How to Understand Your Eye Prescription
Understanding the numbers, abbreviations, and symbols on your spectacle prescription is easier than it seems.
Once you know what each number or abbreviation represents, you can decode your spectacle or contact lens prescription.
Here is our simple guide to reading and understanding an optometrist's prescription, for both spectacle and contact lens prescriptions.
Key Summary:
The numbers, symbols, and abbreviations on your spectacle prescription represent the type of lenses you need and how strong the lenses need to be
Generally, each eye will have its own prescription, symbolised by OD or OS, or right and left eye
Contact lenses require a different prescription since they must be worn directly on the surface of the eye
Eye testing is the most effective way to maintain your eye health
Eye testing is fast, easy, and comfortable
You may experience changes in your vision, making regular checkups and eye testing an important step in ensuring your prescription is still accurate
How to Read an Spectacle Prescription
Here are simple ways to understand the numbers, symbols, and abbreviations on a spectacle prescription:
OD: OD is an older Latin Abbreviation used for “ocular dexter” in spectacle prescriptions and means right eye.
OS: OS is short for “ocular sinister” and means left eye.
Sphere (SPH): The abbreviation SPH refers to the sphere value. It tells the optometrist how much lens power is required to correct your eyesight. A plus sign by the SPH abbreviation indicates farsightedness (hyperopia). A minus sign represents nearsightedness (myopia).
Cylinder (CYL): A cylinder value (CYL) indicates the degree of astigmatism in your eye.
AXIS: The axis will be listed along with the cylinder value if you have astigmatism. AXIS is listed between 1 and 180 degrees and tells the optometrist where the astigmatism is located in your eye.
PD: PD stands for pupillary distance. It refers to the distance between the centre of each pupil. It is measured in millimeters and is a crucial way to determine where to look through the lens for the highest degree of comfort and clarity. PD is measured in relation to a frame chosen by a patient. Therefore, you may not have a PD measurement shown on a prescription if you have not had spectacles dispensed by an optometry practice.
ADD: ADD stands for Additional Lens Power and represents how much additional magnifying power is needed for near vision activities, such as reading or working on your laptop. This abbreviation applies equally to both eyes and is always a positive value, usually between +0.75 and +3.00.
Int ADD: "Int Add" stands for "intermediate addition". It specifies how much magnification is needed for intermediate vision activities and is usually used in prescriptions for intermediate distance lenses (computer use) or multifocal lenses.
PRISM: ‘Prism’ listed on your optometrist prescription details how much prismatic power is needed to correct double vision. It is measured in prismatic diopters (p.d).
A prism, like a pyramid, has a base and an apex. Noting the position of the base of the prism details how to position the prism on the spectacles to promote the eyes working together in proper alignment. It is indicated as follows: BO (Base Out, for horizontal alignment conditions, away from the nose), BU (Base Up for vertical alignment issues), BI (Base In, toward the nose, for horizontal alignment issues), or BD (Base Down for vertical alignment issues).
Spectacle Prescription Examples
Here are a couple of spectacle prescription chart examples so you know what to expect:
Patient: Rachel
| SPH | CYL | AXIS | |
|---|---|---|---|
| OD | -2.25 | -0.50 | x155 |
| OS | -3.00 |
Spectacle Prescription Explanation: Rachel’s optometrist will use this prescription to create spectacles that correct her nearsightedness and astigmatism.
Patient: Tom
| SPH | CYL | AXIS | |
|---|---|---|---|
| OD | -0.50 | sph | |
| OS | -0.75 | sph |
Spectacle Prescription Explanation: Tom’s prescription indicates that he has nearsightedness that needs to be corrected. The minus sign next to the SPH value represents nearsightedness.
How to Read A Contact Lens Prescription
Spectacle and contact lens prescriptions are different. Expect to see some additional parameters on your contact lens prescription.
In Australia, a contact lens prescription is a medical device prescription and it will have an expiry date. Make sure you check the expiry date as typically it will expire after 12 months.
Along with the general eye prescription parameters (OD, OS, PRISM, ADD, CYL, & AXIS), you will see Base Curve (BC) and Diameter (DIA).
The Base Curve (BC) number indicates the back surface shape of the contact lens based on the flatness or steepness of your cornea.
The Diameter (DIA) number indicates the width of the contact lenses required to be to cover your cornea appropriately and comfortably.
These parameters ensure the contact lenses fit your eye surface and cornea comfortably. They also ensure there is enough oxygen available to the eye.
Contact lens prescriptions may also include a specific brand. Each brand is constructed with varying lens materials that affect oxygen availability and fit. To switch brands, you’ll need to consult your optometrist.
Differences Between Contact Lens and Spectacle Prescriptions
As discussed, contact lenses and spectacles both work to correct refractive errors but the prescriptions are different. The main difference is that contact lenses sit directly on the surface of the eye. This requires careful consideration of how the contact lens is shaped. It needs to fit the curve of the eye and be the appropriate width to cover the cornea comfortably.
Along with the standard specifications on a spectacle prescription, an optometrist needs to know the Lens Diameter and Base Curve to create your contact lens prescription. Therefore, the power specified in a contact lens prescription can differ from that specified in the spectacle prescription.
Differences Between Progressive, Intermediate, Bifocal and Single Vision Spectacle Lenses
Here are the categories of lenses that may appear on your spectacles prescription and what they mean:
Single Vision Lenses — Single vision lenses include a single vision correction. They are a simple, common lens option used to correct farsightedness, nearsightedness, or to be used as reading spectacles.
Bifocal Lenses — Bifocal lenses come with two vision corrections. One lens on the lower part is dedicated to helping with near vision activities, such as reading. The other lens on the upper part is a distance prescription. Bifocal lenses are rarely prescribed today as most patients have adapted to progressive lenses.
Intermediate Lenses - Spectacle lenses focussed on an intermediate distance, such as that required to work at a computer.
Progressive Lenses —Multifocal or progressive lenses offer multiple corrections in one pair of spectacles and provide a progressive range of vision from distance to near.
Special Features
You may also find special features or additional information, such as vision enhancement features or certain lens designs.
Vision enhancement features may include options such as:
Anti-UV treated lenses to protect your eyes against damaging UV rays.
Anti-reflective coating to promote clarity and reduce reflection. This is particularly useful for driving at night time.
Blue-light blocking technology to filter out blue-violet light and UV rays that may be emitted from a computer screen.
Transition technology to automatically adjust the tint of your spectacles based on the ambient light levels.
Polarized lenses to improve focus, reduce glare, and promote clarity.
High index materials which have a higher bending power of light. They are thinner and lighter which aids ease of wear and aesthetically improves the look of the spectacles.
FAQs
What is an optometrist prescription?
An optometrist prescription is a written order detailing what is required to correct an individual’s eye condition. An eye prescription will typically detail which eye the prescription is for, the lens power needed, and any other necessary information. These details will be used to create corrective lenses that give you clearer vision.
Are eye prescriptions the same everywhere?
Spectacle prescriptions are considered universal, meaning they use a standardised format and common notations worldwide.
Are prescriptions the same for contacts as they are for spectacles?
No, prescriptions for contact lenses and spectacles are different. Because contact lenses need to fit the curve of the eye and the fact that the corrective power of the lens sits on the eye, rather than away from the eye, they are different than spectacle prescriptions.
Contact lens prescriptions take the diameter of the eye and the base curve of the eye into account to create an effective, comfortable fit. An expiration date and specific lens brand is typically included in the prescription as well.
How do I find out my spectacle prescription?
To find out your spectacles prescription, we recommend scheduling an eye test. This quick, comfortable exam is the most effective way to determine your vision needs.
How often does a prescription change?
Vision can change with time but there is no set range of how often an eye prescription changes. It is important to have regular eye exams to ensure your prescription is ideal for your current vision needs.
When should I update my prescription?
With time, your vision can change. Seeing your optometrist for regular eye testing and checkups ensures your prescription is still effective.
It is generally recommended to have an eye exam every 2 years unless advised otherwise by our optometrists.
Your Best Vision and Healthy Eyes
The numbers, symbols, and abbreviations on your eyeglass prescription are important indicators that detail how to correct your vision.
If you need help understanding your eye prescription or want to discover your clearest vision, schedule your eye exam with our caring team today. With over 30 years of experience, our established practice is highly regarded by our patients in the Fremantle area.
For Eyes Optometrists Fremantle is committed to ensuring you enjoy the best vision now and in the future. Book Your Appointment or schedule your eye exam today to start your journey toward your healthiest eyes.
