Does size really matter?
So, imagine you have someone perusing your sunwear frames and they seem to have found something that they like. One of the higher end, larger, high wrap frames. They’re pretty popular now, so it’s no surprise that they’ve picked it. You make your way over to see if you can help them with anything, and hopefully to close the sale. That’s when you get a good look at them.
Oh Crap. Is all you can think. You just saw it. They are one of those people. A high myope – and they are holding one of the largest frames that you carry. It also needs at least a six base lens, unless you want to have it completely splayed out. Oh, and their PD is pretty close to that of a ten-year-old. So, now you have one of those perfect storms. Where, thanks to the inexplicable nature of the English language, we use the word ‘perfect’ when we really mean ‘crappy’. You have someone that wants to give you a rather impressive sum of money, but it’s going to require you to do the impossible. You know what you should do but, then again… money. You can carefully weigh your options, which seem to boil down to making one of two choices:
A) Try and talk them out of it. You could try and get them into a smaller, flatter frame. This is, of course, the more sensible option in terms of your sanity. It helps you avoid issues getting the lenses made, and avoiding callbacks about lenses not being thick enough, not cutting out, or whatever else. Since life is never simple, this choice is also the most likely one to result in the customer going somewhere else. They found the perfect frame, and it’s your job to ‘make it work’, regardless of whether or not it’s actually possible.
B) Do it. You can smile and tell them that it’ll be no problem, and take your chances with what you get back once you order it. Maybe it’s easier to call them later and tell them what they ordered isn’t possible, and that they need to pick a smaller frame. That way, it isn’t you that is telling them ‘no’, it’s the lab. You tried your best, but the lab just couldn’t manage to break the laws of physics enough to make their prescription work in that frame. Besides, you can always have someone else make that phone call so you don’t have to deal with it. So that’s okay, right?
Neither of these two options usually result in everyone being completely happy. I say ‘everyone’, but I really mean the customer. Your happiness, unfortunately, comes a distant second. The question then becomes what, exactly, are we going to do in order to try and have some kind of a middle ground here? Some kind of an alternative option to give us at least a possibility of making this work. This is where we can use free-form surfacing techniques to to try and give ourselves some more options when it comes to high prescriptions in large frames.
Our third option (option C) goes by a few different names. It can be “lenticularization”, “edge thinning”, “blending”, or probably a whole host of other (probably catchier) names. Regardless of what the name is, they function in a similar way. The technique involves defining a central “viewing area”, which serves as the part of the lens that the wearer is actually going to look through. Outside of this area is where you get the blending zone. Instead of continuing the lens curve as usual, in this zone the curve will flatten out very quickly. This results in a part of the lens that the wearer can’t see through, but that ends up being much thinner than it normally would be.
The first objection that I can hear is that having part of the lens you can’t see through is going to cause problems. Seeing through lenses is pretty much the point of doing all of this, so I certainly understand the concern. Generally, however, this doesn’t really end up being an issue. This zone is usually far enough towards the edge of the lenses that the wearer isn’t going to notice it the majority of the time. This is especially true when dealing with a patient with a high prescription. They aren’t accustomed to using peripheral vision very much, since most lenses have too much peripheral distortion for them to get any meaningful vision out of that area. They tend to point their head instead of moving their eyes, which makes them less likely to notice an issue with the blending.
There’s a few different facets of this technique that you should be aware of – like when to use it, and when it isn’t going to help. Depending on the free-form design that you are using, you may be able to employ this on single vision, progressives, or even bifocal lenses. As an example, you can use it in conjunction with these lens types when using eagle™ LENSES. If you use a different lens design you should consult your lab for details on whether or not they have access to this kind of technology, and what they can do for you.
Before I go too much into what this blending does, I wanted to touch on the ‘why’. The general problem that this is intended to solve is that of lens blanks not being thick enough. Lenses start out as blocks of material (plastic, glass, or whatever) that have a curve already cut and polished on the front, with the intent of having the back cut (called semi-finished or ‘blanks’). The lab takes these and puts the prescription you ordered on to the back of it. Unfortunately, these lens blanks only come in certain sizes, base curves, and thicknesses. If you have a prescription too high, or a frame too large, it can easily happen that the raw material that the lab has to work with just isn’t big or thick enough to do the job. Sometimes they can special order (because we all love special orders) a thicker lens, though often thicker lenses simply aren’t made, depending on the material and color that you want. At that point, you’re usually stuck having to pick a smaller frame to make the job work. Sometimes you have an option to change material or color as well (i.e. only in clear plastic), but that’s usually not terribly helpful in making sure the customer is happy.
What lenticularization can do is make it so those previously “not thick enough” lenses will work. It functions in two different ways, depending on whether the prescription is plus or minus. For a minus lens, there are two main areas it can be helpful. Firstly, it allows us to get much higher prescriptions on the back of a plano front, while trying to minimize the edge thickness. Once you get to the higher minus (around -20 or so), usually you don’t have a whole lot of options, regardless of how good your frame selection might be. Sometimes this is where a bi-grind might be used (having a concave surface on both sides of the lens). The downside to this can be the cosmetics, but also the reduced availability of material and color options. When you need to surface both sides of the lens, that usually precludes any polarized or photochromic options.
In addition to giving more options for extremely high minus, this also makes it possible to get higher minus prescriptions on base curves they may normally be too steep for. My example for this was a personal pair of sunglasses, with the prescription being around a -12.00. I wanted to put it into a six-base wrap sunglass frame to see what the result would be, and it helped me see exactly how this technology can be useful. Now, you don’t need a prescription that high to see a benefit, even a -6 or -8 on a six base lens isn’t usually considered part of the normal Rx range for a lot of frames. What we are able to do is retain the central zone for viewing, and then blend the rest of the lens to reduce the thickness, which can make the job thinner, but also makes the impossible possible.
Especially when considering wrap sunwear, there are a few things that you need to consider regarding the lenses. Just because someone can make uncut lenses for the frame, doesn’t then mean those lenses are going to fit in the frame and look good. If you end up with a brick of a lens, it really doesn’t do you any good – you may as well not have ordered it in the first place, because you know there’s no way that the patient is going to accept it. With many of these frames you can’t really have any material hanging out in front, and you need to have all of the lens hanging out the back. This can quickly lead to an issue where the patient can’t wear them without poking themselves in the eye, because there’s too much lens hanging out. This is assuming, of course, you can get something like that into the frame to begin with. It’s very possible that it just won’t fit because it’s beyond what the frame designers imagined would be going into the frame.
While lenticularization on minus lenses lets us manipulate both thickness and base curve, it’s not quite the same with plus lenses. Here, we can still manipulate thickness, but this does not allow us to use a flatter base curve to achieve the Rx. We still need enough plus on the front to achieve our desired prescription, whereas with minus we can just add more minus to get our desired prescription. When using this for a plus lens, we are again ‘blending’ the outer edges of the lens. Instead of ‘chopping off’ the curve, however, we simply have the front curve of the lens end before the edge of the frame, and then continue outward with less material. This gives us what the professionals in the lab business call the “flying saucer” or “sunny-side up egg” look. Exactly how extreme of a ‘flying saucer’ look you get depends on how steep the original base curve of the lens is.
At any rate, it’s still up to you to decide how you’re going to handle the situation with your patient, and what you’re going to do to strike that perfect balance where they are happy and you’re still sane. It can be good as a business tool since it can open up the effective range of prescriptions you can do in higher wrap frames. Once you’re comfortable using and explaining this, it can certainly become a good way of retaining patients and improving your bottom line. Keep in mind, of course, that using this technique isn’t something you’re going to do every day, but it doesn’t have to be. It’s good to have it in your toolbox for when you need it, as in those situations where you do need it, you’re going to be glad it’s there. It’s always better to have an option as a backup, as opposed to having to tell someone ‘no’. That way they have some options, and don’t feel quite so left out of the process.
– Dirk Diggler