When a child is only myopic in one eye, it is known as unilateral myopic ametropia. This is defined as the specific refractive state where an unequivocally myopic eye is paired with a 'plano' (spherical equivalent refraction +/-0.25D) companion eye.1 AS shared this case on the Myopia Profile Facebook community, looking for the best treatment strategy for managing unilateral myopia.
What is unilateral myopic ametropia?
Unilateral myopia typically manifests in the pre-teens and has a marked female gender bias. The refractive progression trend of the myopic eye in a unilateral myope is generally similar to that of a bilateral myope. The emmetropic eye is also expected to have myopia progression in the future.2
What are the treatment options?
Spectacles or contact lenses for unilateral myopia?
Most of the discussion involved fitting contact lenses for this patient. Contact lenses provide a beneficial option for correcting anisometropia as well as a readily available, effective option for myopia control.
The contact lens options mentioned include orthokeratology lenses (OrthoK lenses), multifocal soft contact lenses (e.g. NaturalVue) and MiSight. Single vision contact lenses aren’t mentioned, presumably because it wouldn’t make sense to use single vision lenses when a patient is already being fitted with contact lenses.
The literature supports some form of myopia control contact lens treatment to the myopic eye. Chen et al3 and Tsai et al4 showed that there was less axial elongation on the myopic eye that received OrthoK lens treatment compared to the emmetropic eye in unilateral myopia. Some of the commenters also described success in monocular OrthoK fitting.
The new generation of myopia controlling spectacles have similar efficacy to these contact lens options, although are not yet as widely available. These could be an option for very low-risk myopia control of a pre-myopic eye, where a close-to-plano refractive power is accessible.
Atropine for unilateral myopia?
A recent study compared OrthoK to atropine 0.01% and 0.05% in anisometropic myopes (although these were not necessarily unilateral myopes) and found that OrthoK was most effective at reducing the inter-eye axial length difference. The study didn't have a control group, but in comparison, OrthoK was also the most effective intervention and the next most effective was 0.05% atropine.5
Monocular versus binocular contact lens fitting?
As described, there is evidence for orthokeratology's efficacy in unilateral myopia control. Although the studies have not been undertaken, it is logical to consider soft myopia controlling contact lenses could provide a similar benefit.
JAS raised an interesting idea of fitting both eyes with a multifocal ('MF' or 'MFSCL') or myopia controlling soft contact lens in order to delay myopia onset in the emmetropic eye. Following this, there was some discussion about monocular versus binocular fitting, with commenters raising concerns about visual adaptation to monocular myopia controlling contact lens wear. Other commenters suggested this could be alleviated with an appropriate over-refraction.
There are no studies investigating or directly comparing adaptation between myopia controlling soft contact lens designs to make a recommendation as to which may be easiest to pursue in a monocular fitting. Depending on the child’s risk factors, you may find yourself wanting to make preventative recommendations for the emmetropic eye, although the risk-to-benefit balance is more difficult for an emmetropic eye where vision correction is not required.
The role of vision therapy
JD makes a good point here that the anisometropia needs full correction before attempting to normalize binocular vision function. This patient has shown accommodative issues, which may or may not alter with vision correction. Whilst it makes intrinsic sense to normalize binocular vision function wherever possible, to support comfortable near vision, there isn't direct evidence available on how improving binocular vision disorders relates to myopia progression. One study applied accommodative facility training to all myopes as a myopia control intervention using a +2.00D/-2.00D flipper at 40 cm for 18 minutes per day for up to 6 weeks. The study did find that higher accommodative lag and AC/A ratio was associated with more myopia progression, and that accommodative facility improved in the short-term for those who underwent training, but over the 24 month study there was no treatment effect of the accommodative facility training.6 This does not necessarily indicate a lack of impact for patients with abnormal accommodative facility, rather no effect when applied to all myopes.
Take home messages:
- Consider contact lenses for managing unilateral myopia, given their benefits for correcting and controlling myopia. A larger degree of anisometropia would tip the scales even further in favour of contact lenses over spectacles.
- Orthokeratology is the only treatment with evidence for efficacy in unilateral myopia control and reduction of anisometropia. This could potentially be extrapolated to soft myopia controlling contact lens interventions, although monocular versus binocular visual adaptation may need consideration.
Further reading on unilateral and anisometropic myopia
- Pointer JS, Gilmartin B. Clinical characteristics of unilateral myopic anisometropia in a juvenile optometric practice population. Ophthalmic and Physiological Optics. 2004 Sep;24(5):458-63. (link)
- Chen Z, Zhou J, Qu X, Zhou X, Xue F, Group SO. Effects of orthokeratology on axial length growth in myopic anisometropes. Contact Lens and Anterior Eye. 2018 Jun 1;41(3):263-6. (link)
- Tsai WS, Wang JH, Lee YC, Chiu CJ. Assessing the change of anisometropia in unilateral myopic children receiving monocular orthokeratology treatment. Journal of the Formosan Medical Association. 2019 Jul 1;118(7):1122-8. (link)
- Fu AC, Qin J, Rong JB, Ji N, Wang WQ, Zhao BX, Lyu Y. Effects of orthokeratology lens on axial length elongation in unilateral myopia and bilateral myopia with anisometropia children. Contact Lens and Anterior Eye. 2020 Feb 1;43(1):73-7.(link)
- Tsai WS, Wang JH, Chiu CJ. A comparative study of orthokeratology and low-dose atropine for the treatment of anisomyopia in children. Scientific Reports. 2020 Aug 25;10(1):1-8. (link)
- Price H, Allen PM, Radhakrishnan H, Calver R, Rae S, Theagarayan B, Sailoganathan A, O'Leary DJ. The Cambridge Anti-myopia Study: variables associated with myopia progression. Optom Vis Sci. 2013 Nov;90(11):1274-83. (link)