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Lens decentration is a standard and necessary step in the making of almost every pair of eyeglasses. It is the process of shifting the optical center of the lens so that it is placed directly in front of the center of your pupil. It is not a lens flaw, but rather a careful customization that ensures your glasses will give you the clearest and most comfortable vision.
read more about lens decentration ...Every lens has an optical center, which is the one spot on the lens with the purest vision. For your glasses to work correctly, this sweet spot must be lined up with your pupil. However, the geometric center of a frame is usually not in the same place as your pupil. An optician measures your pupillary distance (PD) to know exactly where the optical centers need to be placed. The lab then "decenters" the lenses to match that measurement.
Looking through any part of a lens other than its optical center can create a prism effect, which can make you feel dizzy or give you a headache. It can also cause eye strain because your eyes have to work harder to see. Proper lens decentration eliminates this unwanted prism. It ensures that when you look straight ahead, you are looking through the clearest part of the lens, which gives you the best optical accuracy.
To make your glasses, an optician takes
To make your glasses, an optician takes precise measurements of your pupillary distance (PD) and the height of your pupil in the frame. These numbers are sent to the lab. The lab starts with a large, uncut lens and shifts it so the optical center lines up with your measurements. Only then is the lens cut to fit the shape of your frame.
There is a physical limit to how much a lens can be decentered. Lenses are manufactured as round discs called "blanks." If a frame is very wide and your eyes are close together, the lens would need to be shifted so far inward that the outer edge of the frame might hang off the edge of the lens blank. Opticians calculate the "Minimum Blank Size" (MBS) to ensure the lens is large enough to cover the frame even after the necessary decentration.
No, it is a very important and positive step. It is a sign of a carefully made pair of glasses that has been customized for your eyes and your specific frame.
If the optical centers are not lined up with your pupils, your glasses can cause eye strain, headaches, and blurry or distorted vision. If a new pair of glasses feels "off," you should have them checked by your optician.
Yes, an accurate PD measurement is absolutely necessary for correct lens decentration. It is the main measurement that tells the lab how far to shift the optical centers.
The measurements needed for accurate lens decentration should be taken by a trained optician. This is especially important for people with strong prescriptions or those who wear progressive lenses. If you get new glasses and they cause you any discomfort, go back to your optician right away so they can check the alignment.
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