I always get a sinking feeling when I see someone wearing a pair of improperly adjusted eyeglasses. I get that feeling because the poor adjustment I see means that somewhere an optician has been trained improperly and is making the same mistake on a daily basis.
The most common error I see is temples that are fitted too closely to the patient's head. This has two consequences. First, it will create a deep indentation in the side of the patient's head that not only can be clearly seen but felt. Often the indentation is so deep that it is clearly visible after the patient takes off the glasses.
Second, the inward pressure of the temples against the side of the head will make the glasses tend to slide forward. This will cause the patient to push the glasses constantly up each time they creep down his or her nose.
The fitting triangle
One of the keys to learning to fit eyeglasses properly is to understand the fitting triangle. This concept is described brilliantly by Russell Stimson in his book.1
In the chapter entitled "The Fitting Triangle," Stimson noted that the first point of contact for a temple needs to be at the top of the ear. The temple tip then is adjusted behind the ear. Fitting the temples in this way will cause the temple tips, not the temple, to grip the head in such a way that the glasses will be pulled gently backward. Therefore, as a result of the physics involved, the eyeglasses will want to creep up the patient's nose, not down. Conversely, should the first point of contact be in front of the ear, the temples will press constantly into the side of the head, forcing the glasses forward.
The availability of frames with spring hinges seems to have made matters worse. Inexperienced and ill-trained opticians rely on spring hinges to hold poorly fitted eyeglasses in place. The springs only work, however, when the frame is adjusted tightly enough for them to flex. This increases the inward pressure of the temples against the head. When these temples are adjusted incorrectly, the springs will squeeze the glasses forward forcefully and continuously.