Education Center
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The Boxing System
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What is A, B, ED?
A - The horizontal distance between the furthest temporal and nasal edges of the lens shape. The A measurement is also commonly known as the eyesize.
B - The vertical distance between the furthest top and bottom edges of the lens shape or the distance between the horizontal sides of the box.
Effective Diameter "ED" - Twice the distance from the geometric center of the lens furthest edge of the lens shape. The ED can also be defined as the smallest diameter lens that would cutout, if the frame's geometric center matched the lenses optical center. ED is used in combination with decentration distance to select the minimum lens blank size required to fit a given frame.
These measurements are crucial when ordering uncuts! Correct measurements will not only allow enough lens to cut out, but also allows the free form design to take into account the final lens shape during calculation.
Outline of a Progressive
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Need help measuring your progressive lens on the lensometer? Check out the diagram below!
Transitions- more than just Grey and Brown!
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Transitions VII- Standard Transitions are available in Grey, Brown and Graphite Green. These lenses are the traditional Transitions that go from clear to dark when exposed to UV light.
Transitions XtraActive- XtraActive Transitions are available in Grey and Brown and carry a level one tint when deactivated. These Transitions get darker than traditional when activated and even activate somewhat behind a windshield.
Transitions Vantage- Transitions Vantage is the polarized option from Transitions. These lenses also carry a tint behind the windshield.
Conventional lenses have a front surface that is spherical, meaning it has the same curve across its entire surface, much like a baseball.
Aspheric lenses, on the other hand, have a more complex front surface that gradually changes in curvature from the center of the lens out to the edge.
On plus lenses, Aspheric lenses cause less lens to bulge out on the center. This causes the lens to be thinner, lighter, and cause less distortion.
When looking at a grid with aspheric lenses, the grid is in focus across the lens versus being magnified only in the center with distortion toward the edges.
The linear distance between the beginning of the power gradient—the Fitting Point—and the target add value, most commonly defined as 85 percent of add power, is called the corridor. The Signature comes in multiple corridor lengths; which length is used depends on the seg height and Rx. Most of the time, the corridor used will be 2-3mm less than the seg height. Thus, a Signature with a seg height of 18mm will have a corridor of 16mm. This means that the patient's eye has to travel 6-8 degrees to go from the optimal reading zone, to the optimal distance zone.
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