There is an element of physics when it comes to matching a frame to the patient’s head, with the forces of weight and friction playing a big part in overall comfort and fit, writes LEIGH ROBINSON.
The initial fitting and comfort of a pair of spectacle frames is often the lasting impression the patient has of the practice that you represent. If the frame is not chosen with skill and thought, the comfort and appearance will be affected. As well, there is a risk that the optical performance of the lenses will be compromised.
My friend Murray O’Brien, in his insightful dispensing article in the October issue of Insight, said: “The dispenser must be fully aware of the patient’s prescription before becoming too involved in looking at frames.” He is correct – prescription interpretation is another complete skill-set on its own, not for the faint hearted. A competent dispenser must be able to visualise where the thickness will be on any prescription and select frames accordingly.
With higher powered prescriptions, progressive powered lenses and freeform digital lenses in a market where the customer knows very little about their glasses, the dispenser must manage the fitting and adjustment of the frame. They should also assist the customer with the utility of their new spectacles, managing their expectations of their new lenses is essential for encouraging patient loyalty.
The purpose of a spectacle frame is to position spectacle lenses in direct relation to the wearer’s eyes. A spectacle frame is also required to enhance personal looks, to be comfortable and remain so. It should look good, look fashionable and be a good fit. But it must be fit for the intended purpose, and that is, to hold lenses in the correct position in direct relationship to the visual axis of the wearer.
Time taken with correct frame selection and adjustment will be important for the long-term wearing pleasure for the patient and care taken at this time will save time and angst later.
Fitting spectacle frames might seem an easy thing to do. Something that many people and practice owners think requires little or no training. Just put them on the customer, decide what colour they like and send it to the lab. But there are some elementary understandings derived from physics when it comes to matching a frame to a head. We must consider how the forces of weight and friction act upon a spectacle frame when it is being worn. When considering frame selection, these reaction forces play a big part in comfort and fit.
Most of the weight of the frame and lenses can be considered to act on the bearing surface of the bridge of the nose, so try to have as much of the frame as possible in contact with the face, across the bridge.
It’s at this stage of frame selection that we must get the frame fitting correctly. Once you have looked at the nose, it’s time to assess the temples. The temples should leave the frame front and pass the side of the head and only touch the head after the ear point. Spectacle frames should touch the patient’s face in three places only, at the nose and the two sides of the head, behind the ear. This is known as the fitting triangle.
Counteraction forces create forward motion of the frame-front at the bridge – this is counterbalanced by the temples. In effect the frame presses on the head and the head presses back equally.
The counteraction force behind each ear, has a backwards force component which counters the forward components of each temple at the ear, keeping the frame in position. Sufficient pressure is needed to apply slight grip to the side of the head. Too much pressure and it will create sore spots for the wearer.
At this point the frame’s temple drop should not touch the back of the ear for the same reasons, aggravation. A spectacle frame should NOT touch the ear at all, it must touch the sides of the head only. Now, the tricky part is that too much pressure on the side of the head (behind the ear remember) will create aggravation on the head but also on the nose.
The force from the head behind the ear, caused by overtight temples can also cause increased pressure on the nose, forcing the frame upwards and forwards. When a patient complains of a sore nose from their spectacles, we must adjust the frame completely. As well as checking the bridge fitting, you must also check the fitting of the temples.
ABOUT THE AUTHOR: Leigh Robinson is a teacher of Cert IV in Optical dispensing at RMIT University Melbourne. He also works as an optical dispenser at Mentone Optical in Victoria.
