August 3, 2026
By Kevin Chan, OD, MS, FAAO, FBCLA, IACMM
Image generated with AI
How do you typically deal with information that is seemingly not aligned, or in conflict with, your long-ingrained beliefs or perceptions? Are you primed to agree with what you have already believed in, while being more likely to refute opposing views?
Responses can be mixed or controversial because they can also inadvertently trigger self-doubt or visceral reactions when their belief and perception is seemingly upended or challenged by a new, foreign force.
One thing I have learned throughout my career is to NOT say “never” to possibilities. In fact, “never” is the antithesis of possibility.
The central proposition of the well-established peripheral defocus theory1 was undoubtedly set as bedrock in myopia research. That is, peripheral hyperopic defocus was hypothesized to promote axial elongation. On the other hand, the prevailing force of peripheral myopic defocus aims to attenuate axial length growth by deliberately generating blur at mid-periphery of the retina.
Nevertheless, the notion of peripheral defocus is often intertwined with the enigma of optic zone size (OZ) and peripheral refraction profile (PRP). This has fundamentally become a focal point of discussion in myopia research and practical lens design. That said, it is worth noting that peripheral refraction also varies by eccentricity, meridian, accommodation, pupil diameter, lens centration, frame fit, gaze angle and instrumentation.
When Evidence Meets Doubt and Uncertainty
In the latest research on the topic of corneal refractive powers derived by orthokeratology and myopia control treatment efficacy, Li et al.2 seemingly drew a uniquely opposing and provocative theory for us to ponder. For me, this has fundamentally challenged the emerging evidence and belief that “the smaller the OZ size, the better the result would be.” (This research will be discussed in depth in an upcoming research review.)
Here comes the juncture for us—both cognitively and intellectually. Do we have enough evidence to irrevocably support or refute one of the most enlightening, yet also controversial, subjects in shaping the current and next frontier of myopia control? The truth is, there isn’t. Not yet.
It is important to understand that clinical plausibility is not equivalent to clinical certainty. The current literature in favor or support of OZ size and PRP denote an important mechanistic construct, but not as a stand-alone diagnostic, prognostic or therapeutic endpoint.
Processing Data
The question isn’t simply about new research; but more about how new data should be processed to help us rationalize or diversify this seemingly flawless framework. Interestingly, according to the discovery by Li et al, if efficacy differences were not derived from a small treatment zone size alone, what other factors come into play?
Surprisingly, it was reported that clinical efficacy is ultimately derived from the RATE OF CHANGE of the power profile, rather than the specifications of the manufactured optic zone or the peak corneal power generated.
Putting this conundrum into a novel lens perspective—two lenses of the same manufactured optic zone and maximum corneal power can exhibit different resultant corneal power ranges and retinal images based on how the corneal profiles among different curvatures are manipulated. The ultimate clinical effects are likely a composite of peripheral defocus, simultaneous myopic defocus, retinal contrast, aberration distribution, pupil size, accommodation, gaze behavior and adherence as well.
Practice Amid Theories Vary with Reality
This reinforces a crucial point: clinical heterogeneity still exists across interventions and trials despite the most rigorous and stringent effort. Practical applications of myopia management have morphed beyond the “all-or-none” theoretical optics alone and now warrant personalized frameworks and strategies.
In essence, clinical success should no longer be founded by a single theoretical argument, but rather how we embrace and rationalize both prevailing and conflicting data in harmony.
So, is this the time to shift the dogmatic idea of “peripheral plus” generated by optical interventions as a single, absolute entity to a dynamic, multifaceted thinking of “power and contrast management?” Notably, this continuum of thinking likely stems from the map types used, the location sampled and whether the clinician is evaluating shape, local curvature or refractive power–all in sync with each other. In this sense, while the final verdict is yet to be finalized, small optic zone size no longer unilaterally equates to better treatment efficacy. By the same token, peripheral corneal power should not be perceived and interpreted interchangeably as peripheral retinal refraction. Just as the old adage said, “What you reap isn’t always what you sow.”
The Virtue of Being Doubtful in Clinical Practice
Staying cautiously doubtful and inquisitive isn’t inherently a bad attribute; rather, it is an indispensable aspect of quality research. We should continue to allow and embrace constructive criticisms and controversies to help us stay grounded and open-minded for the truth. I strongly believe that research on OZ and PRP will continue to thrive because it helps optimize lens design and enables future individualized treatment algorithms and strategies. Nonetheless, clinicians should avoid fixating on a single entity as a surrogate of clinical success.
Parents and patients do not simply have to hear a bolder message, but also a carefully weighted and cautiously crafted interpretation and patient counseling. Contrary to what most believe, patients and families would likely feel more assured by hearing “I don’t have all the answers, but…” than “This is risk-free and absolutely the way to go.” It indeed epitomizes a patient-driven intervention that is specifically curated with them and for them.
Remember that hypotheses are key to driving research endeavors, but we also should not let hypotheses be the antithesis or a “blind spot” for the greater good either.
References:
- Smith EL 3rd. Prentice Award Lecture 2010: A case for peripheral optical treatment strategies for myopia. Optom Vis Sci. 2011 Sep;88(9):1029-44. doi: 10.1097/OPX.0b013e3182279cfa. PMID: 21747306; PMCID: PMC3371664.
- Li N, Jiang W, Wang N, Cai Z, Du B, Lin W, Wei R. Comparing myopia control efficacy and corneal power changes in children wearing corneal refractive therapy (CRT) and vision shaping treatment (VST) orthokeratology lenses with smaller back optic zone diameters. Photodiagnosis Photodyn Ther. 2026 Jun;59:105482. doi: 10.1016/j.pdpdt.2026.105482. Epub 2026 Apr 17. PMID: 42001921.
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