A Closer Look: Refractive Errors

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A Closer Look: Refractive Errors

What are refractive errors?

A refractive error is an eye condition that can cause blurred vision, double or hazy vision, glare, headaches, and eyestrain. There are four common types:

  • nearsightedness (myopia: poor distance vision)
  • farsightedness (hyperopia: poor up-close vision)
  • astigmatism (poor up-close and distance vision)
  • presbyopia (age-related poor up-close vision)

Refractive errors are often diagnosed during a comprehensive eye examination (with dilation) and can be effectively corrected with prescription eyeglasses, contact lenses, or surgery. The risk of myopia, hyperopia, or astigmatism increases if you have a family history of these eye conditions. A refractive error can also increase your risk of developing other eye conditions, such as amblyopia (lazy eye), strabismus (crossed eyes), and more serious eye conditions, such as glaucoma, cataracts, and more. Therefore, early diagnosis and correction of any eye condition is vital to protect your sight. Without proper treatment, more serious eye conditions can lead to vision loss and blindness.

What causes refractive errors?

Refractive errors are caused when the shape of your eye (too long, too short, or football-shaped) interrupts the proper focusing of light onto your retina. Irregularities of the cornea (the transparent front covering of the eye) or the lens (the focusing part of the eye located behind the iris) can also cause a refractive error. Except for presbyopia, which occurs in middle age, refractive errors begin in childhood and continue into the early 20s. Watch this brief American Academy of Ophthalmology video to see how refractive errors affect vision.

How common are refractive errors?

Refractive errors are the most common eye condition nationally and worldwide. According to the National Institutes of Health (NIH), refractive errors impact more than 150 million people in the US alone. Correction with glasses or cataracts and, where needed, refractive surgery are used to address refractive errors. Learn more about refractive surgery from the American Academy of Ophthalmology.

Types of refractive errors

The most common types of refractive errors include:

Myopia (nearsightedness)

Nearsightedness distorts distance vision when the eye is elongated, causing light to be focused in front of the retina, not directly on it. The American Academy of Ophthalmology reports an increase in myopia in the US. This coincides with the World Health Organization indicating that 2.6 billion people were nearsighted in 2020, which is projected to increase to 3.4 billion people by 2030. A recent study suggests that almost one-third of children are affected by myopia. Based on research linking myopia to exposure to sunlight, the World Health Organization (WHO) recommends spending at least 90 minutes outdoors during daylight hours, taking frequent breaks from reading, studying, or close work, and wearing corrective lenses as prescribed to reduce the risk and severity of myopia in children.

Nearsightedness often begins between ages 6 and 14 (though some people are born with it) and progresses into the early 20s. Severe myopia, called high myopia, can lead to serious eye diseases, including glaucoma, cataracts, retinal tears/detached retina, and myopic macular degeneration. If untreated, these severe eye conditions can lead to blindness.

A comprehensive eye examination is the best way to diagnose myopia, other refractive errors, and all other eye conditions. Also, ask your eye doctor about any lifestyle adjustments, such as:

  • Eye exercises
  • Daily exposure to natural outdoor light
  • Limited screen time
  • Healthy diet and supplements

Astigmatism

According to the American Academy of Ophthalmology, thirty-three percent of people in the US have astigmatism. Although astigmatism is congenital (occurs at birth) in many cases, it can develop later in life. Both near and far vision is affected when the eye is tapered on both ends—like an American football— rather than round, like a soccer ball. Astigmatism can also be caused by injury, surgery, or keratoconus, an eye disease that causes the cornea to bulge and distort vision. Astigmatism often occurs concurrent with myopia or hyperopia and, like all refractive errors, can frequently be treated with prescription lenses or other interventions.

Hyperopia (farsightedness)

The blurry up-close vision of hyperopia occurs when the eye is too short—or a misshapen cornea or lens—causing light to focus behind the retina rather than on it. The NIH projects that 21% of preschoolers are farsighted. Although the condition is often congenital, the condition may remain undiagnosed until a child receives a comprehensive eye examination. Children with severe or untreated farsightedness may be at higher risk for strabismus (crossed eyes) or amblyopia (lazy eye). Early diagnosis and treatment are key to correcting vision and reducing the risk of additional eye diseases. Access the American Academy for Ophthalmology eye screening and eye exam recommendations for children.

Presbyopia (age-related farsightedness)

Presbyopia is a common age-related eye condition that causes blurry close-up vision. This condition often presents in the early-mid 40s and can worsen with age. While some people self-diagnose and seek to correct presbyopia with non-prescription “readers,” a comprehensive eye examination should be the first response to any change in vision.  Learn more about Common Age-Related Eye Diseases: What to Know and What You Can Do.

What about uncorrected refractive errors?

Untreated refractive errors are among the most common causes of vision loss in children in the US and globally. Failure to diagnose and treat refractive errors early can lead to amblyopia (lazy eye) and permanent blurred vision. The American Association for Pediatric Ophthalmology and Strabismus(AAPOS) stresses the importance of regular early eye examinations for children and explains more about the different types of amblyopia here.

The Big Data Project from VisionServe Alliance and The Ohio State University College of Optometry, reports that nearly 8.7 million, or 4.7% of adults aged 18 to 64, and 7.3% of adults 65+ report blindness and low vision. According to the CDC, 6.8% of children under 18 have a diagnosed eye and vision condition, with approximately 3% of children (18 or under) living with blindness or vision impairment.

Refractive errors are common and treatable with corrective lenses or other medical interventions. However, as with many eye conditions, if left untreated, some refractive errors can lead to more serious problems, including significant vision loss and blindness. Regular eye examinations, early diagnosis, and treatment are essential to maintaining eye health and preventing vision loss at any age.