Digital / Freeform Lenses
Digital Lenses / aka Freeform Lenses
Digital lenses, also known as freeform lenses, are lenses produced with the latest, most state of the art equipment. To explain why digitals lenses are better, we must first discuss how all prescription lenses have been “traditionally” fabricated.
Traditional Lens Fabrication
Traditional lenses, like with new digital lenses, require having multiple pieces of equipment, each having their own specific role, to fabricate a prescription lens. To start the process, a proper lens blank is required. Lens blanks, known as semi-finished lenses, are available in a wide variety, due to all of the choices of lens styles (single vision, bifocal, etc.), materials (plastics or glass), and special features like Transitions, or Polarized. Each type of lens blank also has a range of varying curves, known as base curves (BC). When dealing with multifocal lenses, you also have a range of bifocal “add” powers to consider. So, with all of these variations, there are thousands of lens blanks manufacturers have to produce.
These lenses, produced by a manufacturer, use molds of each and every base curve (and every separate “add” power for bifocal lenses). A plastic resin (CR-39, polycarbonate, hi-index, etc.) would be poured into the molds, producing a semi-finished blank with a specific base curve. With all traditional progressive lenses (PAL), the design is always produced on the front surface, along with the BC via the molding process. These blanks then go through different processes to produce the prescription. Next, the lenses are inspected, cleaned, placed in labeled packages, categorized, and prepared to be shipped to lens laboratories all over the world.
A laboratory will try to stock a large variety of commonly used lens blanks. To start the process to produce a pair of lenses (referred to as a job), a specific pair of blanks are pulled by base curve, material, and if a multifocal, an “add” power. A protective finish is then put over the front (BC) of the lens. A “lens block” is then attached via a substance that resembles a waxy plastic or lead-like liquid (lead is no longer used). This block holds the lens in the different machines as it continues through each process. One of the main pieces of equipment that separates traditional lenses and digital lenses is the generator. This machine uses a large, diamond embedded grinding wheel that is worked back and forth across the back surface of a lens blank to produce a rough set of back curves and a specific thickness. Additional processes beyond the generator allows the lenses to be polished to a clear finish, while removing tooling marks (generator marks) from the back side.
**Traditional Lens tolerances are 1/8th of a diopter.
Digital / Freeform Lenses
Digital lenses have similarities, but there are some major differences that make the optics noticeably more comfortable, crisper, and sharper, specifically for single vision lenses with high corrections, and PAL’s. Currently, there are a few laboratories producing Flat Top Bifocals and Trifocals digitally, but unless the patient’s refractive error is excessively high, there is not too much noticeable benefit to pay the extra money for digitally produced single vision or flat top multifocals. This is my professional opinion of course.
Digital lenses do require most of the same features to produce a prescription lens. There has to be blanks with specific BC’s and the different types of materials. The equipment used to produce digital lenses have similarities, yet some major differences. Digital lenses are designed with computer software that tell specifically designed machines how to tool the back surface of the lens blank. The generator for these lenses is designed like a router and is controlled by the software.
Single vision and PAL, digital lenses are produced from single vision lens blanks. If you’ve been able to digest all of the material you’ve read so far, a light bulb should have just gone off in your head. Did you catch what I just wrote? Digital PAL’s are produced from a single vision lens blank! The PAL design is produced on the back side of the lens by these machines and computer software. Traditional PAL’s have a molded front design – produced from molds. This is one of two major differences to why digital lenses offer crisper, clearer, and notably more comfortable vision. Producing a PAL design on the back surface puts that design closer to the eye. Having the design closer causes the brain to feel much less “swim” in the lens, and it gives a wider field of vision as the eye travels downward through the corridor of the lens. Second, the optical tolerances produced are within 1/100th of a diopter, compared to a traditional lens with a tolerance of 1/8th.
For these reasons, any person wearing a PAL will have more noticeable crisp, sharper, and comfortable vision with digitally produced lenses. Yes, they do cost more money, but think of the added benefits. Benefits that people don’t really think about are how these lenses can make our everyday lives safer. Having crisper, sharper, more comfortable vision helps improve reaction time, in the case of an emergency…… ever think about that? Don’t forget about making your sunglasses digital polarized lenses too!
Also, keep in mind, traditional lenses are perfectly fine. People have been wearing them for years, and will continue to wear them and be happy. First and foremost, the goal is to improve eyesight. It doesn’t take a digitally produced lens to achieve 20/20 vision. Think of this topic like automobiles. If you were going to drive across the state, you can do it perfectly fine in a Honda Civic, but think about how much nicer the ride would be in a Cadillac.