What Is Refraction?

Reviewed on 2/18/2021
In medicine, refraction is the bending of light rays that takes place in the eye.
In medicine, refraction is the bending of light rays that takes place in the eye.

A refraction test, also known as a vision test, is an eye examination that is performed to determine a person's prescription for eyeglasses or contact lenses. It is commonly performed as part of a comprehensive eye examination to determine refractive errors.

When light incorrectly refracts inside the eye, it causes refractive errors. This results in blurry vision or reduced visual acuteness. The fault may be in the eye lens, cornea, or size of the eyeball.

What happens during the refraction test?

During a refraction test, the doctor asks the patient to look through a device called a phoropter or refractor that contains wheels with different lenses of different strengths.

Each eye is examined separately to determine if the patient has a refractive error. While looking through the lenses of the phoropter, the patient will read the standard eye chart at 20-feet distance. The doctor will quickly change the lenses in the phoropter to help determine which combination gives the sharpest vision.

Children may need eye drops for paralyzing the muscles of accommodation (muscles around the eye lens that help us focus) before undergoing vision testing.

A chart called Snellen’s chart can also be used to test the alphabets, numbers, and images of various sizes that the patient can read from a 6-feet distance. Another chart can be used for reading at the near distance.

What can a refractive test find?

A refraction test not only determines if a person needs corrective lenses and the power of lenses but also if a person has a number of conditions such as:

  • Myopia or nearsightedness: Things can be seen clearly when they are close by but not when they are far away. This occurs when light doesn’t focus close enough to the retina.
  • Hyperopia or farsightedness: The opposite of myopia, hyperopia means objects that are far away can be clearly seen but not close by objects. This happens when light focuses too far past the retina.
  • Astigmatism: A misshapen cornea causes light to spread and make objects appear out of focus. Both nearby and far-away objects look blurry to people with astigmatism.
  • Presbyopia or age-related farsightedness: Over time, the eyes deteriorate at focusing and nearby objects start to look blurry. This happens usually after 40 years of age.

Why should regular refraction tests be done?

Eye examinations are an important part of preventive healthcare because many problems related to the eye and vision develop gradually, and a person (or a child) may not realize their vision is getting poorer. Early diagnosis and treatment of eye and vision problems are imperative to preserve healthy eyes, maintain good vision, and prevent vision loss.

Schedule of refraction test:

  • A routine eye examination should be performed every 3-5 years if there are no problems.
  • An eye examination should be scheduled immediately if vision becomes blurry or if there are any noticeable changes.
  • After the age of 40 years, eye examinations should be scheduled at least once a year.
  • For people with a family history of glaucoma, eye examinations should be scheduled once a year to test for glaucoma.
  • Anyone with diabetes should have an eye examination at least once a year.
  • People with a refractive error should have an eye examination every 1-2 years or whenever their vision changes.

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References
https://www.ucsfbenioffchildrens.org/tests/003844.html

https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/refractive-errors

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