We are at an interesting crossroads in our understanding of myopia: Most of us believe that the incidence is increasing throughout the world and particularly in Asian countries.
I get the sense that, while there has been some concession toward environment playing a role, the thought that near work could have anything to do with myopia progression is just so offensive to some that any other theory that emerges is greeted with much enthusiasm.
This seems to be the case for the findings indicating a correlation between hours spent outdoors and a delayed age of onset (Rose et al.). A link between time outdoors and the rate of progression of myopia is either nonexistent or much weaker. Nevertheless, there is much excitement about increasing outdoor exposure, mandating changes in human behavior, changing school systems, building classrooms out of glass and trying to convince academically minded parents to send their kids outside for 2 hours instead of having them work on their schoolwork.
A bigger question remains: What do we do about someone with myopia? Multiple studies strongly suggest three effective treatments for myopia progression – atropine, orthokeratology (ortho-K) and bifocal contact lenses, with bifocal glasses helpful for some.
Recent studies using meta-analysis suggest that atropine might be the most effective treatment, and there seems to be increasing enthusiasm for using 0.01% atropine because of apparent effectiveness, demonstrated low incidence of side effects and less of a rebound phenomenon (Chia et al.). This enthusiasm seems to be misplaced, given that there is no current evidence that 0.01% has any control over axial length.
Jeffrey Cooper published an analysis of atropine dosing strategies and concluded that 0.02% is the highest dose that would be associated with minimal side effects. Given that the myopia control effect found with atropine appears to be dose-related, it would be prudent to prescribe the highest, well-tolerated dose. Despite the likely efficacy of atropine treatments, it is destined to forever be an off-label treatment, making parents a bit nervous and requiring a compounding pharmacy with the attendant high cost and inconvenience.
There is also a lot of enthusiasm about ortho-K for myopia control, for the obvious advantages of clear daytime vision without lenses and an average, demonstrated 40% to 50% control of myopia progression (Gifford et al.) If one wants to practice evidence-based optometry, it is prudent to keep in mind that the average myopia control effect found with six clinical trials is 48% (Turpin). Cautious practitioners must also advise patients and parents that the best available evidence from clinical trials indicates that the risks of microbial keratitis with ortho-K are the same as with any overnight lens.
There are hints from these studies and predictions based on the presumed mechanism for control with ortho-K that the resulting effect is less for lower levels of myopia and greater for higher levels of myopia.
Interestingly, the average myopia control effect with bifocal contact lenses from five clinical trials is the exact same: 48% (Turpin). What I find interesting about this average percentage is that ortho-K is routinely described as more effective than bifocal contact lenses for myopia control. Individual practitioners may find better control than the studies suggest, perhaps due to the particular design used or, perhaps in the case of ortho-K, due to the particular mix of refractive errors treated, with higher levels of myopia showing greater control than the averages in the clinical trials.
It is unavoidable with ortho-K treatment that higher levels of treated myopia will generate higher levels of peripheral plus power, so a clinical trial of ortho-K might result in greater control for higher myopes. In most clinical trials of bifocal contact lenses, the chosen add powers are the same for all subjects and typically in the +1.50 D to +2.50 D range. The lone exception to these trials was our CONTROL study (Aller et al.), where the add power was chosen specifically to neutralize the subject’s eso fixation disparity at near. This study also enrolled progressing myopes and found an 80% control of axial elongation as compared to single vision soft contact lenses.
Perhaps I get a bit annoyed when these findings and the other bifocal soft lens studies are ignored by those who say that ortho-K is great and bifocal contact lenses are less effective. It would be great if there were a randomized clinical trial that showed that ortho-K controlled myopia better than what the current trials have reported. Until that day, the available research does not support any statement that ortho-K controls myopia better than bifocal contact lenses.
Optometry is uniquely suited – and I would argue ethically and professionally compelled – to take appropriate steps, supported by the available literature, to effectively treat myopia progression. Ortho-K delivers excellent vision and effective myopia control, but it accounts for only 2% of contact lens fits according to a recent international study (Morgan et al.). These practitioners have invested the time to become skilled in the art and have invested significant resources to acquire the necessary equipment to provide this service.
Noel Brennan has argued that a mere 33% reduction in myopia progression would reduce the level of high myopia (more than 5.00 D) by 73%, and Brien Holden has shown that a 50% reduction in myopia progression would virtually eliminate the existence of myopia of more than -6.00 D. Every optometrist and ophthalmologist who takes myopia seriously can easily achieve myopia control in these ranges using a mix of bifocal glasses, atropine, bifocal contact lenses and ortho-K.
- Aller TA, et al. Optom Vis Sci. 2016;doi:10.1097/OPX.0000000000000808.
- Brennan NA. Cont Lens Anterior Eye. 2012;doi:http://dx.doi.org/10.1016/j.clae.2012.08.046.
- Chia A, et al. Ophthalmology. 2012;doi:10.1016/j.ophtha.2011.07.031.
- Cooper J, et al. Optom Vis Sci. 2013;doi:10.1097/OPX.0000000000000037.
- Gifford P, et al. Optom Vis Sci. 2016;doi:10.1097/OPX.0000000000000762.
- Holden B, et al. Eye (Lond). 2014;doi:10.1038/eye.2013.256.
- Morgan PB WC, Tranoudis DO. International contact lens prescribing in 2015. Contact Lens Spectrum. 2015;31:24-9.
- Rose KA, et al. Ophthalmology. 2008;doi:10.1016/j.ophtha.2007.12.019.
- Turpin S. Assessment of three multifocal soft lens designs for myopia control: Pacific University; 2016. http://commons.pacificu.edu/opt/19. Posted May 12, 2016. Accessed Dec. 20, 2016.
- For more information:
- Thomas Aller, OD, FBCLA, of San Bruno, Calif., is a senior project scientist for the Vision Cooperative Research Centre. He can be reached at firstname.lastname@example.org.
Disclosure: Aller is a member of the Treehouse Eyes board of advisors and a consultant for the Myopia Control Programme at the Brien Holden Vision Institute.