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Ametropia: Description, prevalence and treatment

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What is ametropia?

Ametropia is the medical term for the presence of refractive error in the eyes. It occurs when the eye is not able to focus light rays from an object directly onto the retina to provide a clear image. Ametropia includes refractive error due to myopia, hyperopia and astigmatism.

In myopia (nearsightedness), the light rays focus in front of the retina. In hyperopia (farsightedness), the light rays focus behind the retina. In astigmatism, the refractive error of the eye is different at different axis or meridians.

How does ametropia affect people’s lives around the world?

Ametropia is the most common eye problem in people of all ages around the world. 

In a 2016 study, it was found that uncorrected refractive error was responsible for visual impairment in over 100 million worldwide and blindness in nearly 7 million people. This is the equivalent of nearly one in 100 people in the world with decreased or lost vision due to ametropia.   

Uncorrected ametropia has countless negative outcomes for individuals, their families and society in general. Poverty and poor access to eye care prevent many people around the world from receiving treatment to correct their refractive error. This has a ripple effect of decreased socioeconomic status for these individuals and their families. Education and employment opportunities become limited for those who suffer from ametropia.

Thanks to increasing awareness and medical outreach, the prevalence of visual impairment and blindness due to ametropia decreased by nearly one third from 1990 to 2010.

RELATED READING: Visual impairment around the world

Are there ametropia types?

Ametropia simply means that a refractive error is present, so it isn’t quite accurate to say there are types of ametropia. But there are types of refractive error. The three most common types of refractive error are: 

Myopia

In myopia, light rays entering the eyes are focused at a point in front of the retina, resulting in a blurry image. This can be due to “too much” refractive power if the cornea is too steeply curved. More commonly, it can be due to the eye having too long an axial length. This is known as “axial myopia.”

Myopia is considered to be the most common cause of refractive error in many countries. Researchers have found that myopia prevalence increases or decreases based on several factors. 

Prevalence of myopia may increase with:

  • Less time spent outdoors

  • More time spent in near work activities

  • Age in low-economic communities

  • Higher education

Prevalence of myopia may decrease with:

  • Age in high-economic communities

  • More time spent outdoors

An alarming worldwide trend is an increased prevalence of myopia. Particularly in some East Asian countries, researchers have found that nearly four in five adults over age 18 are myopic. While not as high, the trend for increasing myopia has also occurred in the Western hemisphere. According to the American Optometric Association, myopia affects nearly one in three Americans.

Childhood myopia is especially concerning as the rise in myopia has been particularly high in school-aged children. This increase in myopia throughout the world results in lost opportunity and productivity. It can also lead to vision-threatening conditions such as retinal detachment.

Many different types of strategies have been shown to slow down the progression of myopia, including:

  • Spending more time outdoors.

  • Bifocal and progressive addition lenses.

  • Undercorrection.

  • Use of ocular accommodation-limiting drugs such as atropine.

  • Wearing myopia control glasses.

Hyperopia 

In hyperopia, light rays entering the eyes are focused at a point behind the retina, resulting in a blurry image. This can be due to “insufficient” refractive power in the cornea or lens or to the eyeball being too short (having a short axial length).

The prevalence of hyperopia in the U.S. is about one in 10 Americans.  In babies, hyperopia is the most common refractive error. This hyperopia typically decreases within a few years as the baby grows into toddlerhood.

The current trends of refractive error around the world indicate that the prevalence of hyperopia is low compared to myopia.

Astigmatism

Astigmatism is the result of the refractive error of the eye being different in the meridians of the eye. Usually, it is due to the curve of the cornea being irregular. The correction that is required to correct astigmatism is more complex than a simple spherical correction of myopia or hyperopia. 

Factors that increase your risk of astigmatism include:

  • Farsightedness or nearsightedness.

  • Black or Hispanic ethnicity.

  • Having a mother who smoked while pregnant.

What is the risk of not detecting ametropia in babies and children?

Children may not realize that their blurry vision is not normal. Since they do not have any other reference point, they may not speak up about visual difficulties due to ametropia.

If ametropia goes undetected in young children, they can be at risk for a condition called amblyopia (“lazy eye”). This condition can be treated if detected early, but it can result in life-long decreased visual acuity and depth perception if detected too late. 

It is important to look for signs such as avoidance of near work activities, squinting, short attention span and eye discomfort in children. Children may perform poorly at school or in sports due to symptoms resulting from ametropia. While vision screenings are helpful in catching refractive errors, a thorough exam with an eye doctor is necessary to detect and treat ametropia. 

What are the symptoms of ametropia?

Ametropia can make daily tasks difficult and, sometimes, dangerous. Reading, playing sports, cooking safely and driving safely all require clear vision.

Symptoms of uncorrected ametropia include:

If you notice any of these symptoms, schedule an appointment with an eye doctor.

How is ametropia treated?

Detection of refractive error usually occurs when an individual notices blurry vision. In children, it can be found by school screenings, parent observation, a child’s complaints or yearly visits to the eye doctor. 

Ametropia can be treated by:

Glasses and contact lenses have been used to treat ametropia for a long time. While refractive surgery is relatively new, it is an effective and typically safe option to correct ametropia. 

Can ametropia be prevented?

A tremendous amount of research is currently being done to determine how to prevent and slow down ametropia, especially myopia.  

Some things that you can do to decrease your risk of ametropia are:

  • Spend time outdoors.

  • Take breaks when doing near work (Try the 20-20-20 rule: every 20 minutes, for 20 seconds, look at something at least 20 feet away).

  • Decrease or limit screen time.

  • Use proper illumination, with the light pointing at your desk, not your eyes.

  • Don’t smoke.

  • Wear sunglasses and protective eyewear.

  • Ask your eye doctor about current technology in slowing progression of myopia in children.

  • Eat a healthy and nutritious diet rich in Vitamin A, C and Lutein.

There is continuing research in how to decrease or prevent the progression of ametropia. During your visit to the eye doctor for a comprehensive eye exam, ask them about the latest technologies in the treatment and management of refractive error.

Global vision impairment and blindness due to uncorrected refractive error, 1990–2010. Optometry and Vision Science. March 2016.

Prevalence of refractive error in Europe: the European eye epidemiology consortium. European Journal of Epidemiology. March 2015.

Global variations and time trends in the prevalence of childhood myopia, a systematic review and quantitative meta-analysis: implications for aetiology and early prevention. British Journal of Ophthalmology. January 2016.

Myopia (nearsightedness). American Optometric Association. Accessed October 2021.

Practical applications to modify and control the development of ametropia. Eye. December 2013.

Hyperopia. American Academy of Ophthalmology. EyeWiki. February 2020.

Astigmatism. Cleveland Clinic Foundation. December 2020.

Myopia (nearsightedness). Cleveland Clinic Foundation. July 2020.

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