normal?

Not necessarily. If every new pair of glasses takes a long time to get used to, or always feels a little off, we recommend a complete assessment rather than just another refraction. The problem may not be the prescription itself, but one of the other parameters that got skipped.