fix and fit

Spectacle Lens Measurement Tips

by Alex Yoho, ABOM

Curtailing dispensing problems is a major practice concern. Being confident that you are well prepared when a patient comes to you for eyewear will make everything go smoothly on both sides of the dispensing table. Be certain that you are coordinated with the lab during the entire lens production process.

LENS-ONLY JOBS

Provide the lab with an accurate circumference. Ask your lab to send you a round lens with the circumference that they find. It's great when your circumference tape is on the money, but everyone's measurements are a little different. By using the standard lens provided by your lab, you can see if you need to compensate your measurements for the lab.

If the lab sends you a standard lens that measures 170mm, but you get 169.5, you'll have to add .5mm to each order you send to the lab. Such details require daily attention.

LENS THICKNESS

Know what works and what doesn't. One of the toughest mistakes that dispensers make is not considering the form that the Rx will take.

Example 1: Just knowing that a plus lens is thicker in the center than the edge, and that a minus lens is thicker on the edge than the center, seems to be ignored.

Example 2: Some ECPs design a +6.00 in a narrow rectangle and wonder why it is so thick on the top and bottom. We need to think it through and understand that the narrow shape will cut deep into the thick part of the lens.

CURVATURE

A plus lens is more curved than the flatter form of a minus lens and when it deviates from the standard curve of the frame, the result can be a lens that fits poorly in a frame and pops out easily.

Consider rediscovering the seemingly lost art of curving an eyewire to better accommodate a lens.

POWER AND PD

Of course the stronger the power, the thicker the lens—and the larger the lens, the thicker it gets.

In the case of a narrow PD, don't ignore the fact that a narrow PD (compared to the frame) necessitates a larger lens to decenter the optical center to match the PD and causes thick edges in the nasal or temporal side.

LENSMETER

Be sure to focus that lensmeter. You would be amazed at the number of lenses dispensers send back to the lab for power, only to be told that they are indeed on power after all. This is often due to the neglect of dispensers to focus the lensmeter for their own vision.

ECPs need to:
1) Learn the proper technique of eyepiece focusing.
2) Utilize the techniques before every inspection.
3) Understand the tolerances that ANSI allows. This could save many needless delays.

Paying attention to these basic details can make a difference in your practice and how it is perceived. EB