Techniques for Fitting Eyeglasses

"Fitting" eyeglasses is a term used by eye care professionals to describe measuring and adjusting frames and lenses. The three main techniques for glasses are sizing the frame, adjusting the frame and measuring for the lenses. Opticians use all three techniques to make sure you get the best possible vision and fit from your glasses.

Fitting the Frame

• An eyeglass frame should be comfortable as well as stylish. Most people will choose comfort over looks, but it's possible to have both if you spend time trying on frames and finding one that looks and feels right. A frame should be wide enough across the front and fit so the temples, or "arms" do not press into the side of the head; and the temples should be long enough to extend over the curve of the ear.

  Frame size varies with style and trends. Ideally, your eyes should be centered in each lens, about in the middle horizontally and vertically. The frame should balance with your face, not too large or too small.

Adjusting a Frame to Fit

• Opticians use a standard alignment or standard adjustment procedure for all frames before dispensing a pair of glasses to a patient. A standard adjustment includes tightening any screws on the frame. The lenses must be parallel, called co-planar alignment. The optician also checks that neither lens is more forward than the other. The bridge, the part of the frame that sits on the nose, must not be skewed. Looking from the top down, the frame should be in a slightly curved line that follows the front of the face. If the frame or bridge is twisted, the frame should be adjusted and re-aligned.

  Metal frames are adjusted with special pliers. Plastic frames are heated in a special heating pan or by a machine that blows warm air over the frame to make it more pliable.

Measuring Techniques for Eyeglasses

• The prescription part of your lens is placed in a specific location in front of your eye. Opticians measure how far apart your eyes are, called a PD for "pupillary distance", and communicate this number to the lab that makes your lenses. If you wear bifocals, other measurements are used as well. The bifocal height tells the lab where to place the bifocal in relation to where your pupil is located in your frame. Most people are not symmetrical and the bifocal height may be different for each eye. Other measurements may also be used, depending on the complexity of the prescription and the material of the lens.

Final Adjustments

• After you try on glasses, final "tweaks" are done to make sure the frames and lenses fit correctly. The frame should rest comfortably on the nose. The glasses should not slide down or feel too tight. The temples should follow the curve at the back of the ears and not press into the mastoid, a very sensitive area of the skull behind the ear.

  New glasses fit like new shoes and sometimes stretch out a bit, especially at first. Several adjustments may be necessary after a few days or weeks of wearing a new frame. Have your glasses adjusted regularly to maintain proper fit and comfort.