Overnight Orthokeratology for Myopia: What Does the Evidence Say?

Why try to control myopia progression?
Myopia has become increasingly widespread. As previously described, the prevalence of myopia has contributed to it becoming a ‘worldwide public health issue’.1-6 Reports have estimated that almost five billion individuals will suffer from myopia by the year 2050. 1,7 Due to this rampant escalation, practitioners have seen an influx of concern regarding myopia control. Contact lens manufacturers are enhancing lens designs and technologies, and there is an increasing number of educational resources available on the topics of myopia control and management.

Genetics, as well as visual behaviors contribute to myopia progression.8 The amount of time children spend outdoors8,9-14and time committed to near activities15 may also play a role. Myopia is associated with sight-threatening conditions such as cataracts, primary open angle glaucoma, retinal detachments, myopic maculopathy, and choroidal neovascular membranes.14,16-18 The higher the degree of myopia, the greater the risk of these conditions. Therefore, reducing an individual’s myopia progression also reduces the risk of these sight-threatening conditions.

What are the current treatments for controlling myopia?
There are two currently accepted treatments of myopia control: reducing the rate of myopia progression or delaying the onset of myopia.14 Several studies have established that previously accepted methods for myopia control such as under correction of myopia 14,19 single vision gas permeable contact lenses,14,20 and bifocal spectacles,14,21 may now be considered ineffective. The time that children spend outdoors may delay the onset of myopia, but not reduce the rate of myopia progression.11,12,14,22,23

The three most-researched treatment approaches that have validated a reduction in the long-term progression of myopia are orthokeratology, soft distance centered bifocal contact lenses,14,24-26, and antimuscarinic agents (atropine).14,27 Patients and parents must be educated that all treatments for myopia control are considered ‘off label’ as part of their informed consent process since there are currently no FDA approved products available with an indication for myopia control.

While all three of the treatments mentioned above are effective in controlling myopia progression, this brief review will focus only on overnight orthokeratology.

How does orthokeratology treat myopia progression?
Orthokeratology (ortho-k) refers to the use of gas permeable contact lenses, that are worn while asleep and removed upon awakening. They create a temporary change in shape of the cornea to correct for low- to-moderate amounts of myopia and astigmatism. Thus, glasses or contact lenses do not have to be worn during the day.1 While each lens design has its unique proprietary parameters, commonly shared features of commercially available ortho-k lenses include the following: a larger diameter, small treatment zone (optic zone), and a secondary or reverse curve steeper than the base curve.8 Ortho-k induces peripheral myopic defocus along the horizontal and vertical meridians.1,28-31 This increased myopic defocus along with reduced peripheral hyperopic blur leads to a decreased stimulus for eye growth, thus halting myopia progression.30

What does the current literature say?
Concerned parents and practitioners alike often have several questions preceding ortho-k treatment. What is the most appropriate age to initiate ortho-k? When should ortho-k be initiated based on the amount and rate of myopia progression? Studies suggest that a young child between the ages of 6-9, who experience an increase in axial length of > 0.20mm/7 months and/or spherical equivalent of myopic progression of greater than or equal to one diopter per year, is an ideal candidate for ortho-k lenses.30,32

Ortho-k has been shown to reduce myopia progression by slowing axial length elongation by slightly less than 50%;14,33,34 ranging from 41-45% in most meta-analyses.1,35,36 When treating patients for myopia control with ortho-k, axial length measurements at baseline and throughout the treatment process are critical. Most studies routinely use axial length elongation as a measure for myopia progression rather than changes in spherical equivalent.30 Axial length elongation was found to be 0.23 + 0.25 mm in ortho-k lens wearers compared to 0.48 + 0.26 mm in single vision spectacle wearers in a two-year prospective pilot study on 35 children (ages 7-12 years).1,37 Throughout the duration of this study, ortho-k lens wearers had a 50% reduction in myopia progression.1,37 Additionally, a one-year study of anisometropic children 7-13 years of age found a statistically significant difference in axial length elongation between the ortho-k eye (0.07 + 0.21 mm, p= 0.038) and fellow eye with no correction (0.36 + 0.23 mm, p<0.001).30,38

In a five-year study of children (ages 8-12 years) fit with ortho-k lenses, myopia progression almost reduced by half during the first year of treatment as compared to children wearing single-vision spectacles.1,33 During the last three years of the study, there was no significant difference in myopia progression rates amongst the two groups. This possibly suggests a tapering effect of myopia control by ortho-k with longer periods of treatment.1,33

With the escalating incidence of myopia, we see advancements in lens designs and instruments. Manufacturers of orthokeratology lens designs are expanding parameters to correct for higher amounts of astigmatism and high myopia.1

While research on the subject matter of myopia control is broad and has answered many questions, further research is needed to comprehend this significant epidemic fully. No one treatment is 100% effective at slowing the rate of myopia progression. One thing is definite, it is imperative to optimize treatment plans for the individual patient, which may now include combination therapies. The overall goal is to ultimately prevent sight-threatening complications in these myopic individuals.



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