Refraction Test: Principles of Refraction Eye Exam, Benefits, Procedures

Published on May 15th, 2024

Updated on September 06th, 2024

A refraction test, also referred to as a vision test is normally performed as part of a routine eye test and informs the optometrist if a patient requires prescription glasses or contact lenses. For patients with normal vision, their cornea and lens should be capable of refracting incoming light so it is positioned directly on the retina. However, if you have a refractive error, the light is not bent correctly when passing through the eye causing blurry vision. Refraction is the bending of light when passing from one object to another, which occurs in the eye through the cornea and lens. If you are experiencing blurry vision and do not already use prescription glasses, it is important to have an eye test in order to have a refraction eye exam performed. At Oscar Wylee, eye tests are bulk billed for eligible Medicare card holders.

What is Refraction in an Eye Exam?

Refraction in an eye exam is defined as a measure of what type of prescription you require or if a prescription is needed at all. Refraction in an eye test enables the optometrist to evaluate how well your eye bends light as it passes through the eye and where the light lands in relation to your retina.

What is the Purpose of Refraction in an Eye Exam?

The purpose of refraction in an eye exam is to assess how the eye refracts light and whether you have any refractive errors. If you do have a refractive error, the light that passes through the eye is not correctly focused on the retina, resulting in eye problems such as myopia (nearsightedness), hyperopia (farsightedness), presbyopia (age-related farsightedness) and astigmatism.

$Diagram depicting incorrect refraction of light as a result of refractive errors, nearsightedness, farsightedness and astigmatism.$

What are the Basic Steps of a Refraction Test?

The basic steps of a refraction test include an auto-refraction or retinoscopy and a lens phoropter. The auto-refraction or retinoscopy portion of the process is the first step and involves measuring your distance vision by shining a light into your eye or using an auto-refractor. This enables the optometrist to evaluate how the light enters the eye and how the cornea and lens bend the light for it to reach the retina. The optometrist will then get you to look through a lens phoropter, which is a special device that features multiple combinations of lenses and dials. Looking through the lens phoropter will help the optometrist determine your prescription.

How Does a Refraction Test Work?

A refraction test works by using special instruments to examine how light rays are bent when entering the eye, which indicates if you have any refractive errors. An eye refraction exam begins with the optometrist using an autorefractor or manual refraction which enables them to assess the severity of your refractive error. The optometrist will also shine a light in your eyes while looking through the pupil and examine how the light reflects off the retina.

Why Should You Undergo a Refraction Test?

You should undergo a refraction test so an optometrist can identify any refractive errors and prescribe glasses for vision correction if deemed necessary. It is important to have a refraction test as part of your regular eye test if you are experiencing any signs such as blurry vision when looking at nearby objects or objects in the distance. Refractive errors can develop as a result of an abnormally-shaped cornea or lens, when the eyeball grows too long or too short and due to the ageing of the lens according to the National Eye Institute.

What are the Benefits of a Refraction Eye Exam?

The benefits of a refraction eye exam include identifying and correcting refractive errors and monitoring changes to a patient’s vision. A refraction eye exam is beneficial for detecting eye problems such as nearsightedness, farsightedness, age-related presbyopia and astigmatism. This allows the optometrist to prescribe the right glasses according to your vision requirements. For patients who already use prescription glasses, a refraction eye exam is important for monitoring possible changes that can naturally develop over time.

What is the Procedure for a Refraction Test?

The procedure of a refraction test usually requires an optometrist to use certain instruments such as an autorefractor or manual refractor, a phoropter and a Snellen chart. During a refraction test, the optometrist will examine how light moves through the lens and cornea in the eye, which may involve a computerised refractor or manual refractor. Using a computerised refractor will involve looking through a special machine to determine the amount of light reflected by the retina. The optometrist will then position you in front of a phoropter to look through and read letters from a chart 20 feet away. During this process, the optometrist will swap out different lenses and ask which lens option is clearer. After repeating this process on the other eye, the optometrist will then create a prescription that can provide 20/20 vision.

What Equipment is Used in Refraction Testing?

The equipment used in refraction testing can include a phoropter, an autorefractor and a Snellen chart. A refraction test usually involves an autorefractor, which measures the eye’s focusing ability and helps the optometrist determine your prescription. An auto-refractor removes the need for the patient to look at a chart or respond to which lens option is clearer and identifies refractive errors by observing how the light acts when entering the eye and reaching the retina. A phoropter features multiple lenses, which the optometrist goes through during your test to find the most suitable lens for your vision condition. A Snellen chart has rows of letters that differ in size and is used during a refraction test to evaluate how well you can see visual details and distinguish between the different shapes.

$Snellen chart on tablet device, autorefractor and phoropter.$

What do the Numbers in Your Prescription Mean?

The numbers in your prescription indicate diopters, which is a unit of measurement that represents the amount of correction you need for clear vision. Your prescription will have different columns of abbreviated terms such as ADD (magnification required for close vision), axis, SPH (sphere), CYL (cylinder), PD (pupillary distance) and int ADD (intermediate ADD). The numbers in your prescription will let the optical dispenser know what type of lenses to dispense according to your visual needs. Understanding prescriptions can be easier when you are familiar with the different terms such as ADD which you may have if you need reading glasses. Axis is the angle between 0 and 180 degrees required to correct astigmatism. CYL represents the amount of astigmatism you have denoted with a minus symbol and is corrected using a CYL (cylindrical) lens. SPH (sphere) signifies the amount in numerals of farsightedness denoted with a plus symbol or nearsightedness denoted with a minus symbol. It will determine the power of the lens you need for clear and comfortable vision. PD is the measurement of the distance between the pupils and is used to ensure that your lenses are positioned properly to give you clear vision. Int ADD represents the amount of magnification required for intermediate vision such as when looking at a computer, which is typically about 70cm away.

A glasses prescription indicating numbers from an eye test.

How are Eye Problems Diagnosed with a Refraction Test?

Eye problems are diagnosed through a refraction test as they allow the optometrist to examine how the light acts when passing through the eye and onto the retina. The optometrist is then able to confirm whether the incoming light is bent correctly so that it is directly on the retina. This will signify whether you have a refractive error and how severe it is. Refractive errors include nearsightedness (myopia), farsightedness (hyperopia), age-related farsightedness (presbyopia) and astigmatism. Reading from a chart of letters during your refraction test aids in indicating how well your eyes can see details in objects.

What Tests are Used to Diagnose Nearsightedness (Myopia)?

The tests used to diagnose nearsightedness can include a refraction test, a visual acuity test and a retinoscopy. These tests are normally part of a standard eye test, performed by an optometrist. To diagnose nearsightedness, an optometrist will use different tools to assess how your eyes focus light and measure the required amount of power for your prescription glasses. The optometrist will first examine your visual acuity by having you read letters out loud from a chart. They will then use a retinoscope to observe how your retina reflects light according to the Cleveland Clinic.

How Do Optometrists Identify Farsightedness (Hyperopia)?

Optometrists can identify farsightedness (hyperopia) during a standard eye test. Diagnosing farsightedness (hyperopia) usually involves a visual acuity test and a refraction test. A visual acuity test is an eye test that determines how sharp and clear your vision is. A visual acuity test will involve a person looking at a chart consisting of lines of letters that decrease in size. The patient will read the letters until their eyes cannot see clearly. The line that a person stops at will give them a score determining their visual acuity. A slit lamp test refers to an eye test conducted with a microscope that has a light. A refraction test is an eye test that will determine what prescription a person needs. An optometrist will have their patient look through a series of different lenses with varying magnification strengths to determine what level of vision correction they need.

What are the Common Methods For Detecting Astigmatism?

The common methods for detecting astigmatism usually require a visual acuity test, an autorefraction and retinoscopy refraction test, keratometry, pachymetry, and corneal topography. Optometrists may diagnose astigmatism if you are experiencing symptoms such as blurry or distorted vision at all distances. Similar to the process of diagnosing nearsightedness and farsightedness, astigmatism can be identified through a visual acuity test, refraction test and a slit-lamp exam but also keratometry, which uses an instrument known as a keratometer and measures the curvature of your cornea. A pachymetry is a test that assesses the thickness of the cornea. Corneal topography can be used to diagnose astigmatism as it is a photography technique that maps the cornea’s surface. Corneal topography works by allowing the eye care professional to identify distortions in the curvature of the cornea, according to the American Academy of Ophthalmology.

What Makes Refraction Tests Unique Compared to Other Eye Exams?

Refraction tests are unique to other eye tests as they are intended to examine how light rays pass through your eye, whether they are properly reaching the retina and how well you can identify details in objects. Other eye exams may typically look at eye movement, eye pressure and the physical nature of structures within the eye through scanning or special photography.

How are Refraction Tests and Visual Acuity Tests Different?

Refraction and visual acuity tests are not necessarily different, as a visual acuity test is carried out during a refraction test. A visual acuity test involves the use of a Snellen chart and indicates how well you can discern details from the objects you see.

What Should You Expect When Preparing for a Refraction Test?

When preparing for a refraction test, you should expect the optometrist to ask you questions regarding your eye condition and for several tests to be performed. Therefore, it may be helpful to think about your symptoms so you can easily present them to your optometrist during your appointment. Ensure your eyes are in optimal condition by getting enough sleep and avoiding long periods of screen time to not overexert your eyes. If you have any concerns about what to expect from an eye test, be sure to talk with your optometrist.

What are the Best Practices for a Successful Refraction Test?

The best practices for a successful refraction test may include ensuring that the procedures are time efficient, allowing sufficient time for patients to respond and having the right tools. These practices are recommended for the eye care professional carrying out the refraction test. The best practices for a successful refraction test are listed below.

Time efficient: An optometrist should ensure that the appointment is time efficient as it can be common for patients to lose focus over a certain period and therefore may not be capable of paying proper attention and provide inaccurate responses.
Allow sufficient time for patients to respond: Allow sufficient time for patients to respond when using the phoropter and swapping between different lenses to ensure they are confident with their answers.
Having the Right Tools: It is vital to have the right tools when conducting a refraction test to ensure the optometrist achieves optimal results.

How do Refraction Tests Vary Between Children and the Elderly?

Refraction tests may only vary between children and the elderly in how frequently these age groups need to be tested. Eye exams for children, with or without any existing eye conditions, are recommended once every two years unless advised otherwise by their optometrist. Elderly patients are typically recommended to have their eyes tested every year due to the natural changes that occur in the eye with increased age.

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