HANDS ON - FIX AND FIT
Ordering Lenses That Will Fit
by Alex Yoho, ABOM

One of the most frustrating things in this life is getting a new pair of lenses for a patient's old frame and finding that they don't fit.

The computer adage, "garbage in, garbage out" is perhaps the best description of the relationship between new lenses and an old frame. Our responsibility as opticians to correctly send the order into the lab is paramount to a successful fit.

Let's look at some of the things that will make a difference.

	(From top to bottom) To send an accurate trace to the lab, use dots established by a lensometer or a straight seg line to match to the 180 line. Draw a line around the lens. Mark the lens R or L and indicate the nasal edge

NEW LENS TWO-STEP

Getting around circumference. The best piece of information you can give your lab is the circumference. But first, you must check your circumference device—have your lab make a round lens or pattern that is a specific circumference.

Compare the circumference that you get on your circumference measure to the circumference that the lab gets. If there is a difference between the two readings, adjust your gauge or replace the tape that is used and see if that corrects the difference.

If it does not correct the difference, compensate the circumference on each order. For example, if the lab standard is 170mm and your reading is 170.5mm, you will need to reduce the circumference that you order by .5mm each time.

You may also find in time that the circumference can be exact, but the lens does not fit perfectly. This can happen because the angle of the bevel on the lens does not match the angle of the groove in the frame. Normally, bevels are fairly consistent from the lab, so in time, you will get a feel for fine tuning the fit.

Stay in shape. Shape is also critical for a good fit. Usually, the best way to get the shape to the lab is to use a digital tracer and send the shape electronically to the lab. But tracers are fairly expensive, and you may use an alternative method.

Most labs offer tracing cards to draw the shape on, or you can just use a piece of paper with a straight line drawn on it (see photos on previous page). This line will be used to ensure that the lenses are on axis and that bifocals will be straight.

The next step is to establish a 180 reference on the lenses. If there is a bifocal or trifocal line, you may just use that, placing the lens back-side down and lining the bifocal line with the line on the paper and tracing around the lens.

If it is a single vision lens, place the eyewear in your lensometer and spot the lens with the inker, taking care that all three dots are made on the lenses. Then remove the lens from the frame and use the dots instead of a bifocal line to ensure the lens shape is straight. Also indicate where the nasal corner is on the drawing so the lab will know if it is a right or left.

When you draw around the lens shape, try to keep your pen perpendicular to the frame. This will give you a more accurate drawing than trying to keep the tip of the pen tilted in toward the lens. Try to make the drawing one thin, smooth, continuous line. The drawing can be larger than the lens since you will be sending a circumference as well.

If you are tracing a sample lens from a new frame, be sure there are no gaps between the lens and the frame before removing them. Though there are times when you should send a frame (such as wrap frames), following these instructions should give the lab all the information it needs to make your lens-only job a perfect fit every time.

Questions or comments may be E-mailed to the author at ayoho@cox.net