FAQs: Understanding Refractive Error

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If you’ve ever been to an eye doctor, you’ve probably heard of the term refractive error.

Refractive errors are “optical imperfections” which prevent light from focusing directly on the retina, thus causing blurred vision. These imperfections can include length of the eyeball, changes in the shape of the cornea or aging lens.

Here are some of the most commonly asked questions (and answers) about refractive errors. Read on and be informed!

Image from the National Eye Institute
Image from the National Eye Institute

First things first, what is refraction?

According to the National Eye Institute, refraction is the “bending of light as it passes through one object to another.” Normal vision happens when light rays are refracted as they pass through the cornea and the lens. The light focuses on the retina and the retina’s job is to convert these light rays into the images that we see through the optic nerve of the brain.

Video Source: sciencelearn.org.nz

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What are the types of refractive errors?

 

  • Myopia or nearsightedness. As the name implies, people with myopia see distant objects much less clearly compared to how they see objects up close. Myopia happens when the light focuses in front of the retina instead of on the retina itself. Learn more about myopia here.
invisalens - Untreated Myopia1
Source: Invisalens
  • Hyperopia or farsightedness. Farsighted people see distant objects better than they do objects up close. In the case of hyperopia, the light focuses behind the retina instead of directly on it. Usually, the eyeball of a farsighted person is shorter than the average.
Orthokeratology vs. LASIK Surgery1
Source: Invisalens
  • Astigmatism. According to an article in the American Academy of Ophthalmology, astigmatism is a refractive error caused by an “imperfection in the curvature” of the cornea or in the shape of the eye’s lens. The cornea and the lens should normally be smooth and curved equally so light can focus sharply on the retina.
Source: AOA
Source: AOA
  • Presbyopia. Presbyopia is also known as the aging eye condition. It commonly occurs as a person ages. The hardening of the eyes’ natural lenses makes it hard for the eyes to focus light onto the retina. People with presbyopia have trouble focusing on objects up close.
Source: NEI
Source: NEI

Aside from blurred vision, what are the most common symptoms of refractive errors?

  • Seeing double or seeing glare or halos when looking at bright lights
  • Experiencing head ache, eye strain
  • Squinting
  • Having difficulty reading

 

What causes refractive errors?

When the eyes are unable to focus light properly on the retina, it means that there is a problem with at least one of these three eye anatomy features:

Invisalens - better vision
Source: Invisalens
  • Eye length. When the eyes are too long, light is focused before it reaches the retina and the effect is nearsightedness. When the eyes are too short, light is not focused when it reaches the retina and the the effect is farsightedness.
  • Curvature of the cornea. If the cornea is not “perfectly spherical,” the image from the retina is “focused irregularly” which causes astigmatism.
  • Curvature of the lens. When the lens is “too steeply curved” vis-à-vis the length of the eye and curvature of the cornea, the result is myopia. When the lens is “too flat,” the result is hyperopia.

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“Your Child May Be Losing Out on Life Because of Myopia”

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Who are at risk of refractive errors?

Refractive errors affect both children and adults. Many children today are particularly vulnerable to myopia. Presbyopia, meanwhile, affects adults especially those over the age of 35. It is not uncommon for a person to have presbyopia and another refractive error at the same time.

Invisalens-Child-2
Source: Invisalens

How are refractive errors diagnosed and treated?

When you start to experience the above-mentioned symptoms with varying levels of intensity and frequency, then it is time to consult with an eye care professional. Your eye doctor will perform a diagnostic test called refraction. It can be done either with a computerized instrument (this is called an automated refraction) or with a mechanical instrument called a phoropter (this is called a manual refraction).

Refractive errors can be corrected using prescription glasses, refractive surgery (LASIK), regular contact lenses or Vision Improvement Therapy (VIT). VIT is based on the tried and tested science of Orthokeratology or Ortho-k. This refers to the non-surgical use of tailor-fit, gas permeable overnight lenses which when worn causes the wearer to wake up to significantly improved vision.

Can refractive errors be prevented?

The World Health Organization (WHO) notes that refractive errors cannot be prevented, though we know that it can be diagnosed and corrected. Of course, it always helps to practice good eye care habits to avoid worsening current eye and vision issues.

Why is it important to know more about refractive errors?

According to the International Agency for the Prevention of Blindness (IAPB), uncorrected refractive errors are the “main cause of vision impairment.” Vision impairment can have lasting adverse consequences such as missed education and employment opportunities, lower productivity, and low self-esteem, among others. The WHO estimates that 153 million people from around the globe are visually impaired due to uncorrected refractive errors.

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