Ask the Labs
By Joseph L. Bruneni

SOMETHING NEW IN PROGRESSIVES

Q We had a salesperson call on us with a new progressive called Definity™ that has two progressive areas. This sounds like progressive "hype." Is there any sound logic to a two-sided progressive?

A The new progressive you ask about is only available in 20 percent of the country, but does represent a substantial design change from conventional progressives. All other progressives have progressive curves on one side of the lens (in most cases, it is the front surface). Gradually changing power in the progressive channel between distance and reading area requires pushing unwanted power changes to the sides of the channel, usually below the 180 degree line.

Lens manufacturers have different ways of positioning those distortion areas, but the distortion area is always on the same surface as the progressive curves. This new progressive uses a technology called "dual add™" that positions some progressive curves on the front and some on the back. The thinking is that the progressive curves are divided between front and back surfaces in a way that the peaks of peripheral distortion on each surface will offset one another.

The manufacturer claims the result is a wider intermediate zone with a smoother transition from distance to near. The lens is being marketed as a premium product.

RECOGNIZING COMPUTER LENSES

Q  What is the difference between those computer lenses called variable focus and conventional progressive lenses?

Also, how do you recommend we identify variable focus lenses when patients come in wearing lenses they purchased elsewhere?

A This is a timely question-- more variable focus lenses are being dispensed, so the chances of patients coming in with them are increasing. Replacing a variable focus lens with conventional reading lenses or a progressive could well generate an unfavorable patient response.

Variable focus computer lenses fall into the progressive category. They change power, but unlike progressives, most do not provide distance vision.

To identify variable focus lenses, look for a slight swaying motion in the bottom portion of the lens when looking through them at arm's length.

Additionally, they can be spotted by looking for engravings showing the horizontal location marks or a manufacturer's logo.

Which Setting for Pupilometers?

Q  In Ophthalmic Dispensing Guide, a dispensing manual we use in our office, a section explaining the use of a corneal reflection pupilometer (CRP) recommends setting the adjustable foci length dial of the instrument to 40cm. Since the dial offers a variety of settings, why should the 40cm setting be used rather than one of the others?

--Matthew del Valle, Vision One, Boise, Idaho

A  I wrote the dispensing book you refer to, so I should be able to answer the question. First, some background: All progressives use the same nasal inset of 2.5mm for the reading area of each lens. The 5mm difference between distance and near is an industry standard for progressives. Consequently, it doesn't matter whether the distance or near PD is submitted to the lab as long as the lab knows which PD was written on the prescription. I suggested using the near setting of 40cm in the manual because published literature with the most popular pupilometer recommends that setting. Pupilometers usually offer a variety of near settings for special needs, but 40cm is considered the most commonly used near distance.

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.