Ophthalmic Frames: Unraveling the Intricacies of the Measuring Systems
by Brianna Cuenca on October 14, 2024System of Frame Measurements
Eyeglass frame and lens measurements are a critical aspect of the optical industry. Frames may be measured using either one of two systems, the Datum System or the Boxing System.
The Datum System
When measuring an eye size using the datum system, an imaginary line is drawn through the middle of the eyewire both in the horizontal and vertical planes. The length of those lines corresponds to the horizontal and vertical measurements of the eyewire. Given a shape such as that illustrated below, it is easy to see how inconsistencies in measurement can result using this system. This system is not used by lens manufacturing laboratories or ophthalmic frame manufacturers.
The Box System
The box system is more accurate and more widely used in the optical industry today. In this system, an imaginary box is drawn around the area to be measured. The distance between opposite, parallel sides of the box determine the length of the distance being measured. These measurements are of the lens, not the frame. All measurements are made from tip-of-bevel to tip-of-bevel even if it’s nested deeply in the frame. This system yields accurate measurements even with unusual shapes.
Key Measurements in the Boxing System
The Boxing System utilizes several key measurements to define the dimensions of an eyeglass frame, including:
‘A’ Measurement (Eyesize)
The ‘A’ measurement, also known as the eyesize, represents the horizontal measurement of the box enclosing the lens area. This measurement is crucial in determining the overall width of the lens. Factors such as pupillary distance and face width should be considered alongside this measurement to ensure a proper fit and visual clarity.
‘B’ Measurement
The ‘B’ measurement refers to the vertical measurement of the box enclosing the lens area. This dimension is essential in determining the overall height of the lens. Factors such as optical center, segment height, face length, and cheek protrusion should be considered alongside this measurement to ensure a proper fit and visual clarity.
Distance Between Lenses (DBL) (Bridge Size)
The Distance Between Lenses, or DBL, is the shortest distance between the nasal edges of each lens. This measurement is commonly referred to as the Bridge Size and plays a vital role in the overall frame fit. Factors such as the patient’s nose width and nasal bridge should be considered alongside this measurement to ensure a proper fit and visual clarity.
Geometric Center Distance (GCD) (Frame PD/FPD)
The Geometric Center Distance, or GCD, represents the distance from the geometric center of one eyewire to the geometric center of the other. This measurement is also known as the Frame PD and is used to determine the optimal positioning of the lenses in relation to the wearer’s eyes to ensure optimal visual clarity.
Effective Diameter (ED)
The Effective Diameter is a measure of two times the longest radius of the lens shape. The most accurate way to measure ‘ED’ is to first mark the geometric center of the lens, where half the ‘A’ and half the ‘B’ meet. From that point, measure to the furthest tip of the bevel and multiply that length by two. This measurement is used in combination with decentration distance to determine the minimum lens blank size required to fit a specific frame.
Practical Applications of the Boxing System
The Boxing System’s comprehensive approach to eyeglass measurements has made it an indispensable tool in the optical industry. Opticians and eyewear specialists rely on this system to:
- Accurately select the appropriate frame size and lens dimensions for a customer’s specific needs.
- Ensure a comfortable and precise fit, minimizing the risk of vision distortion or discomfort.
- Facilitate effective communication and standardization between eyewear manufacturers, retailers, and consumers.
- Enable efficient ordering, manufacturing, and dispensing of custom-made or specialized eyewear.
The Boxing System’s Advantages
The Boxing System’s widespread adoption in the optical industry can be attributed to several key advantages:
- Accuracy: The use of an imaginary box around the lens shape, rather than relying on the lens edges themselves, helps to minimize inconsistencies and improve measurement precision.
- Versatility: The Boxing System can be applied to a wide range of frame shapes and sizes, from traditional rectangular designs to more complex and irregular shapes.
- Standardization: By providing a common language and framework for eyeglass measurements, the Boxing System facilitates seamless collaboration and communication across the industry.
- Adaptability: The system’s flexibility allows it to accommodate evolving eyewear trends and technological advancements, ensuring its continued relevance in the ever-changing optical landscape.
OTI Notes on Boxing System for Opticians
The Boxing System has played a pivotal role in shaping the optical industry’s approach to eyeglass measurements. By offering a standardized, accurate, and versatile framework, this system has become an essential tool for opticians, eyewear designers, and consumers alike. As the industry continues to evolve, the Boxing System’s enduring relevance and adaptability ensure its ongoing importance in delivering the perfect fit and visual experience for eyeglass wearers worldwide.
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