Photochromic is a generic term to define a lens with a characteristic of changing state from clear to sunglass dark when exposed to light. Over the years this option has been available in many different chemical, material, and color combinations; as well as offered by many different manufacturers with varying methods for application. Below is a list of the most popular flavors of photochromic lenses and a brief overview of the technologies and the companies that produce them.
Transition lenses were created by PPG Industries (Pittsburgh Plate Glass Company). Transitions lenses use a technology called imbibing to place the photochromic dye photosol a few microns below the front surface of the lens. The advantage is that the lenses can be surfaced to a very thin center thickness without worry of the photochromic properties being changed. This technology also allows for uniform color in cases where the thickness between right and left lens varies. Transitions is available in a CR-607 monomer 1.5, a CR-424 UV curable monomer 1.55, and a urethane 1.67.
Photo Grey Extra and Photo Brown Extra are the original glass versions of a photochromic lens. These lenses used an en masse technology which had the dye mixed throughout the entire lens. A large disadvantage to en masse technology s the fact that with varying thicknesses the lenses would have a slight variance in color, this is apparent in plus lenses with darker centers and minus powers with lighter centers. The chemical commonly used in these lenses is silver halide which is also a popular dye used in photography for film and paper.
Sunsensors are an en masse plastic technology created by Corning. Corning offers this lens in a 1.56 material. Sunsensors use an en masses technology yet lenses will match one another even with varying thicknesses and powers, the idea behind this is that only the surface dye is activated so no matter the variation in thickness the UV light is absorbed and activates the same amount of chemical in the surface of the lens.
LifeRx lenses were created by Vision Ease to fill a niche for polycarbonate FT photochromics. The technology used to create theses lenses is a dye film that is applied to the lens similar to a polarized film. The advantage is that FT polycarbonate photochromic lenses are finally available for sale, however the disadvantage is the same disadvantages polarized lenses face; delamination which the earlier version experienced and contra indications for use in nylor mounts. None of these disadvantages have stopped the LifeRx line of photochromics from being widely accepted and heralded in the ophthalmic community. Especially among pediatric dispensers who were until LifeRx were limited to Trivex FT transitions.
Harry Chilignuerian ABO-AC NCLE COA