Orthokeratology (ortho-k) or corneal reshaping has been utilized clinically over the past decades for both vision correction and for myopia progression management. This article will present some of the most pertinent and current research as it relates to ortho-k and myopia management.
Efficacy of Ortho-k for Myopia Management
The evidence that ortho-k can have a positive effect on slowing the progression of myopia is well agreed upon. A recent study from Denmark investigated the efficacy of overnight ortho-k contact lenses versus single-vision spectacles (Jakobsen and Møller, 2021). Investigators assigned 60 children ages 6 to 12 years to either overnight ortho-k or single-vision spectacles. Entering spherical refractive error was –0.50D to –4.75D, with 2.50D or less of refractive astigmatism. After 18 months, the average axial elongation in the ortho-k group was 0.24mm (59%) less than in the spectacle lens-wearing group. Furthermore, there were no fast progressors (> 0.75D/year) in the ortho-k group as compared to 22% of subjects in the spectacle lens-wearing group.
VanderVeen et al (2019) reviewed published evidence to evaluate ortho-k’s ability to reduce myopia progression in children and adolescents in comparison with spectacles or daytime contact lens use for standard refractive correction. Searches of the PubMed database, the Cochrane Library, and the databases of clinical trials yielded 162 citations, of which 13 were selected for assessment. These studies indicate that ortho-k typically reduced axial elongation by approximately 50% over a two-year study period. Average axial length (AL) change values were approximately 0.3mm for ortho-k patients compared with 0.6mm for control patients, which corresponds to an approximate difference in refraction of 0.50D. Ortho-k may have a greater effect on younger age groups and in individuals who have larger-than-average pupils. The authors concluded that ortho-k may slow myopia progression, with a potentially greater effect when initiated at an early age (6 to 8 years).
Influence on Axial Length
Ortho-k’s potential to reduce the degree of AL increase in myopic individuals is of great value. Na and Yoo (2018) conducted a retrospective study that specifically evaluated the influence of ortho-k on AL increase. They reviewed medical records of 45 monocular myopic subjects 7 to 13 years of age who were treated with monocular ortho-k lens wear. The monocular myopia ranged from –0.75D to –4.25D, with near emmetropia in the contralateral eye and with-the-rule astigmatism of –1.50D or less.
After 12 months of lens wear, AL had increased by 0.36mm ± 0.23mm in the control eyes (P < 0.001) but by only 0.07mm ± 0.21mm) in the ortho-k eyes (P = 0.038). Nine subjects who were followed for two years showed no AL change (0.16mm ± 0.25mm) in the ortho-k eyes (P = 0.095) compared to significant AL growth (0.38mm ± 0.26mm; P = 0.002) in the control eyes. The control eyes showed progressive AL growth throughout the study for the near emmetropic eye compared with the monocular ortho-k lens eye.
Ortho-k Design Differences
Ortho-k lens design differences have been proposed to influence the ability to control AL and myopia progression. Nakamura et al (2021) conducted a multicenter study in Japan that evaluated 105 school-aged children wearing single-vision spectacles and 89 school-aged children wearing one of three ortho-k lens types. The researchers found no relationship between refractive error change and ortho-k lens type. They concluded that myopia progression was suppressed in school-aged children regardless of design.
Guo et al (2021) reported the one-year results of a study that investigated the myopia control effect of ortho-k lenses with different back-optic-zone diameters (BOZDs). Children aged 6 to < 11 years who had myopia ranging from –0.75D to –4.00D were randomly assigned to wear ortho-k lenses with either a 6mm or a 5mm BOZD. The 5mm group demonstrated slower axial elongation (0.04mm ± 0.15mm) compared to the 6mm group (0.17mm ± 0.13mm) (p = 0.001). There was a significant positive correlation between the horizontal treatment zone size and axial elongation (r = 0.36, p = 0.006).
The researchers concluded that a smaller BOZD resulted in a reduced treatment zone, with slowing of axial elongation by 0.13mm compared to with conventional 6mm BOZD ortho-k lenses.
Combination therapies are explored if monotherapy treatments are not successful in decreasing the progression of AL or myopic refractive error. Conceptually, ortho-k can work in combination with topical atropine therapy, because it is likely that they have different mechanisms of action.
Zhou et al (2021) conducted a small study of 42 subjects that evaluated the adjunctive effects of ortho-k and atropine eye drops in Chinese children. Subjects aged 8 to 13 years who had a spherical equivalent refractive error of –2.00D to –5.00D were categorized into two groups: combination group (ortho-k and 0.01% atropine) or atropine group (0.01% atropine). After two years, the average spherical equivalent refraction change was 0.88D ± 0.31D in the combination group and 1.14D ± 0.63D in the atropine group (P = 0.026), with an average progression in AL of 0.50mm ± 0.17mm and 0.61mm ± 0.21mm, respectively (P = 0.091). The authors concluded that the combination therapy of ortho-k and 0.01% atropine eye drops was more effective in reducing progression of myopia compared to atropine monotherapy, with greater effect in children who had a younger baseline age (8 to 10 years) or shorter baseline AL (22.00mm to 24.50mm).
However, recent findings that have suggested questionable therapeutic effect of atropine 0.01% (Yam et al, 2019) make us question whether combination therapy is more effective when we compare it to only atropine 0.01% therapy. Future outcomes from studies that evaluate ortho-k in combination with higher concentrations of atropine are needed.
Ocular Health and Safety
Although the benefits of controlling myopia progression are now quite well known, we must always determine risks versus benefits. Davis et al (2015) found no differences in complication rates between patients wearing ortho-k lenses and controls who wore daytime-wear monthly replacement soft contact lenses. After three years, there was no statistically significant loss of best-corrected visual acuity in either the test or the control group. This is a critically important safety measure of both vision correction modalities, especially when considering that we are implementing treatment for children.
Liu and Xie published a systematic review of the safety of ortho-k in 2016. This review incorporated 170 publications, of which 58 were in English and 112 were from Chinese literature. They found that the risk of microbial keratitis in overnight ortho-k was similar to that with other overnight modalities. Corneal staining was the most common complication. Other side effects reported that were clinically insignificant included epithelial iron deposit, prominent fibrillary lines, and transient changes of corneal biomechanical properties. Ortho-k had no long-term effect on the corneal endothelium. The authors concluded that sufficient evidence exists to suggest that ortho-k is a safe option for myopia control. A well-fit lens, rigorous compliance to lens care regimen, patient adherence to routine follow up, and prompt treatment of complications are required for ortho-k to succeed in the long term.
Hu et al (2021) looked specifically at the safety of ortho-k in children. They retrospectively reviewed medical records of patients who started ortho-k for myopia correction and continued for more than one year. This included a total of 489 eyes from 260 patients who had ages ranging from 8 to 15 years and spherical equivalent refraction of –1.00D to –6.00D. Corneal adverse events (AEs) occurred in 111 eyes (22.7%) during the one-year follow-up period, including corneal staining (n = 106) and corneal infiltrates (n = 5), with a 6.9% incidence of significant AEs. The authors concluded that ortho-k is a safe option for myopic children. Risk factors for corneal AEs in ortho-k wearers included younger age, higher myopia, and allergic conjunctivitis. The only risk factor for significant AEs was high myopia.
Myopia progression and higher degrees of myopia impact both ocular health and quality of life. Currently, a number of evidence-based therapeutic approaches have been shown to slow down AL elongation and progressive myopic refractive error. One of the most effective and widely used treatments is corneal reshaping or ortho-k. CLS
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