Reading a glasses prescription can look confusing at first. Terms such as SPH, CYL, AXIS, ADD and PD each describe different parts of your prescription and lens requirements.
Quick answer: SPH refers to the spherical lens power used to correct nearsightedness or farsightedness. CYL and AXIS describe astigmatism correction, while ADD refers to additional near-vision power commonly used in multifocal prescriptions.
This guide explains the most common glasses prescription terms and how to understand the information on an existing prescription when ordering prescription eyewear online.
A glasses prescription should be provided by a qualified eye-care professional. This guide is for understanding an existing prescription and does not replace an eye examination or professional advice.
The Key Eyeglass Prescription Terms Explained
A glasses prescription contains the lens measurements and values needed to specify the optical correction for each eye. Common fields include OD, OS, SPH, CYL, AXIS, ADD and, when provided, PD. Here is what each column means:
1. What Do OD and OS Mean on a Glasses Prescription?
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OD (Oculus Dexter) refers to the right eye.
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OS (Oculus Sinister) refers to the left eye.
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OU (Oculus Uterque) refers to both eyes when the same notation applies to both.
2. What Does SPH Mean on a Glasses Prescription?
Indicates the overall lens power required to correct your vision, measured in Diopters (D).
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Minus Sign (–): Indicates Nearsightedness (Myopia) — you see well up close, but distant objects appear blurry.
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Plus Sign (+): Indicates Farsightedness (Hyperopia) — distant vision is clear, but close-up text requires effort.
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Note: In general, a larger absolute SPH value indicates a higher spherical lens power. For example, -5.50 represents a stronger spherical lens power than -1.25.
3. What Does CYL Mean on a Glasses Prescription?
CYL stands for cylinder and indicates the amount of cylindrical lens power prescribed for astigmatism correction. It may appear as a positive or negative value depending on the prescription format.
How to Read the CYL Value
CYL indicates the amount of cylindrical lens power used for astigmatism correction. It may be written as either a positive or negative value depending on the prescription format.
When entering CYL online, use the value exactly as it appears on your prescription. Do not change the sign or convert the prescription yourself unless instructed by your eye-care professional or eyewear provider.
How CYL and AXIS Work Together
CYL and AXIS work together when a prescription includes astigmatism correction. CYL indicates the amount of cylindrical lens power, while AXIS indicates the orientation of that correction in degrees. When both values appear on your prescription, enter them exactly as provided by your eye-care professional.
4. What Does AXIS Mean on a Glasses Prescription?
AXIS indicates the orientation of the CYL correction and is expressed in degrees, typically from 1° to 180°. It is used together with CYL when a prescription includes cylinder correction.
How to Read the AXIS Value
AXIS is recorded in degrees and indicates the orientation of the cylindrical correction used for astigmatism correction. It is used together with CYL when astigmatism correction is included in the prescription. It is used together with CYL when astigmatism correction is included in the prescription.
Enter the AXIS value exactly as shown on your prescription. Do not estimate or change the value when placing an order online.
5. What Does ADD Mean on a Glasses Prescription?
ADD (Addition) refers to additional lens power used for near vision. It commonly appears on prescriptions when additional near-vision correction is needed, including prescriptions used for multifocal or progressive lenses.
ADD is separate from the SPH, CYL and AXIS values. When ordering prescription eyewear, enter the ADD value exactly as it appears on your prescription.
How to Read the ADD Value
The ADD value represents additional near-vision power. If your prescription includes an ADD value, use the exact value provided by your eye-care professional rather than calculating a different number yourself.
The appropriate lens design depends on your complete prescription and visual needs.
For customers with ADD values, progressive lenses can provide clear vision at multiple distances without switching between different pairs of glasses.
Can You Use an ADD Value to Choose Reading Glasses?
An ADD value does not automatically determine a complete single-vision reading prescription. If you need dedicated reading glasses, use the near prescription provided by your eye-care professional rather than calculating a new prescription yourself.
Common Lens Features for Prescription Glasses
Prescription eyewear can be available with different lens designs and treatments depending on the frame and product configuration.
Common options may include single vision, progressive, photochromic, polarized and blue-light-filtering lenses. Availability can vary by product.
Before ordering, review the lens options shown on the specific product page and make sure the selected option is compatible with your prescription.
| Lens Feature | What It Does | When It May Be Considered |
|---|---|---|
| Anti-Reflective Coating | Helps reduce reflections from the lens surface | People who want less visible reflection |
| UV Protection | Helps reduce exposure to ultraviolet radiation | Outdoor use |
| Blue-Light Filtering | Filters selected wavelengths of visible light | Based on personal preference and lens specifications |
| Photochromic | Changes tint in response to certain light conditions | People who want an adaptive tint |
| Polarized | Helps reduce certain types of reflected glare | Outdoor activities and bright reflective environments |
Frequently Asked Questions
Q: Is My Contact Lens Prescription the Same as My Glasses Prescription?
A: No. A contact lens prescription and a glasses prescription are not interchangeable. Contact lenses require their own prescription and fitting information. Use the prescription specifically issued for your glasses when ordering prescription eyewear.
Q: What Does PD Mean on a Glasses Prescription?
A: PD stands for pupillary distance, the measurement used to help position prescription lenses in relation to the eyes. It may be provided as one binocular measurement or as separate measurements for each eye.
PD is an important measurement when ordering prescription glasses online. Learn how to measure your PD correctly before purchasing glasses from PHANEO. but it is not required to appear on every eyeglass prescription under the federal Eyeglass Rule. State requirements can differ. (FTC)
Q: What Does SPH Mean on a Glasses Prescription?
A: SPH stands for sphere and refers to the spherical lens power used to correct nearsightedness or farsightedness. It is typically recorded as a positive or negative value in diopters (D). If you are ordering prescription glasses online, understanding your SPH value helps ensure your lenses are made correctly. Learn more about how to order prescription eyewear online with PHANEO.
Q: What Does CYL Mean on a Glasses Prescription?
A: CYL stands for cylinder and indicates the cylindrical lens power used for astigmatism correction. It may appear as a positive or negative value depending on the prescription format.
Q: What Does AXIS Mean on a Glasses Prescription?
A: AXIS indicates the orientation of the cylindrical correction and is recorded in degrees. It is used together with CYL when astigmatism correction is included.
Q: What Does ADD Mean on a Glasses Prescription?
A: ADD stands for addition and refers to additional lens power used for near vision. It commonly appears on prescriptions that include additional near-vision correction.
Q: Can I Use My Glasses Prescription to Order Glasses Online?
A: You can use an existing glasses prescription when ordering prescription eyewear online if it is current and appropriate for your needs. Enter the prescription values exactly as provided and follow the eyewear provider's requirements for measurements such as PD.
How to Read a Glasses Prescription Example
A glasses prescription may contain several values for each eye. The following is a simplified example for explanation only and is not a real prescription.
| OD (Right Eye) | OS (Left Eye) | |
|---|---|---|
| SPH | -2.00 | -1.75 |
| CYL | -0.50 | -0.75 |
| AXIS | 90° | 180° |
| ADD | +1.50 | +1.50 |
| PD | 31.5 mm |
31.5 mm |
OD refers to the right eye, while OS refers to the left eye.
SPH indicates spherical lens power.
CYL indicates cylindrical lens power for astigmatism correction.
AXIS indicates the orientation of the cylindrical correction.
ADD indicates additional near-vision power when included in the prescription.
PD refers to pupillary distance and may be provided as a binocular measurement or separate measurements for each eye.
How to Enter Your Prescription When Ordering Glasses Online
Once you have an appropriate glasses prescription, follow the ordering instructions provided for the specific eyewear product.
You can explore PHANEO's prescription eyewear collection and choose a frame style before entering your prescription details.
Enter the values exactly as they appear on your prescription, including the plus (+) or minus (−) signs where applicable.
Depending on the product and ordering process, you may also be asked to provide pupillary distance (PD) and select a lens design such as single vision or progressive.
If you are unsure how to enter a prescription value, consult your eye-care professional or contact the eyewear provider before completing the order.