troubleshooting tips

Ways to Work High Index

by Karlen McLean, ABOC, NCLC

High index lenses can be challenging to work. From measuring and fitting to cutting and edging, high index materials have their own set of rules. Keith Cross, RDO, senior director of Rx technologies with Younger Optics, offers key ways to work the quirks of high index.

KNOW PD AND DECENTRATION

1 Let the lab know if you will be vertically decentering the lens. When working with aspheric lenses, keep decentration to a minimum. Labs can't grind in decentration; the lens design is based on center. Try to keep the vertical center within 3mm of the optical center.

CLARIFY TINT AND DENSITY

2 A non-tintable coated lens can be ruined during the tinting process. It's best to send a tint sample to the lab to help avoid confusion or delays. When tinting high index lenses, keep the vat temperature at about 175°, which will help avoid lens streaking or coating blotching. Check lenses every 10 minutes; remove the lens from the tint, thoroughly rinse, and check for tint color consistency and defects.

SHARE THE DETAILS

3 Provide exact frame measurements and frame model details. This includes A, B, DBL, and ED measurements.

This optimizes the use of the high index lens material, giving the ECP the thinnest possible lens. Also, let the lab know if the lens will be grooved, drilled, or will have other mounting arrangements.

ORDER AR UP FRONT

4 Many newer advanced coatings can only be done on uncut lenses. Edging the lenses and then sending them out for AR cannot always be done.

If this is your preference, be sure to check to see if this method is compatible with the type of AR you're requesting. Most labs supply ECPs with special leap pads and/or front surface tape for super-hydrophobic lenses that are being edged at the practice.

UNDERSTAND YOUR EDGER

5 Most newer edgers have specific settings for different materials and coatings. Understand which setting is the most appropriate based on your material and coating.

Certain AR coatings have minimum center thickness (CT) requirements on low power Rx's to avoid flexing and crazing of the coating during the edging process.

BE AWARE OF WHAT'S POSSIBLE

6 Processing a 1.67 index lens -1.50 sph. with a 1.0mm CT will probably cause breakage. Most labs have policies that from plano to -2.50 sph., lenses are processed with a 1.8 to 1.5mm CT, gradually descending based on Rx.

Understanding these details will help ensure that the final result lens is just what the doctor ordered. EB