How to Read an Eyeglasses Prescription

Published on July 17th, 2023

Updated on March 25th, 2024

Reading and understanding an eyeglasses prescription can be difficult for those unfamiliar with the optometry profession and the scientific terms they use. Some of the terms and abbreviations you may encounter on a glasses prescription include PD (pupillary distance), cylinder (CYL), sphere (SPH), axis, add and prism. Cylinder in an eye prescription refers to the amount of astigmatism a person has. Another pair of abbreviations include OD and OS which refer to the right and left eye respectively. These are Latin abbreviations used in a glasses prescription in certain countries although in Australia, we typically refer to them as the right and left eye. An eye prescription chart is a piece of paper or digital copy that holds information about a patient’s vision.

An eyeglasses prescription represents a person’s vision and what is required to correct their eyesight. The purpose of a prescription is to provide the patient with clear and comfortable vision by supplying the correctly powered lenses. Generally, you won’t need to know how to read a prescription for glasses, as this is the role of the optometrist and optical dispenser.

Four ways to help a person read an eye prescription are familiarising yourself with eye prescription abbreviations, identifying the right and left eye on the prescription, understanding the eye prescription scale or range and looking out for additional eye prescription values. The ways to read an eyeglasses prescription are listed below.

Familiarise yourself with eye prescription abbreviations:Familiarising yourself with eye prescription abbreviations can help you understand how your vision is being corrected. Some abbreviations include SPH, CYL and PD.
Identify the right and left eye: Identifying the right and left eye on a prescription can sometimes be difficult as they can be denoted using Latin abbreviations, OD and OS.
Understand the eye prescription scale or range: An eye prescription scale or range shows the plus and minus sphere values that represent nearsightedness and farsightedness.
Look for other additional eye prescription values: There are other additional eye prescription values that people may not be aware of their meanings. These include axis, add and int add.

1. Familiarise Yourself With Eye Prescription Abbreviations

Familiarise yourself with the eye prescription abbreviations to understand what your eyes require to see comfortably and clearly. The common eye prescription abbreviations include SPH, CYL and PD and they are listed below.

SPH (Sphere): SPH is an abbreviation for sphere. On a glasses prescription, SPH indicates the amount of nearsightedness and/or farsightedness a patient has, which is written as a number showing the lens power measured in diopters. Sphere is denoted with a plus (+) symbol for farsightedness and a minus (-) symbol for nearsightedness. These plus or minus numbers will determine the power of the lens needed to correct a patient’s vision.
CYL (Cylinder): CYL is an abbreviation for cylinder and on an eyeglasses prescription it represents the amount of astigmatism a patient has and is denoted with a minus (-) symbol. Astigmatism is corrected using a CYL lens which is equal but opposite to the amount of astigmatism that is on the prescription.
PD (Pupillary Distance): PD is an abbreviation for pupillary distance and is the measurement in millimetres of the distance between a person’s eyes. It is used to ensure that your lenses are positioned properly to give you clear vision. At Oscar Wylee, a patient’s PD is not shown on their prescription, rather it is measured after their eye test by one of our retail staff.

The below image shows where the sphere and cylinder are on an Oscar Wylee prescription.

Abbreviations on an Oscar Wylee glasses prescription

2. Identify the Right and Left Eye

In Australia, we make it easy to identify the right and left eye on a prescription by clearly noting it as Right Eye and Left Eye. However, in other countries like the US and Canada, they use OD and OS. According to the American Academy of Ophthalmology, these abbreviations are derived from Latin with OD standing for oculus dexter, which is the right eye, and OS standing for oculus sinister, which is the left eye.

The below image shows where the right and left eye are on an Oscar Wylee prescription.

Left and right eye on an Oscar Wylee glasses prescription

3. Understand the Eye Prescription Scale or Range

It can be useful to understand the eye prescription scale or range which shows the plus and minus values that denote the amount of nearsightedness or farsightedness a patient has. These values are shown under the abbreviation SPH which is short for sphere, on an eye prescription. The negative numbers represent nearsightedness and the positive numbers represent farsightedness.

The image below shows the eye prescription scale from -6.00 diopters to +6.00 diopters.

4. Look for Other Additional Eye Prescription Values

There are additional eye prescription values that you may be unaware of their meaning. Other eye prescription values include axis, add, int add and prism, which are listed below.

Axis: Axis is a number between 0-180 degrees which specifies the angle to correct astigmatism. Axis and CYL cannot occur without the other as they work together to correct astigmatism.
Add: Add, an abbreviation of addition, represents the amount of magnification required for near vision which is denoted with a plus (+) symbol. Add may be needed for reading glasses, bifocals and multifocals.
Int Add: Similarly to add, int add stands for intermediate addition which is the magnification needed for intermediate vision such as computer vision. Int add is approximately 70 cm away and is used in multifocal lenses as it is the prescription between near and distance vision.
Prism: Prism correction can be added to a patient's lenses if they experience double vision or have trouble focusing.

The below image shows where the axis, add and int add are on an Oscar Wylee prescription.

Additional values on an Oscar Wylee glasses prescription

What is an Eyeglasses Prescription?

An eyeglasses prescription is the amount of correction your vision requires in order to see clearly and comfortably. An eye prescription will be acquired through an eye test performed by an optometrist who will assess a patient’s vision to determine if they need vision correction and if they do, the type and power. For example, someone with farsightedness will need prescription glasses to make their near distance clear and vice versa for nearsightedness. There are also refractive errors such as astigmatism or presbyopia that can affect a person’s vision which will be noted on their prescription.

Once a person receives their prescription, the optometrist will hand it over to an optical dispenser who can help the patient find the right pair of lenses for their prescription needs. This could mean purchasing a pair of reading glasses or multifocal lenses.

How Does an Eyeglasses Prescription Work?

An eyeglasses prescription works by noting the amount of correction a patient’s vision needs using numbered values with either a plus or minus. There is also a number in degrees that notes the degree of axis needed to correct astigmatism. A glasses prescription will be handed over from the optometrist to an optical dispenser to interpret and then find the right pair of lenses for the patient. The ultimate purpose of a prescription is to give the patient clear and comfortable sight through vision correction.

What is the Importance of an Eyeglasses Prescription?

An eyeglasses prescription is very important for people who need vision correction. A prescription specifies the exact strength needed to correct a person's vision and will inform what lenses should be put into their glasses. Without a prescription, you will not be able to purchase a pair of optical glasses that will give you clear and comfortable vision.

What is a Normal Eyeglasses Prescription?

There is no such thing as a normal eyeglasses prescription as each person requires a prescription based on their own eyesight and eye health needs. However, in terms of visual acuity, which measures the sharpness and clarity of a person’s vision, 20/20 vision is used as a way to quantify normal vision. If a person has 20/20 vision, it means they can see an object clearly twenty feet away or 6 metres. This measurement is determined by reading letters on an eye chart, commonly a Snellen chart.

While 20/20 vision is considered normal, people can have better visual acuity. For example, a person could have 20/15 vision which means they can see clearly at 20 feet what a person with 20/20 vision would need to be 15 feet away to see. A person with 20/20 vision will most likely not need corrective lenses although they may require an eye prescription if there are other visual issues such as astigmatism.

What Does +1.25 Mean on Eyeglasses Prescription?

The value +1.25 diopters on an eyeglasses prescription means the patient has a minor level of farsightedness, meaning they may experience blurriness in their near vision when reading or doing other close-up tasks. A sphere of +1.25 diopters can be corrected with prescription glasses that can be provided by an optometrist.

What is the Eyeglasses Prescription for Nearsightedness?

An eyeglasses prescription for nearsightedness will have a sphere (SPH) value denoted with a minus (-) symbol meaning the eye prescription requires a minus-powered lens. According to the American Academy of Ophthalmology, mild nearsightedness lens prescription is typically 3.00 diopters and below, moderate is 3.00-6.00 diopters and severe nearsightedness is 6.00 diopters and above.

Nearsightedness, known scientifically as myopia, is a refractive error that affects distance vision due to an overly curved cornea or an elongated eyeball. A person with nearsightedness will have eyes that are not capable of bending and focusing light on the retina correctly. The lenses used to correct nearsightedness are concave lenses which correct the focal issues and give the wearer clear and comfortable vision. Wearing eyeglasses will not cure nearsightedness, rather they will correct the vision issue through a prescription lens.

What is the Eyeglasses Prescription for Farsightedness?

An eyeglasses prescription for farsightedness will have a sphere (SPH) value denoted with a plus (+) symbol meaning the eye prescription requires a plus-powered lens. The lenses that correct farsightedness are called convex lenses or plus lenses. Convex lenses are characterised by their thick centre that helps light focus back onto the retina. According to Central Oregon Eye Care, the prescription for mild farsightedness is +2.00 diopter or less and +6.00 diopter and over is considered an extreme farsightedness prescription.

Farsightedness, known scientifically as hyperopia, is a refractive error that occurs when light does not reflect within the eye correctly, making it difficult for the eyes to clearly and sharply see objects at near distances. Symptoms of farsightedness include blurry near vision, eye strain and headaches. Farsightedness cannot be cured with prescription lenses, rather it is corrected which means the lenses help direct the light that enters the eye onto the retina.

What is the Eyeglasses Prescription for Astigmatism?

On an eyeglasses prescription, CYL (cylinder) represents the amount of astigmatism which is denoted with a minus (-) symbol. According to Vision Centre, mild astigmatism is 1.00 diopter and below, moderate is 1.00-2.00 diopter, severe is 2.00-3.00 diopter and extreme is 3.00 diopter and above. Astigmatism is corrected using a CYL lens which is equal but opposite to the amount of astigmatism that is represented on the patient’s prescription.

Astigmatism is a type of refractive error that occurs when the cornea or lens on a person's eye is deformed or misshapen which disrupts the eye’s ability to focus light onto the retina. Uncorrected astigmatism can cause blurry vision, poor night vision and headaches. It is possible to have astigmatism and other refraction errors, such as myopia (nearsightedness) or hyperopia (farsightedness) at the same time.

What is Considered a Bad Eyeglasses Prescription?

There are not necessarily bad and good eyeglasses prescriptions, rather some people may require a stronger prescription to correct their vision while others may need less or no vision correction.

What is the Duration of Validity for an Eyeglasses Prescription?

The duration that a glasses prescription is valid for is typically 1-2 years. The expiry for a prescription can vary from person to person due to contributing factors such as existing eye conditions and age. For example, an older person may have a shorter expiration on their prescription as their vision is more likely to decline as they age. To find out when your prescription expires, it will be noted on your prescription or you can check with your optometrist.

When to Update a Glasses Prescription?

A person should update their glasses prescription when it expires. At Oscar Wylee, we recommend everyone should have an eye test at least once every two years. For those over the age of 65, a yearly review is advised. Having a regular eye test allows an optometrist to monitor any changes in your vision which may require an updated prescription. They can also monitor the progression of eye conditions you may have.

While having an eye test at least once every two years is a good schedule to follow, there are other signs that may indicate you need a new glasses prescription. These signs include vision changes such as blurry or double vision, difficulty focusing, squinting, eye strain when wearing glasses, not having regular eye tests and poor night vision.

How Often Does an Eyeglasses Prescription Change?

There is no definitive answer for how often an eyeglasses prescription changes as it can vary from person to person. For some it could be years, for others, it may be longer or even less. There are certain factors that can impact how quickly a prescription can change including age as there are many age-related eye conditions that cause a person’s eyesight to decline. This includes presbyopia which affects near vision and cataracts which occur due to age-related changes in the lens. Existing refractive errors may also be a factor such as astigmatism which causes blurry vision due to the irregular shape of the eyeball.

If you have noticed any significant changes in your vision, book an eye test with an optometrist.

Can Wearing Lower Prescription Glasses Damage the Eyes?

No, wearing lower prescription glasses will not damage the eyes, although it is not recommended as it could cause eye strain and discomfort. People should also refrain from wearing other people's glasses even if they think they have the same prescription. This is because a prescription is more than simply the correction for near or farsightedness, it could also contain correction for astigmatism or even a prism lens. If you think your glasses prescription is too low or you are having trouble with your lenses, come and visit an Oscar Wylee near you where we can help update your prescription and glasses if needed.

Can I Use an Expired Glasses Prescription to Buy New Glasses?

No, you cannot use an expired glasses prescription to buy new glasses as they will not be accepted by the optometrist or retail staff. If you need a new pair of glasses, you will be required to have your eyes tested to receive a new prescription. An expiration date on a prescription ensures you have your eyes regularly tested as it is common for vision to deteriorate over time.

Wearing glasses that have an outdated prescription can cause eye discomfort such as eye strain and headaches and may also cause blurry vision if the prescription is no longer strong enough to correct your vision. We do not accept expired prescriptions at Oscar Wylee, but you can easily book an eye test appointment in-store with one of our friendly optometrists to receive an updated prescription that you can use to either update your lenses or order a new pair of glasses.

Read How to Read an Eyeglasses Prescription in other Oscar Wylee regions and their languages.