Extensive OrthoK Research Confirms Efficacy to Slow Myopia Progression

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September 15, 2023

Following the publication of the paper “Efficacy of the Euclid Orthokeratology Lens in Slowing Axial Elongation” by Mark Bullimore, MCOptom, PhD, FAAO, and Maria Liu, OD, PhD, MPH, MBA, FAAO, John Sailer, Editor-in-Chief of Review of Myopia Management, caught up with Dr. Bullimore to find out what this means for eye care professionals who are using OrthoK to slow the progression of myopia.

Read the following interview to find out which OrthoK lens has been researched the most, why axial length is the preferred method of assessing myopia progression, the efficacy of Euclid’s OrthoK lens, and the real-world implications of this data.

John Sailer, Editor-in-Chief, Review of Myopia Management: You recently published a study with Dr. Maria Liu on the efficacy of Euclid’s OrthoK lens for slowing axial elongation. Can you describe the study and its results?

Mark Bullimore, MCOptom, PhD, FAAO: Maria and I both consult for several companies, and we’ve been working together with Euclid to conduct a literature review to see what was out there on the efficacy of the Euclid OrthoK lens design. It was very surprising to see how much work had been published. We identified 37 peer-reviewed articles in the paper where independent investigators reported the axial elongation in children wearing Euclid OrthoK lenses. In 12 of those publications, they had a control group wearing spectacles so you could assess the efficacy of the lens. So, the first finding, if you like, is that this is an incredibly well-researched device. The only treatment that comes close in the field of myopia progression is atropine. 

RMM/Sailer: Very interesting. We’re talking about the Euclid Emerald lens designed for orthokeratology. It’s been around for 20 years. What was your reason for doing the study now?

Dr. Bullimore: Part of the driver for this was to look at the efficacy of the lens in slowing axial elongation to make sure the information is up to date. In looking at the data, we thought we should publish these results given the 20-year anniversary of Euclid’s OrthoK lenses being available in the U.S., to see how consistent the conclusions are.

RMM/Sailer: Makes sense. Interesting results, too. So, some specific results were “the mean 12-month efficacy, difference in axial elongation, was 0.18 mm, and the mean 24-month efficacy was 0.28 mm.” Can you describe what this means for the patients using this lens and for the efficacy of the lens?

Mark Bullimore, MCOptom, PhD, FAAO

Dr. Bullimore: Let’s take the two-year efficacy, which you correctly said was 0.28 mm. What that means is that compared to a group of children wearing spectacle lenses, you would expect the elongation to be 0.28 mm or about 0.3 mm less in children wearing the Euclid OrthoK lenses compared to regular or traditional spectacles. The Euclid OrthoK lens slows axial elongation by about 0.3 mm over two years. 

Now, interestingly, that may be the sort of benchmark that the FDA’s Division of Ophthalmic, Neurological and Ear, Nose and Throat Devices might seek for these kinds of devices, and it’s very similar to the slowing of axial elongation observed in the three-year MiSight clinical trial. So, the Euclid OrthoK lens, both compared to that alternative option, and indeed, compared to other options, is effective. Having a whole raft of data supporting that I find quite compelling; it’s thousands of patients here.

RMM/Sailer: Are there other results from all these years of studies that are significant that should be called out?

Dr. Bullimore: One thing that’s unfortunate about all these papers is that relatively few of them talk about the safety of the lens. Those that do didn’t find any issues. Of course, we know from my work and that of others that overnight OrthoK is a safe and acceptable lens modality for children to wear. There is a small amount of risk of corneal infections, but the fact that the lens has been approved for 20 years and indeed was the subject of a post-market safety study, suggests that the level of safety is acceptable. 

The other thing that was interesting in our research was the CAMP study, which was recently published in Optometry and Vision Science. This was a retrospective study based on patients seen at Treehouse Eyes in previous years. Among those patients, there are a lot of children who were fitted with the Euclid OrthoK lens, so that represented an additional set of data on which we could assess the efficacy of the lens. Now, because this was a retrospective study and there wasn’t a control group, we had to use a virtual control group. But, intriguingly, the two-year efficacy in that cohort of patients wearing the Euclid lens was virtually identical to what was found in the 12 papers that were published exclusively on East Asian children. It’s nice to see that the efficacy in U.S. children seems to be the same as the efficacy in East Asian children. That fits into the report that Dr. Noel Brennan and I published earlier in the year. The efficacy, when you talk about millimeters or diopters, is independent or unaffected by the race of the child.

RMM/Sailer: That is very interesting, and it’s good to have corroboration out there. Back to the main results of the study, slowing the axial length growth, can you describe why axial length is important and why it’s the preferred method of measuring myopia progression?

Dr. Bullimore: Axial length correlates very closely with myopia progression. When you look at studies where they can measure both axial length and refractive error, you see a very high correlation. So, if you look at some of the spectacle studies, the MiSight clinical trial for example, you see a good correlation. With OrthoK you’re temporarily reducing myopia. So, you can no longer use refractive error as an outcome measure. You must rely on axial length. So, none of these 37 papers provide any data on slowing myopia progression based on refractive error because they didn’t want to wash the children out of their lenses to get a refractive error measurement. As my colleagues and I have advocated, axial length is the preferred way of assessing myopia progression.

There are other reasons for that. The instrumentation is astonishing. Your publication featured a number of articles on this. The tools we have available to us, these modern optical biometers, have exquisite precision, and they’re valuable tools for monitoring a patient over time. The other thing is visual impairment is related to or affected by both axial length and refractive error. However, when you allow both to compete in a statistical model, axial length is significant, but myopic refractive error is no longer significant. That makes sense because when you think about eye diseases and visual impairment, it’s not the thickness of the lenses or the weight of the glasses that is causing the visual impairment. It’s the chronic and progressive stretching of the eyeball that leads to these unfortunate conditions we see in older patients.

RMM/Sailer: Yes, we agree on axial length, and we cover biometers all the time. We’ve called axial length the gold standard. Thanks for some insight into that. So, you were able to do this study because of the volume of research on the Euclid lenses. How does the volume of research on Euclid lenses compare to other optical devices or other myopia management modalities as well as to other OrthoK brands? 

Dr. Bullimore: In terms of optical devices, OrthoK is by far the most researched modality. Spectacle lenses would probably come in second, but spectacle lenses are very heterogeneous. You can go back to the ‘50s and ‘60s and find papers on bifocals. Then you can find papers on progressive lenses and early designs with radial progressive power. Of course, the latest generation of specially designed spectacle lenses seem to be the most effective, where you have lenslets in the periphery. But when you look at OrthoK papers that look at axial elongation, it’s way ahead of soft lenses. Again, with soft lenses, you’ve got a multitude of different designs that make comparisons difficult.

Within the OrthoK market, other designs were identified in our search, but the Euclid lens was studied or published about more than twice as much as the second nearest lens. Actually, if you add the lenses that were number two, number three, number four, they still don’t come close to the number of papers that have been published on the Euclid lens, particularly when it comes to myopia progression.

RMM/Sailer: With the release of this study that you did, how does its publication impact real world practitioners?

Dr. Bullimore: If we take the U.S., the Euclid OrthoK lens is approved for the temporary reduction of myopia. It is not approved for the slowing of myopia progression or the slowing of axial elongation. Indeed, in the U.S., no OrthoK lens is approved currently for slowing the progression of myopia. They are all approved for the temporary reduction of myopia. Because of that, it’s difficult for the practitioner to find information on the efficacy of the lens for myopia progression. In the case of the MiSight lens, there’s product information that’s included with the lenses. It’s available for practitioners on the FDA site, and they can see how effective the lens is. So, in the case of the Euclid OrthoK lenses as well as other OrthoK lenses, my impression is that most of the patients who are fitted with the lens are fitted in an off-label indication in the U.S. They’re fitted by the practitioner for myopia progression, even though the lens is not approved in the U.S. for that indication. Now, with the publication of our recent paper, a practitioner has access to a huge amount of information on the efficacy of the Euclid OrthoK lens that they would’ve had to search around for themselves and interpret using their own resources. We’ve done that for them, and hopefully it proves very useful to them.

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