As spring approaches, the ECP’s mind turns to the newest developments in the optical field. And with all the conferences that occur in March, who can blame them? While many concentrate on the latest designer frames and fashions, it is important not to forget the up-to-the-minute lens trends.

Free-Form Technology What is Free-Form? The answer varies depending on who is asked. Some will respond that it is a particular brand of lens. Some will tell you that it is digital surfacing, direct surfacing, or wavefront technology, without really explaining what these terms mean. Others will respond with a shrug and a blank look. This is because Free-Form is a complex topic that, while introduced in the United States in 1996, has just begun to really catch hold in the optical industry. Due to the custom nature of the product, the technology is called by different names and is produced differently by every different manufacturer. As a result, confusion is prevalent in the field.

It is important to remember that Free-Form is a way of digitally surfacing a lens, not an actual lens design. In conventional lens surfacing, a semi-finished blank is placed in a generator and the back of the lens is ground away. The resulting rough surface then goes through a process of fining and polishing, utilizing either a soft or hard lap. Due to the restrictive nature of the fining and polishing, as well as the limiting nature of semi-finished lens designs, traditional lenses could only have spherical and cylindrical surfaces and could only be produced with accuracy up to +/-.12 diopters. However, this is not the case with Free-Form lens surfacing.

In Free-Form surfacing, a computer numeric controlled (CNC) generator is controlled by a point file software system. This software can apply over 10 million calculations to create a data file that includes the patient’s prescription, parameters and desired lens material. The data file is then sent to the CNC generator and the lens surface is cut into the lens using a natural diamond point cutting tool. An Additional factor in the lens grinding process that is unique to Free-Form surfacing, is that the front as well as the back surface of the lens can be ground. As a result of the dual surfacing as well as the exact nature of the cuts, almost any type of lens surface can be cut into the lens. After completing the time in the generator, the lens can proceed directly to the polisher, skipping the fining process. A soft pad polishing system is then applied to the lens to safeguard the new curves on the lens surface that usually has only about 1 micron variation in depth. 

Different Methods of Free-Form Surfacing

Each manufacturer has their own Free-Form design that is unique to their manufacturing process; however, most can be classified in four different areas.

1. Internal Technology- This is when a lens has a spherical front surface with a progressive back surface.

2. Dual-Add Technology- In this technology, the Add power is ground on the front and back surface of the lens.

3. Conventional Front Technology- One of the earliest digital surfacing techniques, the lens has a front surface with a conventional design and a specialized surface on the back side. This technology is not seen very often anymore.

4. Progressive Front Technology- The lens with this surfacing technique has a front surface with a progressive design and an aspheric/atoric design on the back surface.

Each surfacing method has its own unique advantages according to its manufacturer. Seiko is a leading manufacturer of Internal Free-Form with their Succeed and Supercede lenses. According to the manufacturer, the benefits to the 100% back surface technology are wider fields of view, less front curve distortion, and greater prescription accuracy for distance, intermediate and near.

Essilor is currently the major manufacturer of Dual Add technology. In January 2009, the company released the Definity and Definity Short lenses with Dual Add 2.0 The manufacturer claims that by having the Add power ground on the front and back, the transition is smoother, the vision is clearer while looking down, and there are wider fields of vision at the distance, intermediate and near.

Progressive front technology is being utilized very effectively by Hoya in their Hoyalux iD. By combining two aspheric/atoric progressive lens designs, the manufacturer believes that they have achieved unlimited visual sharpness, extremely wide fields of view and perfect near and far transition. 

Remember, not all Free-Form designs are created equal. Just become a lens manufacturer claims a lens is Free-Form, it doesn’t necessarily mean that the lens is better than a traditional design or that it is right for the patient. If the lens blank is not of superior quality or if the process fails in any of the manufacturing steps, the result can be a disaster for the patient. Therefore, the eye care professional should choose his or her Free-Form lens carefully. It is important for the ECP to research the manufacturers and labs in order to find one that he or she is comfortable with and can rely on. Fortunately, there are many innovative and influential manufacturers to choose from.

Understanding the Benefits

Now, what does all this mean to the eye care professional and patient? 

• Greater fields of vision. The intermediate and near portions of the lens are widened, with greater visual acuity in all vision zones.

• Minimal distortion. The technology helps to eliminate the “swim feeling” and lowers the levels of unwanted astigmatism.

• Fitting the extraordinary. Every eye care professional has encountered the patient who cannot wear a multifocal lens. One of the principal reasons for the individual’s non-adapt may be due to the “average” nature of traditional progressive lenses. Conventional semi-finished lenses are very constrictive by design and therefore, can be difficult for some patients to use effectively.

• Specialty lenses are now more readily available. Free-Form technology is not just for progressives. Complicated atorics, slab-off prisms, blended bifocals and steep wrap designs are all benefiting from Free-Form surfacing.

• Customization. The difference between a well crafted Free-Form and a traditionally designed lens can be similar to the difference between a high definition and analog television or a tailor-made suit and one that is off-the-rack. Both can work for the patient, but one is more visually appealing.

atLast! Lenses

Launched in October 2008 by PixelOptics, the atLast! lens is designed to replace the use of lined bifocals by individuals who do not wish to wear a progressive lens. A composite lens (its technical name is Composite 67), the atLast! lens is manufactured using a 1.67 hi-index material for the rear part of the lens and Trivex for the reading component of the lens. This combination is not a laminate, but a molecular bond creating a one piece lens, thereby eliminating the separation problems that typically occurred during the processing of older composite designs.

Conventional Bifocal

atLast™ Enhanced Multifocal

atLast! works by taking advantage of the differences in the indexes of refraction of the Trivex and 1.67 material components, and by Adding a power gradient to the front segment and an embedded power segment in the rear lens component. To understand this more clearly, take the following example: A patient has a +2.25 Add. The rear component lens will have an embedded power segment of +0.75. The front component segment will have three continuous zones of plano, +0.50, and +1.50. The end result is a lens that has four zones of vision; distance (greater than 5’), far intermediate (29” to 5’), intermediate (18” to 29”) and near (12” to 18”). 

Since the atLast! lens is new to the market, it is helpful to know the current prescription ranges, as well as fitting procedures. At this time, atLast! is available in spheres of +3.50 diopters to -6.00 diopters, cylinders up to -4.00 diopters, and Add powers of +1.75 to +3.00. When fitting the lens, it is important to allow for the intermediate area, so it is best to fit 2-3mm higher than the lower lid and to have a minimum fitting height of 14mm. 

There are several benefits to the patient and eye care professional.

• Increased intermediate vision. Standard lined bifocals and trifocals do not have a correction for far intermediate areas. As a result, advanced presbyopes in these types of lenses have a definite disadvantage in their visual acuity at these areas.

• Significant reduction in image jump.

• An effective alternative to progressive lenses for previous non-adapts.

• Greater cosmetics due to a less visible segment and reduced ledge thickness.

Conclusion

This is an exciting time to be in the optical field. New lens designs are being introduced and improved upon at an astonishing rate. As lens technology improves daily, it is the job of the eye care professional to stay aware of the latest developments in order to provide the patient with the best care possible. Today’s patients are well informed and deserve the latest and best in technology and it is up to the ECP to give it to them.

Carrie Wilson
BS, LDO, ABOAC, NCLEC