What is Free-form?

Digital Surfacing, Free-form, Direct Surfacing

Digital Surfacing, Free-form, Direct Surfacing: It seems everyone has a different name for what amounts to the same process. They all simply refer to a more accurate method of creating a lens surface. Instead of conventional surfacing where a fixed curve lathe is used to create a simple surface, Free-form generators use a diamond-tipped point that can create any complex surface. The Free-form generator is so accurate that it only requires a small amount of polishing to then complete the optical surface, this ensures that the integrity of the lens design is maintained through the whole process.


The question now becomes what can you do with this higher degree of accuracy?

Adjustable Corridor Lengths: With conventional progressives the design is already molded on to the front of the lens. Free-form allows the lens design to be created specifically for a patient and their frame, so the concept of long and short corridor designs can be taken away. Now the corridor will be adjusted based on nearly any fitting height you request. (keep in mind you can also request a shorter corridor regardless of the height to tweak the design for a patient’s history.)

Correction for oblique astigmatism: As eyes rotate away from the optical center in a lens, the patient will experience cylinder in the periphery. By using advanced computer modeling at every angle away from the optical center, an advanced Free-form surface can correct for that cylinder. This can create perfect vision from edge to edge, especially in the distance area of the progressive. This is the primary benefit of Free-form SV, effectively making the whole lens the sweet spot.

Position-of-wear Compensation:  Free-form lenses also allow for the correction of additional parameters. POW compensation refers to the creation of an adjusted Rx that corrects for the discrepancy between the angle and position of the lenses in a phoropter and the lenses in the patient’s eyeglasses. The specific measurements are Panoramic Angle, Pantoscopic Tilt and Vertex Distance.


Base Curve Flexibility: By incorporating computer modeling and POW compensations, Free-from also allows you to move away from best curve fitting without sacrificing peripheral optics. Traditionally the front curve of a lens was chosen based on an attempt to create roughly a 6 diopter back surface, since the approximate rotation of the eye at a 12 mm vertex distance is a 6 diopter curve. This means that conventional lenses have only one ideal base curve for every prescription.  Free-form makes that less rigid because the compensation as the eye rotates away from the optical center can correct for the peripheral cylinder when accurate POW measurements are specified.


Patient Personalization: The newest level of customization available is based on patient preferences. All progressives have to obey the same laws, which defines that the amount of unwanted cylinder in a design is based on the add power of the prescription. There are, however, subtle ways that the corridor can be adjusted within those laws. By incorporating different factors about how the patient wants to use their lenses, the design can now be geared ideally for that patient.