Myopia Control Was Always About Contrast, Not Correction

A clinician who's been fitting OrthoK since the early 90s traces the signal-contrast theory that explains everything from lens design to Stellest 2.0.

In the early 1990s, I had eight-year-olds in my exam chair who were more nearsighted than their parents had been after graduate school. There were no myopia control specialists yet — that category didn't exist — so we did what clinicians do: we watched the data and started experimenting. What we found eventually explained not just why OrthoK worked, but why it sometimes didn't, and why thirty years later, a French lens company just proved the same principle holds with 90% efficacy in a controlled trial. My practice was in the western suburbs of Chicago, and the pattern was unmistakable: Chinese families, among the highest-risk groups for early-onset myopia, were driving the trend.(1)

The Reverse Curve Revelation: Elevation Contrast Is Everything

What we learned back then was that the present technologies for correcting these higher degrees of correction in the form of optical interventions were inadequate. The biggest take-home was that unless we created enough elevation causing contrast in our designs from the reverse curve zones our patients advanced at alarming rates still.

In fact, because of this we actually discovered that there was a certain minimum elevation required in this that was attained on its own if the patient already had mid to high myopia (4–6 D). These patients with standard OrthoK designs showed little change over time in their prescription.(2)

More Power, Less Progression: Eddie Chow's Breakthrough Design

So the game was on to discover just what it might take to design OrthoK lenses for low myopes that could accomplish that stability. Eddie Chow did the groundbreaking work here first by demonstrating this stability in a five-year retrospective study and then demonstrating that by introducing increased Jessen power with positive asphericity in the design on how to accomplish this goal. Eddie’s new design was met by skepticism but proved extremely effective in slowing axial length growth.(3)

Why the Brain Chooses Neither Signal

We learned that increasing the difference between signals that fall on the central posterior pole and those predominantly myopic defocus mid-peripheral signals, if sufficiently different, resulted in stability in AL. The theory goes that given two disparate signals, particularly if one of those is myopic defocus, the brain/eye will choose neither as a growth signal. This explains why our worst-case signal contrast — that of central fovea corrected to 20/20 by minus single vision lenses and the resulting hyperopic mid-peripheral blur — leads to rapid AL growth as the brain/eye attempts to resolve the hyperopic defocus by growing in AL. Myopic defocus in the mid-periphery is a non-resolvable dilemma for the brain/eye visual system.(4)

"Given two disparate signals — particularly if one is myopic defocus — the brain/eye will choose neither as a growth signal"

Stellest 2.0 and HALT Technology: 30 Years Later, Same Physics

Now advance the clock some twenty years and the groundbreaking Stellest design with HALT technology is doing its own fine-tuning to accomplish the goal of stabilizing axial length with its new 2.0 design. They did this by increasing the power and asphericity of its lenslets to accomplish the goal of roughly a 50% additional slowing of AL growth — and it proved effective for ninety percent of the subjects! The only hesitancy I have is: when will it be available for doctors to prescribe here in the US?(5)

(1) Longitudinal myopia progression in Chinese children — PMC https://pmc.ncbi.nlm.nih.gov/articles/PMC12357225/

(2) Axial length stability with standard OrthoK designs — PMC https://pmc.ncbi.nlm.nih.gov/articles/PMC11422374/

(3) Chow: Increased Jessen factor in OrthoK for low myopes — YUMPU/Contact Lens Spectrum, Jul 2017 https://www.yumpu.com/en/document/view/59210434/jul-2017

(4) Peripheral defocus and emmetropization signals — PMC https://pmc.ncbi.nlm.nih.gov/articles/PMC11044358/

(5) Advancing Myopia Management with Stellest 2.0 — Review of Myopia Management https://reviewofmm.com/advancing-myopia-management-with-essilor-stellest-2-0-lenses/

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