How many reading this are promoting and selling Free-form progressives? Come on, put up your hands and keep them up.

Good, now keep your hands up if you are also promoting and selling dual aspheric and Free-form single vision. Just as I thought, not enough of you have realized the opportunity and benefits of these powerful Free-form based single vision lens technologies. For those with your hands up, congratulations for recognizing the advantage of these lenses.

Oh, you can put your hands down now.

THE SINGLE VISION OPPORTUNITY
It's time to consider changing the way we think of single vision and shift even the basic SV order to one that includes more technology in the way that the lens surfaces are designed. That means the regular use of aspheric, atoric (Dual aspheric) and Free-form surfaces.
Technology Beckons.

Asphericity, dual asphericity, atoricity and Free-form are better choices for a clearer field of vision. Each provides an improvement in the way that a patient sees. Asphericity has been typically used to change the cosmetic form of plus lenses so that the wearer gets a flatter lens and reduced magnification. All this while retaining the optics of the steeper 'best form' or 'corrected curve' lens that previously would have been used. Patients are thrilled when a 4 base lens rather than an 8 base lens is used to make that +3.00 prescription, especially in a 1.67 or 1.74 index material (Fig 1). Why?

First, technology of material (1.67 and 1.74 high index) provides a thinner lens form. Then, reducing the front surface bulge of a +8 base to that of a +4 with the accompanied aspheric correction in the periphery of the lens makes the lens thinner and better looking, yet delivers reduced magnification and off center clarity comparable to its steeper form. That's merchandisable.

Now take two-steps forward, but pause to use each step separately when the right circumstances present (Fig. 2). First, recognize that aspheric lenses are only a partial design solution. The lens' front surface is a rotational asphere i.e., has the same amount of asphericity in all directions. As a result, the amount of asphericity can only correct for one lens power, typically the sphere power. That's okay if the prescription is a sphere or a cylinder of 0.75D or less.

However, if the cylinder is 1.00D or more; the asphericity is not correct for the cylinder meridian. For example, SEIKO double aspheric lenses solve the problem by using the aspheric lens front, and then cutting a Free-form back so there is a different aspheric correction applied to each meridian of power. There are two ways to do this, either atoricity (spherical front/Free-form back) or double asphericity (aspheric front, Free-form back). Both are created using a Free-formed back lens surface.

Mark Mattison-Shupnick, ABOM, is currently director of education for Jobson Medical Information LLC, has more than 40 years of experience as an optician, was senior staff member of SOLA International and is a frequent lecturer and trainer.