|The 1.56 and 1.60 indices of Signet Armorlite’s KODAK InstaShades lenses use a 1.0mm thick photochromic layer chemically bonded to the substrate.|
Understanding the various techniques of manufacturing photochromic lenses will help you make a more informed decision on which one to recommend.
Photochromic lens technology has been around for over 70 years. In the early 1940s, Corning Ophthalmic began experimenting with photochromic lenses but it wasn’t until 1962 that its PhotoGray® lens made it to market. Since then, many players have entered this lens segment.
While almost all photochromic lenses activate to UV light, other activation wavelengths are being employed. And not all photochromic lenses are made the same way either. Here is a look at some examples.
The original process Corning used (and still uses) for its glass PhotoGray and PhotoGray Extra® lenses is known as “in-mass.” In this process, photochromic chemicals are added to the lens material and mixed so the photochemical compounds are distributed evenly throughout the entire lens blank.
In-mass technology provides a large number of photochromic molecules for a lens so there is little concern of the photochromic effect to “wear out” or diminish over time. Even so, in-mass manufacturing has a tendency to create powered lenses that exhibit uneven color when the lens power gets stronger. This uneven color is because the thicker portions of the lens have more mass and more photochromic molecules, which creates the darker “racooning” effect when activated. In turn, thinner portions of the lens become lighter in color.
Glass photochromic lenses retain a small amount of color, even during their lightest state indoors or at night. These lenses are also somewhat temperature sensitive, getting darker in colder climates, as well as at higher elevations. Segmented multifocals are more obvious in glass photochromics, as the segment itself is clear and fused into the photochromic lens. The photochromic lifespan of glass photochromics is virtually infinite.
In-mass technology is still a popular method of producing photochromic lenses, and in addition to glass lenses, it is used with plastic lens materials in products such as Rodenstock’s ColorMatic® Extra, which is available from Pro Fit Optix, and Corning’s SunSensors®.
Augen Optics advertises that its new AugenSOL™ photochromic lens has photochromic cells embedded throughout the material resin so as the surface of the lens wears thin, new photochromic cells are activated to replace them. This gives the wearer long-lasting, reliable photochromic performance. Offered in 1.50 index material, tests by the company indicate that AugenSOL lenses get dark in just 12 seconds while providing 100% UVA and UVB protection. They also fade quickly to a barely noticeable tint indoors.
Optical Dynamics’ (ODC) in-office digital lens casting system offers a photochromic polymer lens option called sunSMART™. Produced in the convenience of your office, these lenses are available in gray and brown and are now available in an extra dark photochromic called ultraSUN™. In-mass technology ensures a consistent photochromic effect that the company stands behind for the life of the prescription. For more information on ODC’s lens casting system, see “Cast Digital Lenses In-House.”
OptiCast also uses the in-mass process to produce its Shades™ lenses. Shades photochromic lenses have a 1.52 index and can be cast in standard gray and brown as well as six unique fashion colors: sky blue, golden, tangerine, pink, lavender, and turquoise.
Vision-Ease Lens’ new ChangeRx™ photochromic lenses are hard resin (1.50 index), manufactured with homogeneous in-mass technology. Photochromic dye molecules are mixed into and become blended with the plastic lens monomer. The organic, photochromic molecules are tailored for the monomer, resulting in fast, uniform reactivity. For more information on these new lenses, see Lenses New Product Gallery – April.
IMBIBING AND TRANS-BONDING
Transitions Optical, Inc. works with dozens of partners worldwide to treat its lenses so it can offer designs as Transitions® lenses, such as Essilor of America, Inc.’s DEFINITY® Transitions VI and Oakley® Transitions SOLFX™ sun lenses. In other words, Transitions Optical does not make any lenses itself, instead, it works with partners. This is one reason for the extensive availability of lenses with Transitions photochromic technology worldwide. In fact, most plastic photochromic lenses sold worldwide utilize Transitions Optical’s proprietary technologies: Imbibition and Trans-Bonding™.
With Imbibition, the photochromic compounds are driven 0.15mm into the front surface of most hard resin lens, becoming permanently imbedded into the surface and part of the lens. This means the photochromic materials cannot be scratched or peeled off.
Some lens materials are more challenging photochromic substrates. Polycarbonate is an example, so with materials like this, Transitions Optical uses a technique known as Trans-Bonding. This process applies
|Younger Optics’ Drivewear lenses use both UV and visible light to activate its photochromic properties.|
proprietary surface treatments in layers, which provide outstanding adhesion, scratch resistance, optical purity, and photochromic performance. Trans-Bonding technology allows lens materials previously considered unsuitable for photochromic processing to be produced with features equal to other lens materials.
Transitions SOLFX sun lenses come in eight targeted product options. These are sun lens options that use the Imbibition or Trans-Bonding processes.
UV AND VISIBLE LIGHT
According to the company, Drivewear® lenses by Younger Optics were the first to use both UV and visible light to activate its photochromic properties. In overcast or low light outdoor conditions, Drivewear has a high contrast green/yellow color that transmits about 30% to 35% of visible light. In daylight driving conditions, the lens has a copper color that transmits approximately 20% and highlights red and green colors for optimal recognition of traffic lights. In outside bright light, the lens turns a dark reddish brown and transmits in the low teens. Drivewear’s polarizing filter, in combination with its photochromic properties, helps the lenses reduce discomforting, disabling, plus blinding glare.
The Falcon NXT® lens from Julbo Eyewear features BWS (Behind the WindShield) technology, which reacts only to visible light rather than UV. This means its darkening is not affected by an automobile’s windshield. Made with Trivex® lens material, Falcon joins the line of NXT Varia™ photochromic lenses.
Transitions XTRActive™ activate using UV and visible light. The lenses have a light tint indoors and get very dark outdoors, even in warm weather. They also have a moderate tint behind car windshields.
Offered by Signet Armorlite, Inc., KODAK InstaShades® lenses are manufactured using various methods. The 1.56 and 1.60 indices use a 1.0mm thick photochromic layer chemically bonded to the substrate. Polycarbonate uses a 0.8mm thick photochromic layer that is molecularly bonded on a polycarbonate substrate. InstaShades 1.50 (1.508 index) is an in-mass photochromic material well-suited for drilling applications. When surfacing KODAK InstaShades 1.56, 1.60, or polycarbonate, the laboratory must adhere to minimum center and edge thickness guidelines to avoid processing into the photochromic layer.
Serengeti® Polar PhD™ RX lenses utilize the material tinting and casting process called Confined Tint technology. This technology places the photochromic dyes in the front surface of the semi-finished lens. The polarized film is positioned closer to the lens’ front surface, providing a center thickness of just 1.4mm. Carl Zeiss Vision Inc. is the exclusive North American supplier.
As more photochromic lens options become available along with improvements in lens material availability and manufacturing innovations, photochromic lenses will continue to grow their segment of the ophthalmic lens market.
Randall L. Smith is the Opticianry Program Director at Baker College in Jackson, MI.
WHERE TO FIND IT
866-284-3611 • augenoptics.com
Carl Zeiss Vision Inc.
800-358-8258 • zeiss.com/lenses
800-821-2020 • corning.com/ophthalmic
Essilor of America, Inc.
800-542-5668 • essilorusa.com
800-651-0833 • julbousa.com
800-733-6255 • oakley.com
Optical Dynamics (ODC)
800-587-2743 • opticaldynamics.com
888-893-cast • opticastusa.com
Pro Fit Optix
866-996-7849 • profitoptix.com
888-838-1449 • serengeti-eyewear.com
Signet Armorlite, Inc
800-950-5367 • signetarmorlite.com
Transitions Optical, Inc.
800-848-1506 • transitions.com
800-328-3449 • vision-ease.com
800-366-5367 • drivewearlens.com