There are many patients who feel they completely understand some basic technologies in this field–they aren’t always ENTIRELY correct about this. In particular, Anti-Reflective (or No-Glare) and Photochromic (or light-changing) lenses have been around for decades. Whenever a technology has been around for a long time, there can be misconceptions about how it works, or even how different versions vary, simply because the point of reference from experience is with an older version of the technology.
The purpose of anti-reflective coatings is to minimize the amount of surface AND internal reflections. This can be mildly complicating to explain, but I think it’s possible to boil the benefit down to something digestible without injecting too much science. At the most basic, all anti-reflective coatings bend wavelengths of light so that reflections can be cancelled out, allowing more light to reach the pupil, and thus increase clarity of vision. This benefit applies to all prescriptions, but can be more noticeable with certain prescription types. Generally speaking, if you need glasses to see distance, or to work on any kind of digital device, you will notice the improvement in clarity.
Where Anti-reflective coatings vary is what they do beyond the removal of reflections, as well as how much reflection can they eliminate. Generally speaking, the more expensive the coating the more it does for you. This should be obvious, but as with so much in our field, many patients can believe there is essentially just one version and it’s all salesmanship and false promises to “upgrade.” I’m here to tell you that there is most definitely a difference amongst the coatings out there.
A standard uncoated lens loses approximately 10% of all light to reflection. A portion bounces off the front, and this is what othere people see. It’s the cosmetic side of what AR does for you. But the greatest concern, from an optics perspective, is that a portion of the light enters the lens, bounces off the backside of the lens, bounces back to the front, and then continues towards your pupil. This “internal” reflection creates a ghost image on your retina. You see what you’re supposed to, as well as this faded, just off alignment, false image. When you are in a darker environment, with points of light, this ghost image is very hard for your brain to filter. So, when driving at night, for example, these additional reflections can be very distracting.
Above are some examples of how different coatings can appear. You’ll notice that there is one coating with a slightly blue hue. This particular version is designed to maximize light transmission to the highest level possible. But this isn’t the only thing that varies amongst coatings. In addition to removing reflections, they can also improve scratch resistance, repel water, and oil, or even add an anti-static layer so that you need to clean your lenses less often (because dust is repelled). The coating process is quite involved, and can take as long as 24 hours to complete in a vaccuum chamber.
The technologies involved in creating photochromic lenses have evolved in significant ways since the first plastic versions were created in the early 1990’s. The earliest version was only available in one type of material, and it’s responsiveness was less than ideal. The older versions never got fully clear, and didn’t get particularly dark in the sun…unless it was cold out. As a native of Northern California, and one of the earliest guinea pigs for this original version, I discovered those limitations in a profound way. I got my first pair just as I was leaving for college in San Francisco. The relative chilly weather in the City left my lenses permanently around 50% tint. Too dark for most activities, but not dark enough in the sun.
Since that first version almost 30 years ago, things have improved dramatically. The lenses can now reach 80% or more in bright sun, and are virtually clear indoors. On top of that, there are many versions…some are light sensitive, some are UV sensitive, some become polarized, and there are many color options as well.
Far and away the most well known version of photochromic lenses are called Transitions, but there are other technologies out there. It’s important to have a discussion with your optician about what you want your lenses to do, to make sure you’re choosing the right one.
Anti-reflective treatments are important for pretty much every pair of glasses. It’s always going to make your vision sharper, and most often the complaints associated with Anti-reflective coatings are about earlier versions, or cheaper versions. The best versions reduce smudging, as well as scratches.
Photochromic lenses aren’t necessarily for every patient, but the advancements in the technology has taken them much closer to hitting that mark. Even if you’ve had a negative experience in the past, it’s worthwhile to discuss the changes with your optician to see if they can be a good solution for your needs now.
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