What is Vertex Distance? It might seem like an impossibly small measurement, but vertex distance is just one measurement we consider when crafting your progressive lens. It refers to the distance between your eye and the back of the lens. Lens power and magnification effects change when your lenses are further from your eyes, similar to how a magnifying glass enlarges an object the further away it is held.
Why We Measure: Every patient’s face is different and the vertex distance will change from person-to-person, even with the same pair of glasses. This is especially true for progressive lenses, which cater to complex vision requirements. The height of the window used for reading must also allow space for distance viewing and vice versa. If your frames are prone to slipping down the bridge of your nose, or sit at an awkward angle, your progressive lenses will not work as well.
When Do We Measure Vertex Distance? Vertex Distance is one of the only things we measure once every other part of the process is complete. After you have chosen your frames, we look at how much space we have for each prescription to fit in the frame. We then consider how far those frames will sit away from your eyes by measuring the Vertex Distance. Once the distance is determined, all the other aspects such as working distance, down gaze angle, near point inset and inter-pupillary distance fall into place.
So now you can see why a mere prescription on a piece of paper does not make a good pair of glasses. By guiding you through the stages of this process, we are sure that we’ll provide you with a pair of progressive lenses that feel as natural as possible. If you’re a bifocal wearer, or have complex vision requirements that you haven’t yet addressed, it’s time to make the easy switch to progressive lenses – just call Doig Optometry at 403-333-3353 or visit our Calgary location (102, 8180 MacLeod Trail South, T2H 2B8)