How to Read Your Eye Prescription: Glasses and Contact Lenses Explained

Reviewed by Chris Day (Optician) and Dr. Justin Asgarpour (Optometrist).**

Are you deciphering your glasses or contact lens prescription? Understanding your eye prescription is simpler than you might think. This guide will break down all the numbers and abbreviations, empowering you to confidently shop for eyewear online or understand your vision needs.

It’s crucial to remember that glasses and contact lens prescriptions are distinct. A glasses prescription is specifically for eyeglasses and lacks information needed for contact lenses. If you wear contacts, ensure you have a separate contact lens prescription.

Continue reading to learn everything you need to know about how to read your eye prescription, whether it’s for glasses or contact lenses.

Understanding Your Eyewear Prescription: Common Questions

Let’s address some frequently asked questions about glasses and contact lens prescriptions. This guide will help you understand how to read glasses prescriptions and contact lens prescriptions effectively. If you encounter any difficulties, our Customer Service team is ready to assist and can even contact your Eye Care Provider to verify your prescription details.

Decoding the Numbers and Letters on Your Prescription

Your eye prescription contains specific terms and numbers that detail your vision correction needs. You might see abbreviations like SPH, CYL, Axis, ADD, and Pupillary Distance (PD).

These parameters are essential for correcting your vision, and PD is a critical measurement for crafting your glasses accurately. Let’s break down each component of your glasses prescription:

1. OD (Oculus Dexter): Refers to your right eye. The measurements following ‘OD’ are for your right eye’s vision correction.

2. OS (Oculus Sinister): Indicates your left eye. The values listed under ‘OS’ pertain to your left eye’s prescription.

3. SPH (Sphere): This indicates the primary lens power required to correct your vision, measured in diopters (D).

   • A minus sign (-) before the number signifies nearsightedness (myopia), meaning you have trouble seeing distant objects clearly.
   • A plus sign (+) or no sign indicates farsightedness (hyperopia), meaning you have difficulty seeing near objects clearly.

4. CYL (Cylinder) & AXIS: These values correct for astigmatism, a condition where the cornea or lens is irregularly shaped, causing blurred vision at all distances.

   • CYL indicates the amount of lens power needed to correct astigmatism. It always accompanies an AXIS value.
   • AXIS specifies the orientation of the astigmatism correction, measured in degrees from 1 to 180.

5. ADD (Addition): This value represents the added magnifying power needed for near vision, primarily for reading, and is used in bifocal, multifocal, and progressive lenses.

   • The ADD value is usually the same for both eyes and typically ranges from +0.75 to +3.00 D.
   • Lower ADD powers (below +0.75 D) may be prescribed for anti-fatigue lenses, like SightRelax lenses, to reduce eye strain.

Typically, prescriptions are separated for the right eye (OD) and left eye (OS), with each eye’s specific parameters listed. Some glasses prescriptions may also include:

6. Prism: Measured in prismatic diopters (p.d.), prism correction is needed when there’s an eye alignment issue. It helps correct double vision. Prism values are indicated with:
   • BO (Base Out)
   • BU (Base Up)
   • BI (Base In)
   • BD (Base Down)

These abbreviations indicate the direction of the prism base, which is the thickest edge of the prism lens. Please note that Clearly does not currently offer prism correction glasses.

Pupillary Distance (PD): An essential measurement for eyeglasses, PD is the distance between the centers of your pupils in millimeters (mm). It ensures the optical center of your lenses is precisely aligned with your pupils for optimal vision and comfort. If your PD is not on your prescription, you can learn how to measure your pupillary distance online.

Understanding Your Glasses Prescription Numbers

Once you understand these sections, reading your glasses prescription becomes straightforward.

• Minus sign (-) in SPH indicates nearsightedness.
• Plus sign (+) or no sign in SPH indicates farsightedness.
• An ‘ADD’ value signifies the need for magnifying lenses, like progressive lenses, to correct presbyopia (age-related near vision loss).

When ordering glasses online, simply input the numbers from your prescription into the corresponding fields on the website.

For example, consider this prescription:

OD: Sphere -2.50, Cylinder -0.75, Axis 173, ADD +2.25
OS: Sphere -3.00, Cylinder -1.00, Axis 004, ADD +2.25

This prescription indicates:

• Right eye (OD): Corrects nearsightedness (-2.50 SPH), astigmatism (-0.75 CYL, Axis 173), and near vision (ADD +2.25).
• Left eye (OS): Corrects nearsightedness (-3.00 SPH), astigmatism (-1.00 CYL, Axis 004), and near vision (ADD +2.25).

The presence of the ADD value indicates this is a multifocal prescription. Without the ADD value, it would be a single vision prescription.

Here’s how you would typically enter these values when purchasing glasses online:

Single Vision, Bifocal, and Progressive Lenses: What’s the Difference?

Understanding the types of lenses available will help you better interpret your prescription. Here’s a breakdown of the main lens categories:

1. Single Vision Lenses: The most common type, single vision lenses provide one correction across the entire lens. They are used for correcting nearsightedness, farsightedness, astigmatism, or for reading glasses.

2. Bifocal Lenses: Bifocal lenses have two distinct viewing areas. The upper part corrects distance vision, and the lower segment corrects near vision, separated by a visible line.

3. Progressive Lenses: Also known as no-line bifocals or multifocal lenses, progressive lenses offer a gradual transition of vision correction from distance at the top to near vision at the bottom, with intermediate vision in between. This provides a seamless and more natural visual experience.

Special Features and Enhancements on Your Prescription

Your eye prescription might also include recommendations for lens coatings or special features to enhance your vision and glasses.

1. Lens Designs: Your prescription may specify a lens design (single vision, progressive, bifocal) and sometimes even a specific brand recommendation for progressive or single vision lenses. These are often suggestions based on what the doctor’s office carries. If you have any questions about these recommendations, contact our customer service team.

2. Vision Enhancements: These are special lens treatments that improve vision clarity and comfort. Common options include:

   a. Anti-Reflective Coating: Reduces glare and reflections, allowing more light to pass through the lenses for clearer vision, especially at night and under fluorescent lighting.

   b. UV Protection: Protects your eyes from harmful ultraviolet (UV) rays from the sun, preventing potential long-term eye damage.

   c. Transitions Lenses: Also known as photochromic lenses, Transitions lenses automatically adjust their tint based on light conditions. They darken in sunlight and become clear indoors, offering both vision correction and sun protection.

   d. Polarized Lenses: Polarized lenses reduce glare from reflective surfaces like water, snow, and roads, providing enhanced clarity and visual comfort, particularly for outdoor activities.

   e. Clip-on Glasses: These are additional lenses that can be attached to your prescription glasses, often polarized or tinted, to provide sunglasses functionality or other vision enhancements.

   f. Blue Light Filtering Glasses: These lenses have a special coating that filters out blue-violet light emitted from digital screens and sunlight. They can help reduce eye strain and improve sleep. Clearly’s blue light glasses also offer scratch-resistance and anti-glare properties.

Understanding Your Contact Lens Prescription

Remember, glasses and contact lens prescriptions are not the same. To purchase contact lenses, you need a separate contact lens prescription from your eye care professional. In addition to the parameters found on a glasses prescription, a contact lens prescription includes Base Curve (BC) and Diameter (DIA), among other details.

Key Differences: Base Curve (BC) and Diameter (DIA)

To identify if you have a contact lens prescription, look for these additional specifications:

1. Base Curve (BC): This number indicates the curvature of the contact lens, designed to match the curve of your cornea. It ensures the lens fits comfortably and securely on your eye.

2. Diameter (DIA): This measurement specifies the overall size of the contact lens in millimeters, ensuring it properly covers your cornea.

3. Brand: Your eye doctor will prescribe a specific brand and type of contact lenses based on your individual needs, vision correction, and eye health.

4. Expiration Date: Contact lens prescriptions have an expiration date, usually one year from the date of your eye exam. After this date, you’ll need a new eye exam and prescription to purchase more contact lenses.

5. Corrective Power: Similar to glasses prescriptions, contact lens prescriptions include power values (SPH, CYL, Axis, ADD if applicable) but these values may differ from your glasses prescription.

If your prescription includes BC and DIA, it’s a contact lens prescription.

Base Curve (BC) and Diameter (DIA) are crucial for ensuring proper contact lens fit, comfort, and eye health by allowing adequate oxygen flow to the cornea. This information is essential when you order contact lenses online.

Ready to Shop with Your Eye Prescription?

Now that you understand how to read your eye prescription, you’re ready to explore eyewear options. Learn how to buy glasses online at Clearly and easily order your new glasses or contact lenses.

Browse our wide selection of stylish and affordable glasses and find the perfect pair for your vision needs and style.

Prefer contact lenses? Explore our wide selection of contact lenses and have them conveniently delivered to your doorstep.

If you have further questions about reading your eye prescription, our Customer Service team is here to help via email, live chat, or phone.

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