Ask The Labs
?&A

WHY CAST LENSES?
Q I have several optometrist friends who lost money trying to cast lenses in their practice. In-office casting was dying out but now seems to be coming back to life. What advantages does lens casting offer to a retail office?

A Lens casting has gone through some ups and downs since the first retail casting units were introduced. The initial units were relatively crude and over time, lens casting by retailers seemed to lose its appeal. In recent years, however, there have been substantial improvements in the technology.

Traditionally, lens casting provides two advantages to retail offices:

1) The ability for same-day delivery of multifocals (bifocals and progressives).

2) A less expensive way to produce lenses (primarily progressives).

Several recent developments are brightening the future for lens casting. The first was the development of photo-chromic resins, making it possible to inexpensively produce an additional premium lens. The parameters of what can be cast continue to expand. It's now possible to cast aspheric lenses, further expanding the field of cast lenses.

Some believe the greatest potential will come as wholesale laboratories take up high production lens casting. Some large retail laboratories are now routinely casting lenses (primarily progressives and photochromics).

One casting equipment manufacturer recently announced it would be supplying Corning's SunSensor® resin--enabling labs to cast brand- name photochromic lenses.

In addition, a multi-branch lab organization is currently casting a brand- name progressive in some of its labs.

INSIDE-OUT LENSES
Q Could you explain what the advantages are of the new progressive addition lenses that have progressive curves on the backside of the lens instead of on the usual front side?

A These are available from more than one manufacturer. There are a number of advantages to positioning progressive curves on the inside of the lens. Magnified size differences created by various parts of the lens are reduced because the front surface is now spherical. Moving the progressive surface closer to the eye also reduces skew distortion so patients experience less swaying and swimming experienced by first-time wearers.

Most significantly, placing progressive curves on the back significantly expands the visual fields (for all distances). For cylinder corrections, back curves are atoric, aspherized to the patient's exact correction. Currently, these lenses are manufactured in factory labs, but several companies are now producing free-form equipment that will enable labs to produce these customized progressives locally.

Radio Shack to the Rescue?

Q We have a patient who tells us that Radio Shack sells kits to minimize the scratches in the polycarbonate surfaces of CDs and DVDs. The scratch is rubbed with the paste and then left to dry out. His family is going through some tough financial times and we'd like to help him if this would work. What's the official word on removing scratches this way?

A Like so many other things in life, this solution is too good to be true--for two reasons. To effectively remove scratches, the compound must have abrasive material in with the polishing agent. The major drawback to using this on polycarbonate lenses (or any ophthalmic lens) is that the rubbing and polishing will distort, if not destroy, the optics in that area. In addition, polycarbonate is a soft material, and polishing out the scratch will also remove the scratch coating. As a result, he can expect even more scratches in the future. But since the lenses are already ruined, there's no harm in trying.

If you have a question you'd like to have answered in Ask the Labs, send it to Joseph L. Bruneni. Fax: 310-533-8165. Phone: 310-533-4975. E-mail: joe@bruneni.com. Or mail questions to: Vision Consultants, 2908 Oregon Court, #I-2, Torrance, CA 90503. An archive of past Ask the Labs columns can be found on the Eyecare Business Website at www.eyecarebiz.com.