Offer Added Value With
In-Office RGP Modification

BY EDWARD S. BENNETT, O.D., M.S. Ed.
OCT. 1996

Being able to verify and modify RGP lenses in your office will differentiate you as an RGP expert. Having these capabilities is economical and efficient, enhances your confidence and ultimately results in more satisfied patients.

HANDS-ON TRAINING

There are numerous modification workshops available nationwide for hands-on training. The Contact Lens Manufacturers' Association (CLMA) member laboratories and the RGP Lens Institute (RGPLI) often sponsor such events. The RGPLI also offers a video on how to verify and modify RGPs.

BASIC EQUIPMENT

Modification equipment is available in economical packages ranging from basic ($225 to $350) to deluxe ($300 to $500). The basic package usually includes a single-speed modification unit as well as sponge and/or velveteen tools for edge and surface polishing, suction cups and polish. Consider investing in a variable-speed unit because the lower spindle speeds minimize optical compromise during modification.

A deluxe package usually includes brass or diamond impregnated radius tools for blending and flattening peripheral curves, a spinner (suction cup type is best) for repowering and polishing, an anterior bevel cone tool (90º tool is recommended) for thinning the edge, and either a 7x loupe or a gauge for measuring diameter. Some labs include the spinner or a limited number of brass radius tools in their basic package.

Verifying the lens edge is the most critical aspect of rigid lens inspection. A spinner-based edge inspection device ($200) or a projection-based device ($600) is a valuable addition to your RGP modification toolbox. [Editor's note: See page 20 for Dr. Bennett's list of CLMA member labs that sell modification equipment.]

MODIFICATION PROCEDURES

The most frequently indicated procedures are front surface, back surface and edge polishing, repowering, and blending/flattening peripheral curves. In a recent study, Bruce Morgan, Vinita Henry and I found all of these procedures to be successful. The only exception was using a velveteen pad tool to add power to a high Dk material with a high (1600 RPM) spindle speed unit; this reduced optical quality. I also don't recommend reducing diameter as this may cause optical compromise.

Some pearls to remember: use a lower spindle speed when modifying high DK materials; apply polish frequently to minimize heat buildup; apply minimal pressure. CLS

Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis; he is executive director of the RGP Lens Institute.