Recently, I presented the following case report to a group of colleagues: Asian girl, 9 years old, referred to you for myopia control. Based on the reference notes, she is OD -4.50/-0.75 x 180 and OS -4.25/-0.50 x 10, who had progressed by 1D compared to a year before. And I asked: what would you do? Not surprisingly, 100% of them would consider implementing a myopia control strategy and expectedly, all of them would start with Ortho-K (OK). Would you do the same?
For me, I would need more information before jumping in one strategy versus another, based only on the myopia progression and the script. Here is my thinking process to define a strategy for myopia control, which I have described in Contact Lens Spectrum:
- Age: 9 years old. Becoming a myope before the age of 10 leads to higher risk of faster progression compared to older children, so a strategy should be implemented to target the highest percentage of myopia control.1
- Long-term perspective: progression, for a child of Asian descent, is expected to end at 22 years old, which suggests a minimum of 10 years of progression ahead.2 She has a history of -1D/year myopia progression. Extrapolating likely progression data from Donovan et al3 indicates that if this child were to progress as an average child of her ethnicity, her myopia could double, and she’s already progressed more in the past year than average. To avoid this child increasing to high myopia, an effective myopia control strategy will be needed.
- Background: This patient has 2 parents and an older brother with high myopia, so her genetic background supports more aggressive therapy.4
- Outdoor activities: none, which is crucial to include in the management protocol.5
- Near-work: screen time greater than 2 hours per day, so lifestyle management will be addressed.6
- Refraction: -4.50D – there are suggestions that lower myopia may be better controlled with soft lenses or highly customized OK lenses with smaller treatment zones. At -4.50, I would consider OK – expect to generate at least 4.5 D of peripheral ‘add’ power,7 although how this translates into a change in actual accommodative response has yet to be determined. Anecdotal reports and theories suggest that lower myopia may be better controlled with soft lenses, through achieving a higher ‘add’ power than through OK. There are also suggestions that smaller treatment zones in OK may increase the shift in relative peripheral myopia. As described below, smaller pupil sizes show a lower myopia control effect with OK8 so perhaps, by extension, a smaller OK treatment zone may give a better myopia control effect, although this has not been published yet in the peer reviewed literature. Customizing OK lens parameters to achieve better myopia control – whether this can be achieved, and how – is another topic to itself.
- Corneal topography: the cornea is regular in shape, with no significant astigmatism. In line with the lens choice strategy described in my Contact Lens Spectrum paper, a corneal eccentricity (flattest meridian) of 0.7 means I expect an OK myopia correction of 4.5 D maximum (= ecc/0.2 +1D), which fits with the refractive outcome desired.
- Pupil diameter: 3.5 mm. This is a very small pupil. Orthokeratology may give good acuity but will not give as strong a myopia control effect with such a small pupil. To the contrary, OK treatment with such a small pupil may contribute to increase axial length and myopia – Chen et al8 found that OK wearing children with below average pupil sizes (less than 6.43mm) showed more progression than children with larger pupils, and while the authors didn’t analyse it, the OK small pupil group appeared to progress more quickly than the single vision glasses group. Pupil size had no effect in single vision glasses, indicating the importance of achieving a good OK treatment and matching it to the right patient characteristics for best outcomes. For this patient, we may consider adding atropine to increase pupil size or to select soft multifocal lenses as the modality of choice.
- Axial length: 25.5 mm - We now know that axial length over 26 mm increases significantly the risk of visual impairment over a lifetime.9 We have to be very aggressive here in the control strategy, considering that progressing patients generally show axial growth of -0.1 to 0.3mm per year.1
In summary, this case may seem to be a straightforward choice to prescribe OrthoK lenses. With the big picture in mind, though, we now realize that we have to implement an aggressive control strategy. Lenses alone and visual environment changes will not reach this level. Atropine should be considered as adjunct therapy to meet this demand. Atropine will also help us to increase pupil size and then OK may be considered. Otherwise, with a small pupil, OK may not halt progression, except with an effective customized design.
I explained the strategy to the parents who endorsed it. They were also advised that any progression may bring the need to wear regular glasses during the day. In fact, based on corneal eccentricity, it would be hazardous to try to correct more than -4.5D. We may create corneal erosions, and open the door to infections, and perhaps corneal ulceration. Partial OK is as effective as full OK.10 Practitioners have to make a differentiation between strategies for myopia correction and myopia control. As for the latter, I limit myself to what cornea can give me and I rarely go over -4D to keep myself on the safe side.
The patient will be closely followed up and atropine dosage will be modified as needed if progression exceeds what is expected.
In conclusion, this case report, simple to begin with, reminds us that myopia control strategy should never be just ‘ok.’ We have to get the big picture.
Langis Michaud is a full professor and chief of the contact lens department at École d’optométrie de l’Université de Montréal in Canada. In his spare time he plays golf and dreams of one day running a winery.