Digital Lens Design, New Materials Make For High Definition Vision


The ophthalmic lens industry has undergone a revolution in the last few years, the benefits of which, I will describe in this article. New materials, new digital lens design technology for both single vision and progressive lenses, and new multilayer anti-glare, anti-smudge, anti-static and scratch-resistant coatings, have made vision correction with glasses unlike anything you have seen before…a true high-definition experience.

You are probably familiar with other older lens materials, such as glass, plastic (CR-39), and polycarbonate, since these have been around for many decades. In 2001, however, self feeding spoon a new material became available, called Trivex, and it is the only material other than polycarbonate which can withstand the FDA Impact Resistance Test, the High Velocity Impact Test and meet ANSI Z87.1 ’89 standards. Trivex has an index of refraction higher than regular plastic and is lighter weight than polycarbonate, as well as being far superior in optical quality due to it’s lower aberration. It also has inherent UV blocking properties and it’s higher tensile strength makes it more suitable for drill mounting in frames than any other material. Aspheric lens designs in Trivex, ensures even better optical quality for your prescription lenses.

There have been several milestones in the ophthalmic lens industry’s evolution. The introduction of CR-39 plastic in 1946, and the introduction of the first progressive addition lens (PAL) in 1959, to mention two. Digital lens design, also called free-form design, is another such milestone.

Until now, spherical and astigmatic lenses have been surfaced by a process called “milling,” done on a machine with a diamond coated wheel, a so-called generator. After this is complete, a smoothing step is done, known as “fining,” using a hard tool with an abrasive pad on it. These tools are called “lap tools,” and optical labs traditionally had to have towering racks filled with these tools, since every curve power required its own lap tool. Furthermore, the labs had to follow this step with a polishing step, using another, less abrasive pad and polishing mixture. The modern optical laboratory contains many rows of machines performing each of these steps, with many optical lab technicians monitoring each machine’s progress. As you can guess, this is an expensive and time-consuming way to manufacture lenses. The accuracy level of this type of production is ± 0.25 diopters (the unit of optical power.)

Digital surfacing, however, is done with a computer-controlled machine with a single diamond point cutting tool. This allows the optical lab to generate the patient’s prescription, the progressive lens design, account for how the glasses are worn on the face, and also incorporate aspheric design all with one pass! The cutting tool works in 3 dimensions at once, not just two like the older machines, and the accuracy level is ± 0.01 diopters. Because the entire design is on the back surface of the lens, the patient gets a larger field of view and less aberration with the finished lens. The resulting surface cut this way is so smooth that the “fining” step is eliminated, and the lenses go straight to polishing. Because the digital (free-form) surfacing process is so highly automated, fewer hands need to be involved and speed of production and quality are improved. The cost of this technology is actually lower than many others charge for the older type of lenses!

Premium multilayer anti-glare lens treatments are designed so that each layer of the treatment (or stack) has a specific purpose. The combination of chemistry and physics used in the creation of these treatments produces a product patients can purchase with confidence.

Early anti-reflective (AR) coatings used a single layer of magnesium fluoride to create the AR treatment on the back surface of the lens. Since visible light consists of over 400 wavelengths, eliminating only one of them was not particularly effective. To eliminate reflections across the visible spectrum, multiple layers of coatings are needed. Modern anti-glare treatments employ multiple interrelated layers that have different functions, known as the “AR stack.”

 


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