Understanding Eye Refraction: What It Is and When You Need It | NVISION (2023)

Table of contents

  • What is eye refraction?
  • The exam
  • What can a test find?
  • Who Should Have Tests?
  • perform tests

The refraction of the eye is used to calculate the power of glasses or contact lenses. This measurement is based on how much the lens of the eye must bend light rays to process visual stimuli. This translates into a measure of distance and clarity.

According to this, more than 150 million people in the USA have ametropiadas National Eye Institute. If you have this defect, your eye cannot focus images clearly on the retina. This causes objects that are too far or too close to appear blurry.

Refractive tests can also detect other eye problems as well as the likelihood that people will need vision correction. Everyone should have a refractive test.

People nearly 60 years of age or older should be tested every year, while younger ones can be tested every two years. Vision tests like this are widely available in private practices and are generally covered by vision insurance. It may also be available through government-funded programs for low-income residents, as well as non-profit and charitable organizations.

Understanding Eye Refraction: What It Is and When You Need It | NVISION (1)

What is eye refraction?

Eye refraction is the measure of a person's required visionglassesorcontact lenses. This is calculated by a refractive test (also called an eye test), which is typically performed as part of a standard eye exam. A refractive test gives a doctor the exact measure of a prescription a patient needs for their glasses or contact lenses.

Die American Optometric Associationexplains that perfect vision is often expressed as 20/20 vision, meaning a person 20 feet away can see clearly what they should normally see at 20 feet. On the other hand, 20/100 vision means that a person would have to be 20 feet away to see what a person with "normal" vision can see at 100 feet.

These measurements are calculated by refractive tests.

20/20 Vision

People who don't have 20/20 vision have a refractive error, which means light rays don't bend the way they should when they pass through the eye's lens. This leads to distortions in the perception of visual stimuli. According toNational Eye Institute, this is the most common type of vision problem, affecting over 150 million people in America. It explains why so many people need glasses, contact lenses or other forms of vision correction.

An eye test measures the amount of bending and provides the doctor with the information needed to prescribe appropriate lenses for the patient.

What happens during a refractive eye exam?

During a refractive error test exam, your optometrist or eye doctor may perform several tests to determine the type of error you have. Doctors prefer one or both of two standard tests -- the visual acuity test and the retinoscopy exam.

visual acuity

visual acuitymeasures how well each eye can see and focus. This test requires the patient to read letters on a chart placed 20 feet away, starting with the top row and with one eye closed at a time.

The rows (letters) get smaller on the chart and the last one you can read clearly indicates your visual acuity.

A positive diagnosis of ametropia is confirmed when you cannot see the letters or symbols in line 20/20, indicating normal vision.


Retinoscopy uses a handheld instrument called a retinoscope to narrow down the diagnosis of farsightedness, nearsightedness, or astigmatism. Before beginning this procedure, your optometrist may dilate your eyes to improve the accuracy of the test.

Moving the retinoscope light horizontally and vertically across each eye, the specialist observes reflection patterns from the retina. This test allows them to determine your exact type of ametropia.

Your optometrist may ask you to view an object or chart through a phoropter to pinpoint the exact vision correction each eye needs. This device changes multiple lenses of different powers in front of your eyes.

Test results are usually evaluated within minutes to determine the best treatment plan to correct your vision. You can discuss possible corrective measures such as glasses or contact lenses with your optician.

What can a test find?

Understanding Eye Refraction: What It Is and When You Need It | NVISION (2)

An eye refraction test not only tells a doctor if a patient needs corrective lenses (and what power the lenses need to be), it also tells a doctor if the patient has a number of medical conditions, such as:

  • Astigmatism (a refraction problem based on the shape of the eye's lens that can cause blurred vision).
  • farsightedness (farsightedness).
  • myopia (myopia).
  • Presbyopia (inability of the lens of the eye to focus, associated with age-related changes in the structure of the eye).

In addition, the results of the test can help diagnose:

  • Retinal vascular occlusion (a condition that blocks the small blood vessels near the retina).
  • macular degeneration(an age-related condition that affects central vision).
  • Retinal detachment (when the retina separates from the rest of the eye).
  • Retinitis pigmentosa (a genetic disease that causes damage to the retina).

Who Should Have Tests?

Refractive tests should be performed regularly. People under the age of 60 who are healthy and do not have prominent vision problems should have a test every two years. When a child turns 3 years old, they should have a refractive test every year or two.

A person who wears corrective lenses (glasses or contact lenses) should have an eye test every one to two years. Eyes change, and regular testing helps a doctor know if a new prescription is needed, rather than a patient using corrective lenses that no longer provide adequate vision improvement. A patient who has vision problems between tests should schedule another test instead of waiting for the next scheduled test.

Where can I get a refractive eye exam?

Seek a refractive eye test if you have trouble seeing objects at a distance or up close, such as B. Text in a book. You can visit your optometrist for a proper diagnosis and a prescription for glasses or contact lenses.

An ophthalmologist's office should also have the diagnostic equipment for myopia, hyperopia, farsightedness and other refractive errors. You can see them or bring your child to them for a full eye exam or an individual test.

Most local eye doctors can help you. If that's not possible, they can probably refer you to a colleague who can.

Elderly patients and diabetics

A patient who hasDiabetesshould have an eye test every year. Diabetes is associated with a number of eye diseases such as glaucoma and diabetic retinopathy.

Understanding Eye Refraction: What It Is and When You Need It | NVISION (3)

Glaucomais a condition that occurs when too much pressure builds up in the eye, causing damage to the optic nerve and retina. theAmerican Diabetes Associationwarns that people with diabetes have a higher risk of blindness than people in the general population, making regular testing essential for this group.

People over the age of 60 or people with a family history of glaucoma and other eye disorders should have an annual refractive test. Regular examinations alert a doctor to the pressure build-up in the eye so that treatment can be initiated early.

Refraction & Eye Chart

Because refraction is a measure of how light rays bend as they enter the lens of the eye, a refractive test examines the degree to which light bends as it travels through the cornea and lens. Some doctors simply shine a light into the patient's eyes to see how much light is reflected off the retina. Based on this observation, they then calculate the refraction value. Others may use a computer to do the calculations.

This score is used by the doctor to determine the exact prescription required. This is done by placing the patient in front of a machine called aRefractor or phoropter. A refractor looks like a large mask with dozens of lenses that fits over the patient's head. About 20 feet in front of the patient is the famous letter chart (officially known as the Snellen eye chart, first developed in 1862) with different sizes on each line.

The doctor tests one eye at a time and asks the patient to read the smallest set of letters they can make out and swaps out the lenses on the refractor to find the best fit for the patient. If one eye is tested, the process is repeated on the other eye. This process gives the doctor the information necessary to prescribe lenses that give the patient 20/20 vision.

pay for refractive tests

Everyone should have a refractive test, even if they have otherwise healthy eyes. As a person ages, theStructureand the function of their eyes changes. Regular eye tests help them prepare for the gradual loss of vision that comes with age.

refractive testalso alerts doctors to the presence or development of changes in the eyes that are the result of certain diseases or conditions. Various eye diseases may not show any obvious symptoms in the person until they have caused significant damage. Doctors can detect early signs of these conditions with standard eye exams, leading to much earlier diagnosis and prompt treatment that can maximize vision preservation.

Refractive tests are a routine part of an ophthalmologist's visit and do not require patient preparation. A test can be as little as $50. Even where testing is more expensive, a biennial checkup can save significant money on future vision correction expenses.

Understanding Eye Refraction: What It Is and When You Need It | NVISION (4)

NerdWallet also points out that most refractive tests are usually covered by vision insurance, which is different from health insurance. Most health insurance companies cover vision-based medical care if the problems are identified during a refractive test. For example, the treatment of cataracts, age-related macular degeneration and glaucoma are covered by most common health insurance companies.

It is possible for all or a portion of a patient's eye exams to be covered by a standard vision insurance plan. Contact your eye insurance provider to confirm the details of your specific plan.

In addition, many state governments, nonprofits, and charities provide opportunities for low-income residents to receive free eye care that includes basic refractive testing.


  1. Visual Acuity: What is 20/20 Vision?American Optometric Association.
  2. refractive errors. (July 2019). National Eye Institute.
  3. Medical definition of refractive test. MedicineNet.
  4. Do you need a refraction during your eye exam?(November 2015). Angies Liste.
  5. Eye exams for people with diabetes. American Diabetes Association.
  6. eye complications. American Diabetes Association.
  7. What is a phoropter?(September 2018). WebMD.
  8. Snellen eye diagram for testing eyesight. (January 2020). Very good health.
  9. Common age-related eye problems. (March 2015). Cleveland Clinic.
  10. Glasses for the needy. Catholic Charities in Southwest Kansas.
  11. Optician or ophthalmologist: what is the best for your eye care?(June 2017). Cleveland Clinic.
  12. Keep an eye on your eyesight. (July 2018). Centers for Disease Control and Prevention.
  13. Recognizing myopia in the eye clinic. Community Eye Health. Access date: July 28, 2021.
  14. Myopia (short-sightedness). American Optometric Association. Access date: July 28, 2021.

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