STABLE REFRACTION doesn’t always mean stable myopia. This has never been truer than when monitoring orthokeratology (ortho-k). The nature of ortho-k leads to variations in refractive data that are a moving target (dependent on factors such as wear time and what time of day).

Understanding the Numbers

Axial length represents an objective measurement of eye length from the anterior cornea to the fovea. A small amount of normal physiologic growth reflects coordinated enlargement of the globe, including equatorial expansion. In contrast, progressive myopia is characterized by disproportionate axial elongation of the posterior segment, resulting in a more prolate (ovoid) eye shape rather than a spherical one (Atchison et al, 2004).

Understanding normal benchmarks is key to evaluating risk and progression. Untreated myopic children often demonstrate axial elongation approaching or exceeding 0.20 mm per year (Tideman et al, 2018). In contrast, successful myopia control interventions have been shown to reduce axial elongation into the range of approximately 0.10 mm to 0.15 mm per year in treated cohorts (Cho and Cheung, 2012; Walline et al, 2020).

Clinical Pearl: A laminated chairside chart that includes normative data for axial length growth can serve as a useful clinical reference and should be customized to account for both age and ethnicity.

Timing Is Everything

Due to seasonal and diurnal variations in choroidal thickness, fluctuations in axial length measurements are common. For this reason, schedule follow-up visits at the same time of day and account for seasonal variations when interpreting data.

Clinical Pearl:Align axial length measurements with clinical milestones such as initiation of the first ortho-k lens, lens refits, growth spurts, and receipt of a first smartphone or tablet, which often corresponds to increased near work.

From Data to Decision

When axial length measurements are stable relative to expected physiological growth, the decision is easy: continue the current plan. If elongation suggests accelerated growth, review compliance, wear time, and visual hygiene. Evaluate centration and treatment zone size. True progression may necessitate a lens refit, revisiting visual hygiene habits, and adding dual therapy with low-dose atropine.

Clinical Pearl: Do not overreact to a single axial length reading. Look for a sustained trend prior to making a change in the treatment plan.

Communicating Value

Plotting a patient’s axial length on a growth chart (Figure 1) allows the clinician to leverage axial length as a tool to communicate value. This approach highlights the success of slowed growth and reinforces the importance of myopia management. It also demonstrates the level of technology that the practice has invested into its clinical arsenal.

References

1. Atchison DA, Pritchard N, Schmid KL. Eye shape in emmetropia and myopia. Invest Ophthalmol Vis Sci. 2004;45(10):3380-3386. doi:10.1167/iovs.04-0292

2. Tideman JWL, Polling JR, Vingerling JR, et al. Axial length growth and the risk of developing myopia in European children. Acta Ophthalmol. 2018;96(3):301-309. doi:10.1111/aos.13603

3. Cho P, Cheung SW. Retardation of myopia in orthokeratology (ROMIO) study: a 2-year randomized clinical trial. Invest Ophthalmol Vis Sci. 2012;53(11):7077-7085. doi:10.1167/iovs.12-10565

4. Walline JJ, Greiner KL, McVey ME, Jones-Jordan LA; BLINK Study Group. Effect of high add power, medium add power, or single-vision contact lenses on myopia progression in children: the BLINK randomized clinical trial. JAMA. 2020;324(6):571-580. doi:10.1001/jama.2020.10834