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Article Date: 12/1/2003

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GP insights
What's New in GP Lens Manufacturing?
BY LORETTA B. SZCZOTKA, OD, MS, FAAO

In the last decade, not only have GP lens polymers improved in oxygen transmission and stability characteristics, but experts have also refined and fine-tuned the GP manufacturing process. They were able to perfect this process thanks to improvements in lathes and tooling.

To prove this point, Carl Moore, FCLSA, of Con-Cise Laboratories, shares his wisdom.

Good News

Says Mr. Moore, "Computer-guided lathes can cut surfaces more precisely and with greater accuracy than the lathes of the 1980s. For you and your patients, this means that the duplication of one lens to another is repeatable and predictable. Lathes store database files for patient-specific lenses, and you can then retrieve those files, scan and download them each time you require a remake."

A Push for Less Polishing

Mr. Moore also stressed that tooling has improved. Labs can now cut GP contact lenses with better diamond tool technology, which means less polishing time. Years ago polishing took up to three minutes or more to remove tooling marks, which could heat up plastic and dramatically alter the surface, stability and curvatures of the lens.

Today, polishing usually takes less than 15 or 20 seconds and requires only light pressure and soft sponge materials. Therefore, the parameters cut by the lathe are exactly what the final lens parameters will be, with less chance of curvature changes or warpage after the lens has been cut. Today's high DK and better wetting materials would have been difficult to manufacture in the past. On today's lathes they are done routinely.

Lathing's Latest Advances

Generating peripheral systems that are precise and accurate is also a benefit of modern lathing and tooling technology. In addition, some manufacturers can "blend" the curves during the lathing process with sophisticated design and cutting programs, therefore requiring less polishing. Again, the lower polishing time improves repeatability.

Lastly, the new manufacturing equipment can accurately duplicate the desired edge designs and edge thickness profiles from software programs. This means less hand shaping and polishing, which means better comfort and more precise variances in design to achieve lens movement and centration.

Are We Guaranteed Perfection?

Not necessarily, says Mr. Moore. It is still incumbent upon our labs and our technicians to calibrate the machinery and keep the tooling fresh and up to par to provide the highest quality GP contact lenses. Those lenses will have crystal optics; they will be free of surface defects and will maintain their dimensional stability.

What can you expect during your verification process? Practitioners may measure some minor differences in GP lens curvatures, particularly in higher minus powers, from what was ordered because of hydration and normal material dynamics, however those changes should not affect the expected performance of the lens on the eye.

Dr. Szczotka is an associate professor at Case Western Reserve University Dept. of Ophthalmology and Director of the Contact Lens Service at University Hospitals of Cleveland.

 


Contact Lens Spectrum, Issue: December 2003

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