Today let’s take a look at several categories of proprietary lenses that made a big splash upon their debut, but with decidedly different track records through the last decade or two.
A. The iZon Lens – Introduced at the dawn of the 21st century iZon was a marketed as one of the first “high definition” spectacle lenses, specifically to address higher order aberrations. According to its marketing material, the lens represented a unique Rx as customizable as a fingerprint, and supposedly improved depth perception and contrast. A significant application was improved night vision and reduced starburst patterns particularly after refractive surgery, when considerations of wavefront technology began to peak.
The Ophthonix Z-View aberrometer.
The lenses were pricey, and hit the height of their marketing popularity in 2007. Despite the involvement of some movers and shakers in Optometry touting its benefits, only a limited number of eyecare providers prescribed iZon wavefront lenses, and patients apparently did not experience sufficient benefit, to survive in the marketplace. In October 2012, Ophthonix announced it was ceasing operations after 11 years of business.
B. The ChromaGen Lens -As the name of the lens implies Chromagen was originally introduced for its effects on color vision. It’s inventor, David Harris, Ph.D, then branched out into the lens as an application for dyslexia, which was a decidedly hotter topic in England at the time (early 21st century) than in the United States.
ChromaGen still has a website, but if you try to locate a provider in the U.S. you’ll be directed to a provider based in the Netherlands. Suffice it to say that the spectacle lens version for reading difficulties was never prescribed by enough eyecare providers, or provided sufficient benefit to enough patients
C. The Neurolens – I blogged about this lens six years ago, and it has progressively been gaining a foothold in the ophthalmic marketplace. As with the iZon and Chromagen lenses, its marketing targets a niche population of patients with problems unresolved through conventional lenses. As the iZon lenses did, it requires a proprietary measuring device, in this case for specific binocular vision parameters, to generate a proprietary Rx available only through a specific lab.
The proprietary lenses consists of “contoured prism”. The contour is a base-in prism that progresses from zero at distance to 0.375^ per lens at near. So if no prism is incorporated at distance, the patient obtains a “contoured” (progressive) effect of 0.375^ BI at near. It is additive, so the full BI^ effect is 0.75^ in downgaze, essentially a mini version of the way a progressive addition lens works with plus power added at near.
If hypothetically 0.75^ BI is Rxed at distance, as the diagram shows below, the lens provides a “contoured” effect progressing from 0.75^ BI at distance to 1.125^ BI or a net effect of 1.5^ BI OU at distance and 2.25^ BI OU at near.
There are several noteworthy things about Neurolens. One is that it is targeting patients who respond to a progressive mini or microprism base-in effect. The target population is therefore patients with convergence insufficiency, who are the primary group with nearpoint symptomology. Another is that there is only one contoured prism value is available. That would be analagous to the first progressive lens being marketed to, ODs with one low add power helping all patients with presbyopia. Much as that low add can be layered onto any distance power, and will help some of the patients with presbyopia, it would be far from a panacea. Which brings us to the third point that the proprietary device (NMD2) used to measure binocularity doesn’t address accommodation at all. While it makes sense that many patients with nearpoint symptomology can be helped with a progressive mini-prism base-in effect at near, at least some of those patients would do better with low plus at near, or a combination of the two.
Recognizing this gap, Chadwick Optical came out with its Converge Lens, combing the 0.37^ BI of Neurolens in each lens with +0.87D. Higher nearpoint prism values are available, but one can only obtain that by incorporating higher amounts of plus lens power. So the contour or progressive nature of the prism is similar but not identical with the Neurolens and the Converge Lens. Of note, there is no proprietary device necessary to order the Converge Lens.
It is too early to tell how well history will view Neurolens in its rear view mirror. Its marketing effort alone confers an advantage over the fate of iZon and ChromaGen lenses. It is an approach to a segment of the population that comes with some caveats, as our colleague Dr. Cam McCrodan points out in this video:
Interestingly the limitations of the NMD2 measuring device to a practitioner conversant with binocular vision and vision therapy is precisely what makes it attractive to a primary care practitioner. Listen to the opening minute of this roundtable marketing video recorded at Vision Expo West last year.
A primary care New Jersey colleague who I highly respect for many reasons, Dr. Ray Corbin-Simon, says the following: “I do phorias just because in the state of New Jersey, it’s required. But, you know, am I really looking at the phoria measurements as if there’s something wrong with the patient in terms of prescribing something for them? I never really thought about it until Neurolens, right? So I think that variability is going to be there depending on the individual practitioner as well.”
As a follow-up to that comment, the moderator, Dr. Paul Karpecki, another highly respected primary care colleague, observes: “I remember learning binocular vision testing and then when I graduated hoped I didn’t have to know it again. And I was never really good at it. Like (with) von Graefe it was tough for me to find the right end point. Maybe because I had in my mind it was difficult already, and it was. And I tried again and they’d be off a little bit, and I’d say which one is this? I could never get really good accuracy. Even cover testing, I’d watch for movement of their eyes but that didn’t always happen so it was more of this gross evaluation. So I was one that never liked to do von Graefe binocularity. I love the ability to put them behind a machine and in a minute and a half I’ve got everything I need and so much more accurate than anything I could ever imagine doing. And the NMD2 practically tells me exactly what to prescribe.”
Which brings me to a final consideration, which is the potential therapeutic application of these lenses. Neither iZon nor ChromaGen lenses would be though of as therapeutic, in the sense that there is no illusion about the patient being able to re-calibrate higher order aberrations or color-related abnormalities. While the lens is being worn, it has an impact. But when the glasses are removed, the underlying deficit persists. But what about the underlying binocular abnormality of convergence insufficiency which Neurolens is targeting?
Elsewhere I’ve established that microprism can have a neurotherapeutic effect. When applied in that manner, the patient can often be weaned off the prism, with the underlying binocular anomaly resolved, or the binocular instability having stabilized. However, one does not get the impression from Neurolens marketing material that the lens has any therapeutic benefit that would change the underlying condition. (If the same philosophy were applied to vision therapy, then one would need to remain in vision therapy indefinitely to remain asymptomatic.) Listen to the doctor at the 1:32 mark of this video segment:
“I have to say that one of the other things as a doc is, you know, when you see something that has a high price point, some docs will say ‘Great! That’s going to bring my revenue per patients up!’, and other docs will say: ‘Ooh, how am I going to explain to patients that they’re going to have to pay this price out of pocket?’ And I am at the point now where I am having patients come back that I’ve already prescribed Neurolenses for previously, and I’m always waiting for them to say ‘Can I get a regular pair this year and not do the Neurolenses’, but absolutely not! Once you fix that for them, they’re going to stay in them and keep them.”
D. The Shaw Lens – For the sake of completion, I’ll mention one other type of proprietary lens. The Shaw Lens pioneered by Dr. Peter Shaw in Canada, is aimed toward a different kind of binocular problem in which anisometropic lens values result in aniseikonia. In fact, eikonic lenses were all the rage in the 1930s, when they actually made front page news in the The New York Times. That too required a prorprietary device known as the space eikonometer manufactured by American Optical, a company that fabricated eikonic (or eisokonic) lenses to equalize image sizes between the two eyes based on those measurements. But the instrument eventually made it to the scrap heap of ophthalmic devices and the popularity of dealing with aniseikonia waned through the years so that by the time I went through Optometry in the 1970s it was already an after-thought. Dr. Shaw decided to revive the concept of eisokonic and eisophoric lenses without the need for a proprietary device.
“Designing lenses that take into account how both eyes work together is not an easy task. The math is complex in a purely theoretically environment but when you factor in other variables like frame dimensions, the position of the glasses on an individual patient’s face and the limits that lens manufacturing and optics place, it’s no wonder why no one has done this before.
That’s what makes the SHAW lens unique. The SHAW lens process uses a patent-pending method to accurately model eye rotation in order to predict distortions caused by eye glasses. We then use that information to design a lens that reduces or eliminates the distortion other lenses can cause.
The key to making a SHAW lens is the measurement of Motor fusion (vergence) limits by the optometrist using Risley prisms on the phoroptor. It’s these tolerances that make all the difference.”
Instead of a proprietary device, Dr. Shaw has the practitioner supply key information collected during a binocular vision evaluation, and supply that through downloadable software as a design tool. The laboratory then uses a proprietary algorithm to fabricate the proprietary Shaw Lens.
Dr. Shaw is a fascinating individual, an optometrist with a background in physics and computer science. As background information, you can listen to this podcast interview with Dr. Shaw conducted by Dr. Nathan Bonilla-Warford.
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