Orthokeratology for anisometropia

The standard of care for childhood myopia has changed – we now prescribe visual correction as well as manage it by reducing the risk of progression. Contact lenses are always a better choice for patients with anisometropia as they can equalize retinal image size and improve binocular vision.¹ Here is a great case shared in the Myopia Profile Facebook community, involving an anisometrope managed with ortho-k lenses.

ortho-k is the only myopia control intervention which has evidence for control of myopic anisometropia: both monocular myopia and bilateral anisomyopia. One meta-analysis published in late 2021 evaluated 10 studies, most of which were retrospective, and found significant effects for ortho-k’s ability to slow axial elongation to a greater effect in the more myopic eye.² 

In cases of monocular myopia, eye growth in the myopic eye was slowed by a mean of 0.27mm over one year and 0.17mm over two years compared to the emmetropic eye. In cases of bilateral anisomyopia, the more myopic eye showed slower growth by a mean of 0.06mm over one year and 0.13mm over two years across the various studies.² All of these studies were conducted in the region of Asia. None were randomized controlled trials – this would involve comparison to another type of treatment for anisometropic myopes which is not ortho-k. This means that an ‘increased efficacy’ effect can only be expressed in comparison to the other eye of these anisometropic myopes.

The mechanism for this is unknown. It has been shown that higher baseline myopia can be associated with slower axial elongation in ortho-k wearers.^3,4 This does not mean ortho-k is less effective for lower myopes – those with higher myopia may be older or have other factors related to myopia stability, and not all studies have found this same result. The significant optical changes induced by ortho-k, which would be larger for a more myopic treatment, could drive this beneficial effect on anisomyopia.³

Ortho-k has a long history of research in myopia control, indicating robust efficacy and safety outcomes.5 In this case, the patient exhibited stability of axial length over a year wearing ortho-k in her right, myopic eye, while at the same time her left, emmetropic eye showed elongation of 0.1mm per 3 months, and progression into myopia. Fortunately, the eye care practitioner acted quickly to fit ortho-k to the patient’s newly myopic left eye, so she can benefit from myopia control for this eye as well. 

1. Anisometropia is better to treated with contact lenses than spectacles.
2. Ortho-k lenses are an ideal choice for myopia management with a strong evidence base, and is the only treatment which shows evidence for slowing axial elongation in the more myopic eye of patients with anisometropia.