Ophthalmic Lens Measurements

Now let’s discuss some of the basic ophthalmic lens measurements that you need to understand prior to taking any other measurements for patient prescription. First, we have the A measurement. The A measurement on the lens is also referred to as the eye size, or the lens size itself. This is measured by removing the lens from the frame and measuring from the temple exterior edge of the lens to the nasal or interior edge of the lens itself. And is measured in millimeters. 

Next, we have the B measurement. The B measurement is the height of the lens. Measured from the lower edge of the lens or the deepest part of the lens bottom to the top or highest edge of the lens itself, also measured in millimeters.

We also have the ED measurement, which is the diagonal measurement that can be taken from the lower temple edge of the lens to the upper nasal edge of the lens, measured in millimeters. 

Finally, we have the lens circumference, which is exactly what it sounds like. We measure the entirety of the exterior edge of the lens, wrapped completely around the lens itself.