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How to Read a Glasses Prescription?

Understanding a glasses prescription is essential for those ...

Understanding a glasses prescription is essential for those who rely on prescription eyewear to correct their vision. These prescriptions are often a mix of numbers and abbreviations that can initially seem cryptic. Despite their complexity, they convey important information about the wearer’s visual needs. Interpreting these details empowers individuals to make informed choices about their eyeglasses.

A glasses prescription consists of different components, each representing a particular aspect of the lens correction required. The prescription typically includes indicators of lens power measured in diopters, which correct for nearsightedness or farsightedness. Astigmatism corrections and the necessary angle of adjustment, known as the axis, are also frequently detailed.

Specialized terms such as "sphere," "cylinder," and "axis" appear regularly in these prescriptions. These terms relate to the different types of correction required for an individual's vision. Sphere refers to the main lens power needed to correct vision, while cylinder and axis numbers provide specific details required to correct astigmatism. 

Understanding the Prescription Layout

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A glasses prescription contains specific measurements for correcting one's vision. To interpret these values correctly, one must understand the standard layout and what each section represents.

Sphere (SPH)

The Sphere (SPH) section indicates the power of the lens required to correct nearsightedness or farsightedness. Positive values denote farsighted correction, while negative values indicate nearsighted correction.

Cylinder (CYL)

Cylinder (CYL) measures the degree of astigmatism a person has and the lens power needed to correct it. Like the sphere, a negative value corrects for nearsighted astigmatism, and a positive value is for farsighted astigmatism.


The Axis defines the orientation of the astigmatism, marked in degrees from 0 to 180. This figure works in conjunction with the cylinder value to properly align the corrective power.

Pupillary Distance (PD)

Pupillary Distance (PD) refers to the distance, in millimeters, between the centers of the pupils in each eye. This measurement ensures that the lenses are properly centered over each eye.

Addition (ADD)

For bifocal or progressive lenses, the Addition (ADD) denotes the additional magnifying power applied to the bottom part of the lenses to aid in reading or close-up work. This number is always positive and can differ for each eye.

Decoding the Acronyms and Abbreviations

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OD and OS

"OD" (Oculus Dexter) and "OS" (Oculus Sinister) are Latin terms used to denote the right eye and the left eye, respectively. These are fundamental terms appearing in eyeglass prescriptions.

●OD (Oculus Dexter): Right Eye  
●OS (Oculus Sinister): Left Eye

Understanding these terms is crucial when interpreting the specifics of visual correction needs for each eye.


The abbreviation "OU" stands for "Oculus Uterque," a Latin term representing both eyes. In eyeglass prescriptions, it is a notation where the prescription applies equally to both eyes.

●OU (Oculus Uterque): Both Eyes

The presence of "OU" suggests there is a uniform corrective requirement for both eyes.

Prism and Base

"Prism" refers to the amount of prismatic power, prescribed to correct alignment issues with the eyes. The "Base" specifies the direction of the prism within the lens.

●Prism: Amount of prismatic correction  
●Base: Direction of the prismatic correction (e.g., Base Up, Base Down)

The prism and base work together to remedy binocular vision discrepancies, ensuring proper alignment and coordination between both eyes.

Identifying Lens Types

a pair of glasses and optical objects on a white background


When selecting eyewear, consumers must decide among different lens types that correct their vision based on the complexity of their prescription. These include single-vision, bifocal, and progressive lenses, each tailored for specific visual requirements.

Single Vision

Single vision lenses have one prescription power across their entire surface, catered specifically for correcting myopia (nearsightedness), hyperopia (farsightedness), or astigmatism. They are the most common and straightforward lens type, suitable for all ages.


Bifocals carry two distinct optical powers. The main part of the lens contains a distance prescription, while a smaller, lower segment is dedicated to reading or other close work. There is a distinct line across the lens that separates these viewing areas. 

Progre ssive

Progressive lenses offer a seamless graduation of varying lens powers, suitable for viewing at multiple distances. They eliminate the bifocal's visible line, providing a more natural transition from distance correction on the top to near correction on the bottom. These lenses accommodate an intermediate range as well, ideal for computer use.

Interpreting the Numbers

When reading a glasses prescription, the numbers define the corrective strength required for the lenses. They are crucial for creating eyewear tailored to an individual's vision needs.

Positive (+) and Negative (-) Values

The numbers on a glasses prescription will have either a positive (+) or negative (-) sign. These symbols indicate the type of refractive error. Positive values suggest that an individual is farsighted (hyperopia), meaning they see distant objects well but struggle with close-up tasks. In contrast, negative values denote nearsightedness (myopia), where close objects are clear, but there is difficulty in seeing objects at a distance.

These numbers are measured in diopters, representing the degree of correction needed to focus light onto the retina properly. For instance:

●A +2.50 indicates a farsighted prescription, requiring a converging lens.  
●A -3.00 signifies a nearsighted prescription, requiring a diverging lens.

Understanding these values is essential for accurately interpreting a prescription and providing the right lenses.

When to Consult a Professional

a professional consultant helps his client choose medical glasses


In the journey of eyewear prescription management, the individual must sometimes seek the expertise of an optometrist or ophthalmologist. Here are the scenarios where professional consultation is essential:

●Uncertain Interpretation: If there's any confusion about the meaning of the numbers or abbreviations on the prescription, a professional can provide clarity.


●Vision Changes: They should see a professional if they notice changes in vision, such as blurriness or eye strain, that aren't addressed by their current prescription.


●Prescription Expiration: Typically, eyeglass prescriptions have an expiration date. Upon expiration, they're advised to schedule a new examination to ensure the accuracy of their prescription.


●Physical Discomfort: If they experience discomfort such as headaches, dizziness, or eye pain with their current glasses, this indicates the need for a professional assessment.


●Lens Recommendations: Professionals can suggest the best types of lenses based on lifestyle and occupational needs, including progressive lenses, coatings, or tints.


Health Concerns: Eye health can impact prescription needs. They should consult a professional if they have conditions like diabetes or cataracts that can affect vision.

Jay Zhang

Jay Zhang, with over 5 years of experience, currently serves as the Sales Manager at JIANGSU MAAT OPTICAL TECHNOLOGY CO LTD. He specializes in research and development, as well as manufacturing, of photochromic lenses with a wide range of optional colors. In his role, Jay excels in marketing, customer-focused service, ensuring service quality, and enhancing the overall customer experience. His expertise lies in the commerce sector, contributing to the success of the company in the dynamic Chinese market since January 2023.

Learn More About Jay Zhang

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