According to Vision Watch only 30% of ophthalmic lenses purchased in the U.S have anti-reflective coating whereas Canada and Japan for example over 90% of lenses are sold with anti-reflective coating. We think it is a major “optical crime” that 70% of American eyeglass wearers are dealing with unwanted glare and would like to encourage a change to make anti-reflective coating a standard rather than an option. For those practices that do their own edging getting really comfortable with edging AR coated lenses will help that happen.
With that thought in mind, here are some anti-reflective lens edging tips from a few of our sponsors:
Use specialized roughing cycles for polycarbonate to avoid slippage especially for Anti-Reflective coated polycarbonate lenses.
The best way to avoid slippage when edging hydrophobic or coated lenses – Finishing hydrophobic lenses is no longer a technical challenge with an edger that includes an automatic setting for processing coated lenses. On Briot edgers, this setting is called the “Slippery Mode” and it automatically adjusts machine speed and chuck pressure to avoid slippage. When edging any kind of coated lenses, make sure you select good quality leap pads. Clean the blocking surfaces to ensure a good bond, and use blocks that are in good condition; worn out blocks will lead to problems.
The key to edging hydrophobic-coated lenses is controlling the variables that lead to slippage. Follow this list of procedures that will collectively minimize slippage on hydrophobic and super-hydrophobic coated lenses. For maximum effectiveness be sure:
- Your roughing wheel is not worn
- You are using the largest blocks for the frame
- The blocks match the base curve of the lens
NOTE: On heavy minus lenses, edge the lens in two passes:
- Set the SIZE on the edger up 3mm on the first pass
- Unchuck and rechuck the lens
- Press R/L twice
- Set the SIZE on the edger back to 0 and re-edge the lens
All anti-reflective lenses should be handled with extra care.
- Use edging blocks that best match the front curve of the lens.
- The shape of front and backside chucks should be similar, minimizing flexing of the lens.
- If not using Blocking Pads specifically designed for hydrophobic coatings, apply an edging enhancement tape to both surfaces of the lens will help prevent slippage while protecting the lens surfaces.
- It is common to apply localized pressure to the block and pad to ensure good contact before edging, but this can cause excessive flexing of the lens.
- Ensure all edging wheels and cutter blades are clean and sharp. Follow manufacturer recommendations for cleaning/re-true/replacement.
- Ensure edger chuck pads are clean.
- Edger chuck pressure should be set to the least amount recommended by the manufacturer. Manual chucking requires experience.
- If possible, reduce the head pressure and “flow rate”. Check with your edger manufacturer.
- Edging down lenses using multiple cycles to avoid slippage is acceptable, but size lenses exactly- leaving lenses large will create unwanted stress on the lens.
- After edging, rinse lenses well in clean water and gently de-block lenses by twisting the block off. Do not flex or bend the lens while removing the block.
- Use light pressure when PIN beveling and while edge polishing.
- Use lens alignment pliers only if necessary, trying to avoid altogether