Eye Refraction Tests: Purpose and Procedure

Eye doctors use eye refraction tests to check for the quality of your vision, specifically whether you have 20/20 vision. They conduct one or more of the tests as part of routine or annual eye exams. Among the exams is one that allows the doctor to diagnose your current visual acuity, allowing for a new prescription for eyeglasses or contact lenses.

What Is an Eye Refraction Test?

An eye refraction test is an exam eye doctors use to determine the ideal correction of a refractive error — an optical abnormality in which light does not focus properly on your retina. Results can help diagnose several eye conditions, but the initial benefit is that doctors can read the measurements to determine the exact prescription for your eyeglasses or contact lenses. 

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What Does 20/20 Vision Mean in Terms of Refractive Errors?

Overall, 20/20 vision is regarded as “normal or optimal vision.” The fraction refers to a specific letter size on the Snellen chart that normal healthy eyes should see at 20 feet. 

While the two numbers pertain to visual acuity, they also relate to corrective errors, specifically nearsightedness and farsightedness that someone may have. The lack of 20/20 vision is an indication of a refractive error. 

Eye Refraction Testing

The most common tests for eye refraction are:

• Phoropter refraction
• Retinoscopy
• Autorefraction

Phoropter Refraction

The most commonly used method to measure refraction involves a manual or automatic phoropter. A phoropter is a device that resembles a large mask with combinations of lenses where you look through. 

For this subjective test, you sit in front of the phoropter with a letter chart placed about 20 feet in front of you. You will read off letters from the smallest row of those visible to you. Your eye doctor will switch the lenses on the phoropter, asking which is clearer each time.

Retinoscopy

Retinoscopy is the primary test that eye doctors conduct to determine refractive errors. It is an objective test since your doctor can obtain information without your feedback.

The doctor uses a handheld device (retinoscope) to shine light through your pupil during the test. The doctor then moves the light horizontally and vertically across both eyes and observes how the light reflects off your retina. The light’s reflection patterns can be used to determine if you have a refractive error.

Autorefraction

Your eye doctor can also use an autorefractor to measure refraction. An autorefractor is a computer-controlled tabletop device that provides an objective measurement of your refractive error.

The device shines light into your eye and measures changes as it reflects off your retina. An autorefractor uses several measurements to determine when your eye is focused properly. Autorefraction provides a starting point for eye doctors in subjective refraction tests. 

Types of Refractive Errors

Results from a refractive eye test can be used to diagnose the following refractive errors:

• Myopia (nearsightedness): An eye disorder where light is focused in front, instead of on, your retina. Close objects appear normal, while distant objects appear blurry. Myopia may result from your cornea having too much curvature or your eyeball being too long.
• Hyperopia (farsightedness): An eye condition where you see distant objects clearly, but close objects appear blurry. Incoming light is focused behind, instead of on, your retina because to insufficient lens accommodation.
• Astigmatism: An imperfection in the curvature of your cornea or lens. This eye condition causes distorted double or blurry vision at any distance.
• Presbyopia: A progressively worsening inability to focus on close objects clearly. Presbyopia is the result of insufficient lens accommodation because of aging.

Who Should Be Tested?

Health care professionals recommend that everyone should undergo a refraction test alongside other eye tests regularly. This can help diagnose and treat eye conditions, many of which are asymptomatic. You should get regular refractive eye tests if you:

• Have vision problems
• Wear prescription eyeglasses/contact lenses
• Are 60 years old or older
• Have diabetes
• Have a family history of refractive errors

How Often Should You Get an Eye Refraction Test?

Several factors, including your health, age, and risk of developing eye problems, determine how often you need to get an eye refraction test. If you are healthy and under 60 years old, it is recommended that you undergo a refraction test every two to four years. 

Children should get eye refraction tests every one or two years. If you are over 60 or have a family history of refractive errors, you should have a refraction test every year. If you wear prescription eyeglasses or contact lenses, you should get a refraction test every one or two years.

Where to Get a Refractive Eye Exam

Ophthalmologists, optometrists, or orthoptists perform eye examinations, including refractive eye tests. You can schedule an appointment with any of these eye care professionals near you. The eye refraction test is conducted as part of a routine eye examination in the doctor’s office.

Costs

The cost of an eye examination, which includes an eye refraction test, ranges between $50 and $250. The national average is about $100. The cost is determined by your vision insurance (or lack thereof), the professional who performs the exam and location. If you have vision insurance, your plan will cover part of the eye exam costs.

FAQs

What is a refraction test for eyes?

An eye refraction is an examination your eye doctor performs to diagnose refractive errors and determine eyeglass prescriptions.

How does a refraction test work?

A refraction test involves various instruments and techniques that help your optometrist assess how light refracts (bends) as it passes through your cornea and lens. The doctor uses the results to diagnose refractive errors and prescribe eyeglasses.

Are eyes dilated for refraction?

In some refractive tests, such as a retinoscopy, your eyes may be dilated before the doctor performs the procedure. Dilation allows the optometrist to see your eye structures clearly for a better diagnosis. Your eye health, age and reason for exam determine if dilatation is necessary.

References

1. Comprehensive eye examination: what does it mean? (December 2019). International Center for Eye Health.

2. Visual Acuity (December 2021). StatPearls.

3. Refractive Errors (March 2022). National Eye Institute.

4. A new low-cost, compact auto-phoropter for refractive assessment in developing countries (October 2017). National Center for Biotechnology Information.

5. Sharpen your Subjective Refraction Technique. (January 2016). Review of Optometry.

6. Determination of the Refractive Correction. (2007). Clinical Procedure in Primary Eye Care (Third Edition).

7. Value of Routine Eye Examinations in Asymptomatic Patients. (July 2016). National Center for Biotechnology Information.

8. The need for routine eye examinations. (August 2004). National Center for Biotechnology Information.

9. How Often Should I Have an Eye Exam? (n.d). Prevent Blindness Organization.

10. How Much Does an Eye Exam Cost? (n.d). Cost Helper.

11. Get Free of Low-Cost Eye Care. (April 2022). National Eye Institute.

12. Is It Necessary to Have Your Eyes Dilated During Every Eye Exam? (March 2014). The University of Utah.