Refractive Errors: Types, Signs, Causes, and Treatment

Refractive errors are disorders that affect the way your eyes bend light. They cause certain objects to appear blurry. These disorders are very common and are caused by abnormalities in the shape of the eye. You can either be born with refractive errors or develop them later in life.

An eye doctor can diagnose a refractive error in a routine eye exam. If you have this problem, there are several treatments available to correct your vision on a temporary or permanent basis.

What Are Refractive Errors?

About 670 million people do not have access to corrective treatment and are considered visually impaired.

Indian Journal of Ophthalmology

Refractive errors are eye disorders that affect the eye’s ability to refract or bend light. This makes it difficult for the eye to focus on what it is seeing. Depending on the type of refractive error, you may struggle all the time or only in specific situations.

The severity of the error determines how much it will affect your vision. Mild errors may hardly affect your sight at all, while severe errors may leave you unable to live a normal life without vision correction.

You can have a refractive error in one or both eyes. When an error is present in both eyes, it may not be equally severe in both. You can also have different refractive errors in each of your eyes.

Refractive errors are extremely common. Around 2.3 billion people globally have one or more refractive errors affecting their sight.

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What Types of Refractive Errors Exist?

There are four main types of refractive errors:

• Myopia, or nearsightedness – difficulty seeing things that are far away.
• Hyperopia, or farsightedness – difficulty seeing things up close.
• Presbyopia, an age-related form of farsightedness that sometimes happens when the lens of your eye hardens over time.
• Astigmatism, or blurred vision at all distances.

Symptoms

Some of the symptoms of refractive errors include:

• Blurry vision. You may experience this symptom when looking at things that are either far away or up close, or sometimes both.
• Double vision
•  Hazy vision
• Headaches, especially when reading or using a computer for long periods of time
• Eye strain (soreness or tiredness in your eyes)
• Seeing halos or glare around bright lights, especially at night

Risk Factors

Some people are more likely to be affected by refractive errors than others, including:

• Older people. Your risk of developing hyperopia increases each year until age 70. After 70, your risk of developing myopia increases. Older people are also more likely to develop presbyopia due to the way your lens hardens over time.
• People with close relatives who have refractive errors. These disorders tend to run in families and may have a genetic basis.

Some studies have also found a link between environmental factors and the development of late-onset myopia. These include:

• Not spending enough time outdoors
•  Use of LED lamps
•  Long periods of “near work,” meaning work that is done close to your face
•  Poor sleeping patterns

Causes

Refractive errors are caused by three different factors:

• Eyeballs that are too long or too short
• Abnormalities in the shape of the cornea
• Aging lenses

Because your eyes change and grow over the course of your life, you may be born with one of these problems or develop it later in life.

Diagnosis

Refractive errors are usually diagnosed using a simple vision test. This is the same test you receive when you get your eyes checked during a routine optometrist visit.

Everyone gets presbyopia as they get older, usually after age 45 and many people have another refractive error in addition to presbyopia.

National Eye Institute

First, your eye doctor will ask you to close one eye, then look at a chart positioned on their office wall through the special device that is installed in front of the patient chair. This device has many different lenses so the doctor can see how well you can see through them.

During the test, your doctor will ask you to read the letters on the chart while looking through several different lenses. Your answers will help them determine how your eyes refract light.

If your doctor determines your eyes do not refract light well enough to give you a normal range of vision, you will be diagnosed with a refractive error. Your eye doctor will then write you a prescription for corrective eyewear that will improve your vision.

Treatments

Refractive errors can be treated using:

• Eyeglasses. Prescription glasses are worn to correct your sight when your refractive error becomes a problem, such as when reading or driving.
• Contacts. Contacts are thin pieces of flexible plastic that are made according to your prescription, just like glasses. Many people prefer contacts to glasses because they can be worn discreetly. Some people also find contacts to be more practical during physical activity. 
• Laser eye surgery. During laser eye surgery, your surgeon reshapes the surface of your cornea, the outside part of your eyeball,  to allow it to better refract light. This offers permanent results, but it also carries a risk of complications.
• Intraocular lens surgery. During intraocular lens surgery, your surgeon will replace your eye’s natural lens with a plastic lens called an intraocular lens. This new artificial lens is perfectly shaped and will eliminate any refractive errors in your eye.

 FAQs

What are the different types of refractive errors?

There are four common types of refractive errors:

• Hyperopia, or farsightedness
• Myopia, or nearsightedness
• Presbyopia, or age-related farsightedness
• Astigmatism

What causes refractive errors?

Refractive errors are caused by small variations in the shape of your eyeball or cornea. Your eyeball may be too long or too short to focus light properly. Your cornea may also not be curved at the right angle to refract light the way a typical eye can.

What is the most common refractive error?

Astigmatism is the most common refractive error worldwide, affecting 40.2 percent of the adult population. It is also the most common refractive error in the US.

References

1. Refractive Errors. (August 2020). National Eye Institute.

2. Refractive Errors. (2021). Johns Hopkins Medicine.

3. Blindness and vision impairment: Refractive errors. (October 2013). World Health Organization (WHO).

4. Eyes – refractive errors. (2021). Better Health Channel.

5. Uncorrected refractive errors. (September 2012). Indian Journal of Ophthalmology.

6. Global and regional estimates of prevalence of refractive errors: Systematic review and meta-analysis. (March 2018). Journal of Current Ophthalmology.

7. Medical Tests: Refraction. (2021). UCSF Health.

8. Modifiable Environmental Risk Factors Affecting Myopia. (June 2021). Journal of Clinical and Experimental Ophthalmology.

9. Risk factors for eye disease and injury: literature review. (December 2008). Australian Government Department of Health.

10. Refractive Errors. (2021). University of Michigan Health: Kellogg Eye Center.