Q. Which Progressives Are "Hard?"
One of our patients has been wearing a pair of old AO Ultravue progressive lenses. The lenses are quite old, since Ultravue was one of the first progressive lenses on the market.

We need to find out which PAL is still available with a hard design so he can adapt to a new lens easily. He's quite happy with the Ultravue. Any thoughts?

A.
Generally, older progressive lens designs will be harder than newer designs. The advantages of a harder design are shorter corridors and wider near/distance zones. Keep in mind, however, that newer designs often provide wide zones and relatively short corridors without as much hardness as the older designs.

In any event, here are just a few harder designs that I believe are still currently available: SOLA Optical VIP, American Optical TruVision, Orcolite LineFree.

In addition to these, lenses like the SOLA Percepta, Varilux Comfort, Signet-Armorlite Kodak, and Rodenstock Life offer pretty wide zones and short corridors without quite as much hardness in many cases. There are several others, as well.--Darryl Meister, ABOM, SOLA Optical Technical Marketing.

Q. Poly Over Poly
I'm a licensed dispensing optician in Washington state. We use Bolle and other eyeglasses that feature a poly shield in front of holders for prescription inserts. I have heard that we should not put a poly insert behind another poly lens shield. I was told only a CR 39 or high index product should be used for the insert. Is this true, and why?

A.
The reason you heard concerns about using a polycarbonate lens combined with a polycarbonate shield is because of poly's lower Abbe value compared to regular plastic or glass. Although the lower Abbe value can result in more chromatic aberration than desirable, do not automatically rule out polycarbonate as your choice.

Lower Abbe was more of a problem back when labs and dispensers did not fully understand the properties of polycarbonate lenses. All aspects of manufacturing polycarbonate lenses have greatly improved (including injection molding, scratch resistant coatings, and aspheric designs). Follow the same precautions as with regular eyewear when deciding which lens material to use with frames featuring a polycarbonate shield. Take into consideration the intended use, prescription, decentration, insert size, and vertex distance when choosing the best lens material for the customer.

Follow these basic steps and you can successfully dispense CR 39, high index, or polycarbonate with this specialized type of frame.--Jack Ichinaga, America Sport Optical, Torrance, Calif.

Q. Hazards of Polycarbonate Dust
What health risks are there if the fine particle dust of polycarbonate lenses (during the edge-down process) are inhaled on a long-term basis? On a short-term basis? To pregnant women? And also, what proper ventilation is required for this type of manufacturing? The dust is like powder and is airborne and on the surfaces of things regularly touched.

A.
The following comments are from our Health, Environmental, and Safety Department: Polycarbonate dust is considered a general nuisance dust and is not more hazardous than general particulate dust that typically floats in the air. In fact, polycarbonate dust is less toxic and less irritating than talc dust used as body powders.

Like conventional dust particles, high levels of polycarbonate dust can cause general skin irritation by plugging of skin pores. The maximum amount of general dust particles permitted in air by OSHA is 15mg/m3. This level should also be observed for polycarbonate dust.--Robert Pyles, Bayer Corporation EB

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