This article was originally published in a sponsored newsletter.

Data from myopia studies is exploding, and it can be a challenge to understand and implement findings into clinical practice. While myopia control implies slowing the progression of refractive error change, our mindset as clinicians needs to be focused on changes in axial length. Recent axial length data on emmetropes and on both treated and untreated myopes has shed light on how providers can interpret the efficacy of their selected myopia control methods.¹

As young emmetropes mature through their childhood, components of their optical system change to maintain an emmetropic refractive error through the development years. On average, axial length will change about 0.1mm/year in 6- to 14-year-old emmetropes.¹ During this time, the crystalline lens will thin and flatten in shape to compensate for the axial length change.

There is also data that show a correlation of axial length and height changes to maintain emmetropia.² These changes are considered physiologic in nature and a normal part of a child’s ocular development. As a provider utilizing myopia control in clinical practice, it is important to understand that even emmetropes elongate through childhood.³

The changes that occur to a myopic eye during adolescence are due to the loss of the balance between axial length, lenticular change, and body growth. According to Kearney and colleagues, progressing myopes experience a rate of axial length change that is five times greater per centimeter of height growth, compared to their emmetropic peers.²

In addition, after the onset of near-sightedness, myopic children undergo accelerated year-over-year axial length changes rather than the exponential slowing of change that emmetropes experience.3 This type of eye growth, which is over and above the normal ocular development, has been called pathologic axial lengthening.

Reported rates of axial length change during adolescence can be used to assess the efficacy of our myopia control efforts (see Table 1).³

 When compared to their myopic and emmetropic age groups, a 0.1mm axial length change in an 8-year-old myope shows the current treatment is likely more effective than a 0.1mm change in a 14-year-old using the same therapy.

Another way to utilize this axial length data is alongside reported efficacy rates of myopia control methods. If the rate of an axial length control method is 50%, a target axial length could be set year-over-year based on the child’s age and expected change. This could also help determine whether a child may need single or combination myopia control therapies to reach an acceptable level of yearly growth.

Even with all this data, the risk for ocular pathology related to myopia remains the cumulative axial length change over the child’s life.³ It is important to not become complacent with reaching an emmetropic rate of change, especially in our younger and higher myopes.

I plan to use this data to help me determine when my primary myopia control method is not fully effective and prompt adjusted treatment and understand when max efficacy with monotherapy has been reached to justify adjunct therapy.

References:

1. Mutti DO, Hayes JR, Mitchell GL, et al; CLEERE Study Group. Refractive error, axial length, and relative peripheral refractive error before and after the onset of myopia. Invest Ophthalmol Vis Sci. 2007 Jun;48:2510-2519.
2. Kearney S, Strang NC, Cagnolati B, Gray LS. Change in body height, axial length and refractive status over a four-year period in caucasian children and young adults. J Optom. 2020 Apr-Jun;13:128-136.
3. Chamberlain P, Lazon de la Jara P, Arumugam B, Bullimore MA. Axial length targets for myopia control. Ophthalmic Physiol Opt. 2021 May;41:523-531.