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Emmetropia & Ametropia: What Is the Difference?

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Emmetropia is a term that refers to the condition of having “normal” 20/20 vision, with eyes free of refractive errors.

Ametropia refers to the broad condition of having some form of refractive error present in your eye. Common forms of ametropia include myopia, hyperopia, and astigmatism, which can often be corrected with prescription lenses.

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emmetropia ametropia exam

What Is Emmetropia?

Emmetropia refers to a lack of refractive errors present in the eye. This state allows a person to have what is called “20/20 vision.”

The first number in this term means an individual can see at 20 feet what standard vision would allow a person to see at the second number. Hence, people with no refractive errors can generally see at 20 feet exactly what is expected with normal vision.

What Is Ametropia?

Ametropia refers to an ocular system in which there is a refractive error. The term is very broad, and it is more common to hear reference to the errors that qualify. These are common refractive errors:

  • Myopia (nearsightedness)
  • Hyperopia (farsightedness)
  • Astigmatism
  • Presbyopia

Causes of Ametropia

The term refractive error refers to the way light refracts into the retina.

In a completely healthy human eye, the eye focuses light on the retina — the part of the eye that sends visual information to your brain. Refraction errors shift that light, causing objects to look blurry or distorted.

Many things can cause ametropia, including having an elongated or shortened eyeball, a misshapen cornea, and an aged eye lens. Presbyopia, which makes seeing up close more difficult, is very common among older adults because of the natural aging process.

Differences Between Emmetropia & Ametropia

If we consider emmetropia as a “default,” where a person sees with a standard level of visual acuity, then ametropia is characterized by symptoms such as these:

  • Double vision
  • Hazy vision
  • Distracting glaring or visual artifacts
  • Halos around bright lights
  • Headaches
  • Eye strain
  • Difficulty focusing

Like many vision problems, ametropia exists on a spectrum. Some people may have such mild refractive errors that they don’t notice them unless given an eye exam.

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The board-certified surgeons at NVISION have performed over 2.5 million procedures. Your journey to better vision starts here.

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Treatment for Ametropia

Most people who have refractive errors can have their vision corrected with corrective lenses, such as contacts or glasses. These devices redirect light that passes through them, helping to focus it onto the retina and provide better visual acuity.

Many people can achieve 20/20 corrected vision, meaning their vision is at the standard level once they wear corrective lenses.

An option for some patients is LASIK, or laser-assisted in situ keratomileusis, a procedure in which a surgeon uses an extremely precise laser to reshape the cornea. If successful, this surgery can redirect how light passes through a person’s eye, improving their vision. In some cases, they may achieve 20/20 vision or at least a level of acuity where glasses become unnecessary unless doing specific tasks, such as reading or driving.

While glasses present almost no risks (with most even made of shatter-resistant material), contact lenses can introduce germs to the eye if improperly cared for. LASIK comes with standard risks related to any surgical procedure; however, overall, complication rates are extremely low.

Protecting Emmetropic Eyes

Some vision loss is inevitable with age. People may develop vision problems as a result of unavoidable injury, genetics, or complications at birth. Refractive errors themselves often aren’t truly preventable, but they also aren’t the only conditions that can impact your sight.

If you presently have emmetropic eyes, following some basic best practices may help you maintain perfect or at least good vision much longer. The CDC recommends the following:

  • Eat a diet rich in fruits and vegetables.
  • Work to avoid diabetes and practice good discipline if you have it.
  • Main a healthy weight, both to avoid diabetes and improve circulation.
  • Quit smoking. Don’t start smoking.
  • Wear sunglasses when outside.
  • Always wear safety goggles when appropriate for a given task.

Get Regular Eye Exams

One of the best ways to prevent avoidable vision loss is through regular eye exams.

Experts recommend a different timeline for exams depending on your age. If you show signs of any eye problems, your doctor may recommend a different schedule, with more frequent visits.

Most families can begin taking their children to tests once they first learn the alphabet and then every year or two until they become adults. If a child seems like they may have vision problems, take them right away, even if they haven’t learned the alphabet.

Between the ages of 20 and 39, the recommended rate of eye exams sharply decreases unless a doctor or the patient notices an issue. You can safely get an examination every 5 to 10 years, although the recommendation is yearly exams if you wear contact lenses.

As an adult ages, eye exams are recommended with more frequency.

  • For adults 40–54: Every 2–4 years
  • For adults 55–64: Every 1–3 years
  • For adults over 65: Every 1–2 years

Beyond any time or financial inconvenience, seeing a licensed doctor more frequently than the above recommendations poses no harm to a patient. If you ever have a concern your vision has changed or even want to confirm something, like the accuracy of your prescription, visit an eye doctor.

Many people see an eye doctor only when a significant problem occurs, but going at the recommended rates can help catch complications early and may help prevent vision loss.

References

  1. Emmetropia – The Perfect Imperfection. (December 2020). Indian Journal of Ophthalmology.  
  2. Influence of Ametropia and Its Correction on Measurement of Accommodation. (June 2016). Visual Psychophysics and Physiological Optics. 
  3. LASIK. (March 2018). U.S. Food and Drug Administration.
  4. More Eyes With 20/10 Distance Visual Acuity at 12 Months Versus 3 Months in a Topography-Guided Excimer Laser Trial: Possible Contributing Factors. (May 2019). Journal of Cataract and Refractive Surgery.
  5. Refractive Errors. (March 2022). National Eye Institute. 
  6. Standard Eye Exam. (March 2021). MedlinePlus. 
  7. Tips to Prevent Vision Loss. (August 2021). Centers for Disease Control and Prevention.
  8. What Is 20/20 Vision? (May 2018). University of Iowa Hospitals & Clinics

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