The series of numbers stamped discreetly on the inside of your glasses frames often look like a secret code, leading many people to believe they contain their vision correction prescription. These markings are, in fact, an industry-standard reference system that has nothing to do with your optical power. The sole purpose of these digits is to provide precise measurements for the frame itself, ensuring a proper fit and allowing for accurate reordering or repairs. Understanding this code is the first step in decoding the true information held within your eyewear.
The Purpose of Frame Numbers
The primary numbers found on the temple arm or the bridge of your glasses are known collectively as the frame size. These standardized measurements are essential tools used by opticians and frame manufacturers globally, ensuring that the physical frame dimensions are consistent for every pair produced within a specific model line.
These measurements are fundamental for achieving a comfortable and secure fit on the wearer’s face. Small differences can drastically change how the glasses rest, preventing issues like slipping or uncomfortable pressure points. When replacing a broken frame or purchasing a new pair, these numbers act as the unique identifier for the frame’s physical size.
The sequence typically consists of three numbers separated by a dash or a small square symbol, such as “52-18-140.” These three values are always expressed in millimeters and define the three most important physical dimensions of the frame. They are the lens width, the bridge width, and the temple arm length.
Decoding the Measurements
The first number in the sequence is the Eye Size, or lens width, which specifies the horizontal width of the lens opening within the frame. This measurement, commonly ranging between 40 mm and 60 mm, determines the overall width of the lens itself and how much of your face the frame will cover. A larger eye size generally corresponds to a wider frame, affecting the aesthetic and the lateral fit on your head.
The second number is the Bridge Width, which measures the shortest distance between the two lenses where the frame rests across the nose. This measurement is crucial for comfort, as an incorrectly sized bridge can cause the frame to pinch the nose or slide down constantly. It directly influences how high or low the glasses sit on the face and how the weight is distributed.
The third number is the Temple Length, which measures the entire length of the arm piece from the frame’s hinge to the very tip that rests behind the ear. Standard temple lengths usually range from 120 mm to 150 mm. A correctly sized temple length is necessary to keep the glasses firmly in place during movement.
Understanding Other Frame Markings
Beyond the core three size measurements, you will often find other letters and numbers stamped elsewhere on the frame, particularly on the inside of the temple arm. These additional codes are not related to the frame’s physical fit but serve as inventory and manufacturing identifiers, primarily used by the optical company for tracking and ordering purposes.
Model and Color Codes
One of the most common markings is the manufacturer’s Model Number, a unique alphanumeric identifier for the specific style or design of the frame. This number allows manufacturers and retailers to distinguish between different frame shapes and materials within a product line. You may also see a Color Code, which specifies the exact tint or pattern of the frame material, such as “Havana” or “Matte Black.”
Lens Height (B-Measurement)
Sometimes, a fourth number will be included, which represents the lens height, or “B-measurement,” measured vertically at the lens’s widest point. While not always present, this measurement is particularly relevant for progressive or bifocal lenses, which require a certain minimum vertical space to accommodate the different viewing powers.
Where to Find Your Vision Prescription
It is a common misunderstanding that the numbers on the frame correspond to the patient’s vision correction, but the actual vision prescription is found only on a separate document. This prescription, or Rx slip, is provided by your eye care professional after a comprehensive eye examination. It is a medical record that details the optical power required to correct your specific refractive errors.
The prescription is organized into columns with standardized abbreviations, starting with OD (Oculus Dexter) for the right eye and OS (Oculus Sinister) for the left eye. The main power needed for distance or near vision is listed under SPH (Sphere), measured in diopters, indicating the degree of nearsightedness or farsightedness. A minus sign denotes correction for distance vision, while a plus sign indicates a need for reading or near vision correction.
If you have astigmatism, your prescription will also include numbers under CYL (Cylinder) and Axis. The cylinder value specifies the lens power needed to correct the astigmatism, while the axis is a number between 1 and 180 that denotes the orientation of that corrective power. Finally, a value under ADD (Addition) indicates the extra magnifying power needed for reading, typically for those over the age of 40.