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What is emmetropia?

illustration of emmetropia

Emmetropia ("em-eh-TROE-pee-ah") is the medical term for naturally occurring clear vision. In other words, a person with emmetropia does not have any refractive errors — such as爱游戏ayx官网 ,farsightedness (hyperopia)orastigmatism. Someone with emmetropia has clear vision at all distances without corrective lenses and without squinting or straining their eyes.

When light enters an emmetropic eye, an image focuses perfectlyontheretina. This is unlike nearsightedness, in which light focuses images in front of the retina, or farsightedness, in which light focuses images behind the retina.

In cases of hyperopia, the eyeball is a little too short from front to back; in myopia, theeyeball is slightly too long. Emmetropic eyes are just the right length to allow light to reach the ideal spot on the retina to create crisp, clear vision.

A person with two emmetropic eyes is considered to have “ideal vision” and does not require any sort of vision correction. Emmetropia is often given as the medical definition for20/20 vision.

What causes emmetropia?

正视眼发生在有完美的平衡tween the length and the optical power of the eye. Not much is known about why some people’s eyes develop with this ideal balance while others’ eyes develop a bit long or short. Scientists believe it may involve many factors ranging from genetics to visual input in the environment.

Does emmetropia require treatment?

Because emmetropic eyes naturally produce 20/20 vision, no corrective treatment is needed to aid in visual clarity. However, people who have emmetropia can still develop other eye conditions that should receive proper attention and treatment.

Emmetropia vs. ametropia (refractive errors)

Emmetropia is the absence ofrefractive errorsin the eye. Ametropia is the opposite — it means the eyes have refractive errors. Ametropia is an umbrella term that includes the four main types of refractive errors:

Hyperopia (farsightedness)– Distant objects appear clear, but nearby objects appear blurry. This condition can be hereditary and is treated with corrective lenses such aseyeglassesor爱游戏体育.

Myopia (nearsightedness)– Nearby objects appear clear, but objects that are far away appear blurry. Like hyperopia, myopia can be hereditary and is corrected with eyeglasses or contacts. Myopia often occurs in childhood but can be developed in adulthood as well.

Astigmatism– Both near and distant objects appear blurry becausethecorneais irregularly curved. Astigmatism often accompanies myopia or hyperopia. Treatment for astigmatism includes eyeglasses or contacts.

Hyperopia, myopia and astigmatism can also be treated withrefractive surgeryif it is recommended by an eye doctor.

Presbyopia

Presbyopia与年龄相关的远视,是自然的一部分of the aging process of the eye’s lens. It usually begins around age 40, when the lens starts to lose some flexibility, and it affects everyone.

Presbyopia is considered a refractive error. However, it is not related to the length of the eye or the shape of the cornea or lens, like other types of ametropia. This means that even people who have always had emmetropic vision can develop presbyopia.

Presbyopia can be treated withreading glasses, which are available over the counter.

Protecting emmetropic eyes

Emmetropic eyes do not require corrective lenses, but that doesn’t make them any less susceptible to conditions unrelated tovisual acuity. The best way to promote healthy vision is through proper care and preventative measures, from basic eye protection to routineeye exams.

UV protection

UV rayscan be harmful to the eyes, regardless of vision clarity. In fact, too much exposure to sunlight can increase your risk of sunburned eyes,cataracts,snow blindness,eye cancerandgrowthsin or near the eye.

Be sure to protect your eyes from the brightness of the sun with 100% UV or UV400 protection in your sunglasses.

Additional eye protection

If you work outdoors or participate in sports or other activities that could potentially harm your eyes, it is important to know what kind ofprotective eyewearyou need. Sports glasses or safety goggles, in addition to UV protection, are key in preventing eye injuries that could complicate vision.

Blue light glassesare also recommended for those who spend a great deal of time looking at computers, as the blue light given off by digital screens can cause vision problems such as blurriness,爱游戏ayx网址 and more.

Routine eye exams

Regardless of the natural sharpness of your vision, certain conditions can develop with age or due to your family’s medical history.

Annualcomprehensive eye examsare the best way to detect any abnormalities or changes in vision. The earlier a problem is detected, the sooner it can be corrected. If you have any concerns with your vision, do not hesitate to contact your eye doctor.

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Definitions of myopia and other related terms. Myopia: Prevention and Control. Accessed March 2021.

Presbyopia: Everything you need to know. American Refractive Surgery Council. July 2016.

The sun, UV light and your eyes. American Academy of Ophthalmology. June 2020.

Safety glasses and protective eyewear. American Academy of Ophthalmology. March 2019.

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