Fix and Fit
Keeping those lenses in the frame
By Alex Yoho, ABOM

Ever have an un-bespectacled client come into your dispensary with a deer-in-the-headlights look in their eyes? This usually means they have had a lens come out of the frame, which is probably as traumatic as sitting on their eyewear. The problem is, this time it's your fault. They were just sitting there and, "all of a sudden it just fell into my lap!" Sometimes it's worse, they were walking to their car and the lens fell out, landing on the sidewalk, and broke into a million pieces.

Measure lenses with the plus side up. It is less likely to slant as tension is applied that way

Whatever the reason, you're on the wrong side of a bad story. It really is our fault. Let's take a look at some of the reasons lenses fall out of frames.

As dispensers it's our responsibility to give the lab all the information we can. If you are using the latest technology and sending your orders via a remote tracing device, you're off to a good start. Be sure that your tracer is calibrated daily and don't assume it's going to be flawless. Check the circumference to be sure the tracer is sending good information.

You can check with a circumference tape with reasonable accuracy, which for those without tracers, may be the only way to obtain this information for the lab. Always note the circumference you find on the patient's permanent record. There's no such thing as information overload when it comes to fitting a lens to a frame. Some people have difficulty taking a circumference measurement, but there are ways to improve consistency.

It's probably best to measure the lens with the plus side up. It is less likely to slant as tension is applied that way. Proper tensioning is another area for trouble. You should obtain a standard gauge from your lab to be sure your reading matches theirs. This could be as simple as a lens with a known circumference or a pattern cut to an exact size. Some C-sizers come with their own calibration disc. The goal is to determine how hard you need to pull the tape to get the marked reading.

	Trust your lab's measurements, as its equipment is thoroughly calibrated to ensure correct work

Medium tension should close up all gaps between the tape and lens without stretching the tape or causing it to tear. Always use the cover that comes with the unit to ride the top of the tape, ensuring that it doesn't lean over the lens as you tighten. You should change the tape as frequently as needed and have a spare, or two, on hand at all times.

If for some reason your measurements and the lab's do not agree, you can improve the communication by measuring a dozen or so lenses. Then compare your measurements to the lab's to determine the average discrepancy. If your readings are .5mm larger than the lab's, then reduce your measurement by .5mm when you order lenses.

It is critical to swallow our pride and adapt to the lab as the standard. We can count on the labs to ensure that their equipment is thoroughly calibrated since one edger out of calibration could mean thousands of dollars in spoilage. Most labs keep tolerances of one tenth of a millimeter on circumference by using electronic circumference devices. It usually takes more than .25mm to make a noticeable difference in lens fit.

You can remove the lens and carefully trace around it if you don't have a remote tracing device. Things to watch for when tracing a lens by hand are:

Establish the 180 axis of the lens shape. Put a straight line on a piece of paper and match a bifocal line, three lensometer dots, or two progressive ID marks, to the line. You'll have to put the lensometer dots on with the lens in the frame and the frame resting with both eyewires resting on the lensometer's table.

Carefully trace the lens shape with the pen or pencil in an exact upright position. Don't be concerned that the drawing is larger than the lens; your circumference measurement will take care of the size.

Mount the lens correctly. When a plastic frame is heated and the lens is inserted, there is a tendency for the eyewire to roll its inside groove outward. This can allow lenses to pop out easily, giving the appearance that they were made too small. In reality, they may have been too large, causing the eyewire to roll. To avoid this problem, mount the lens from the front, starting with the temporal edge. Push the nasal edge with your thumbs while pulling the eyewire up and around the lens until it pops in at the nasal corner.

If the eyewire has been rolled from someone else's mounting, you can heat the area and roll it back a bit more than needed. This "over-rolling" of the eyewire will come back to normal as you mount the lens properly. If, after unrolling the eyewire, you find the lens too large, you should have the lens cut down to fit. It will also help when reducing the size to make the bevel a bit sharper, giving the lens extra bite.

It is also possible to roll the eyewire on a metal frame, usually when the eyewire is curved with forming pliers to follow the bevel of the lens. In this case, you can use any pliers with nylon jaws on both sides, and roll it back into place, trying to keep the contour of the bevel. If the lens is highly curved, it helps if the lab edges it with a bevel curve that is flatter than the base curve of the lens. The more curve a frame has, the more likely it will pop off.

This is true of frames with straight tops. When these frames are curved to match curved lenses, the top seems to hinge at the corners, allowing the lens to pop out at the top, particularly when the frame is fit with lots of head tension.

In the next Fit & Fit, we'll discuss methods of fitting small lenses.