Refraction Test (Eye Refraction)
What is a Refraction Test?
A refraction test is part of a routine eye examination that measures an individual’s prescription for eyeglasses or contact lenses using a device called a phoropter. This test assesses how light is refracted from the eye and looks for any signs of a refractive error that may affect your vision. Normal vision acuity in a person is described as 20/20 vision (known as perfect vision), which means a person can read letters placed 20 feet (6.1 m) away.
What is Eye Refraction?
Eye refraction refers to how light rays refract as they pass through the eye to reach the retina. The light bends due to the properties of the eye’s lens and cornea, allowing the light to be precisely focused onto the retina to ensure clear vision. The light then reaches the light-sensitive cells (photoreceptors) of the retina, capturing the images and transmitting them via the optic nerve to the brain for interpretation.
The pupil widens or constricts to regulate the amount of light entering the eye and reaching the retina. In dim light, the pupil will dilate to allow more light in, while in bright conditions it constricts to prevent you from being temporarily disoriented or blinded.
A refraction test assesses the amount of light refracted into the eye to determine your visual acuity. It can help determine whether light is refracted correctly onto the retina and detect any refractive errors that may affect your vision.
What Does a Refraction Test Look For?
Apart from determining the degree of vision correction you need, the refraction test is instrumental to identifying (and correcting) the following conditions:
Astigmatism
This condition is characterised by an irregular curvature of the eye, where light focuses on multiple points on the retina, leading to blurry vision.
Myopia
Also known as nearsightedness, myopia occurs when light refracts onto a point in front of the retina, which causes distant objects to appear blurry.
Hyperopia
Also known as farsightedness, this condition causes light to refract onto a point behind the retina, resulting in nearby objects appearing blurry.
Presbyopia
Also known as “age-related farsightedness,” presbyopia occurs naturally as we age. This condition leads to a loss of elasticity in the eye’s lens, which makes it difficult to focus light on the retina. As a result, it causes blurry vision and eye strain.
Who Should Undergo a Refraction Test?
A healthy person under the age of 60 with no existing vision issues is generally recommended to undergo a refraction test every two years. Consider undergoing these tests as part of your long-term preventive care to help monitor and mitigate any developing refractive changes. Meanwhile, children between the ages of three and five should undergo a refraction test once, while those aged six and above should have annual vision checks.
Others that may undergo a refraction test include:
- Persons currently wearing eyeglasses or contact lenses: A refraction test can help correct your current vision.
- Persons with diabetes: Diabetes may increase the risk of eye conditions, such as diabetic retinopathy.
- Anyone with a family history of glaucoma: Glaucoma causes a gradual increase in eye pressure, which may damage the retina and the optic nerve.
- Senior citizens above the age of 60: The refraction test may help to detect vision problems associated with ageing and treat them promptly.
How a Refraction Test Works
An optometrist or ophthalmologist will conduct a refraction test using a computerised instrument, called an autorefractor, that measures the amount of light reflected by the retina. Alternatively, they may use a handheld retinoscope to shine a light into each of your eyes and determine how the light reflects off the retina. Both methods will produce a refractive score based on how light reflects off the retina.
The next part of the test involves the phoropter. The optometrist or ophthalmologist will instruct you to position yourself so that you can look through the phoropter’s eye slits. You should see a chart with letters on the wall ahead of you, typically at a distance of 20 feet. This test will assess one eye at a time.
While looking through the phoropter, you will be asked to read a specific row of letters to assess your visual acuity, or how sharply you can see the letters. The optometrist will then switch the phoropter’s lenses and ask if the new lenses provide clearer vision than the last ones. The same process will be repeated for the other eye.
Once this test is completed, the optometrist or ophthalmologist will review the results and provide you with the prescription. They will use the results to ensure your new corrective eyeglasses or contact lenses provide optimal visual clarity that is close to 20/20 vision.
Take Care of Your Eye Health with Philip D. Izaac
Early eye screenings are important for detecting and treating refractive errors early. At Philip D. Izaac, comprehensive vision care allows you to participate in various activities with friends and loved ones. Contact us today to find out more about our services.