Myopia control is much more than just a new modality for our contact lens practice – it is a shift in paradigm. We may be converting our practices from simply correcting ametropia and servicing our patients’ refractive needs to treating them in a therapeutic way, preventing or minimizing myopic retinopathy and potentially changing lives. We actually may need new terminology for the myope - somewhere in between a patient and a customer – to fully grasp and define the concept of myopia control.
NCC conference 2016
I remember at our 2012 Dutch contact lens conference, there was a substantial amount of attention regarding myopia control and contact lenses. We are now gearing up for our 2016 meeting in March…and again, there has been a lot of interest in this topic. But – from a practice standpoint, what has changed in the last four years? Are many of us actively promoting or at least informing about myopia and myopia control to our patients (customers, or whatever)?
The latter is a bit of a rhetorical question – not much is done yet in most practices. Part of the problem is that myopia control is complex. There are the ‘general’ numbers showing us about 50% slowing of myopia progression with orthokeratology, and numbers near to that with soft dual-focus options. But what does an average mean to the patient you have in your chair at this very moment?
Why is myopia control so complex? It seems that when you start digging deeper, it only becomes more complex. As an example: peripheral retinal defocus seems pretty straightforward. But the retinal profile is not a sphere, an ellipse or any other simple shape that our minds can grasp. We would need a complex Zernike polynomial (or more complex description) to describe the shape. But what’s worse is that it is most likely different for every individual. So if you would like to provide some sort of optical peripheral defocus to control the peripheral retina, you would actually need to know this shape in advance. And the optical pattern that needs to be applied may be different for different patients, too, depending on the current level of myopia, age, rate of progression etc.
Moreover, we need to get our act together on the lens fit, especially because we are working with kids. But when it comes to soft lens fitting, we don’t quite have full control over it. In addition, unlike when fitting corneal GP lenses and orthokeratology, we don’t have adequate technology in our practices to measure the ocular surface shape around and beyond the corneal borders. The reason why this may become relevant is that when a soft lens is placed on the ocular surface, a certain amount of flexure will take place. But the amount of flexure is unclear. Our studies at Maastricht University and Pacific University show that this can be quite substantial. If there is an excessive amount of difference between the sagittal height of the lens and that of the ocular surface (over the same chord), such as 400 microns – then this can have a substantial (negative) effect on lens flexure, on the optical performance of the lens on-eye – and potentially on the myopia controlling efficacy of that lens.
Another thing to consider is soft lens decentration. As it has become clear from scleral lens fitting, the anterior scleral shape is not symmetrical. In short: the nasal area of the anterior ocular surface is flatter compared to most other parts, and in particular it is flatter than the temporal side of the eyeball beyond the corneal borders. Hence, in both scleral and soft lens fitting, this may result in some sort of temporal decentration when the lens is placed on the eye. This decentration comes in addition to the negative influence of the geometrical center of the eye versus the line-of-sight, which often already results in a temporal offset. If the central optics of the myopia control lens are too much out of line with the line-of-sight – this again can have a potential negative effect on the myopia control efficacy.
What all this means is that we will likely have to customize lenses for myopia control. Because ‘substantial amounts’ of plus in the periphery seem to be needed to take advantage of the myopia control effect, we may need to consider what lens modality would work best. For a young 9-year-old with low myopia, let’s say 1.00D of myopia, what would be the best option? Many would consider orthokeratology, as it has proven to be one of the most robust myopia control modalities. But a standard orthokeratology lens may provide only +1.00D of peripheral defocus. That may not be enough. A dual-focus soft lens at this point may be the best option for that patient. If the patient progresses (to a lesser degree, presumably) to a higher level of myopia, then orthokeratology may be a good option later in life.
To reiterate – myopia control is complex, and this is just the beginning. But for me, at least one thing is clear: for myopia control to be successful, it needs to be performed with a customized lens geared toward the individual anatomical features and refractive profile of the myope. In Dutch we have a saying ‘In Optima Forma,’ which means ‘to be perfect’ or ‘at its best’ form or shape. For myopia control to be effective, it needs to be ‘In Optica Forma’ for me. The optics should be right, and the form or shape should be right too. Most likely, optimized front surfaces (different optical profiles) and back surfaces (to align the lens best with the ocular surface and to potentially prevent decentration) would provide the best results. And that would actually be totally in sync with the current 3D-printing era we live in. I look forward to it! The time is right. The future of our contact lens practices may be much more ‘customized’ than currently is the case.
Eef is an educator and researcher. He is adjunct assistant Professor at Pacific University College of Optometry (Oregon, USA, University of Maastricht associate researcher and adjunct Professor at the University of Montreal University College of Optometry (CA).