April 3, 2023
By Ornella Koumbo, PhD, Brien Holden Vision Institute
Anisometropia, an inconsistency in the refractive status between the two eyes of an individual, is gaining interest as there is some indication that there is a higher rate of myopia progression in anisometropic children. The mechanisms underlying the development of asymmetric axial elongation are not fully understood. Orthokeratology is found to be an effective treatment modality to slow myopia progression, but so far, its role in anisometropic children has not been systematically studied.
Tsai et al. conducted a meta-analysis of the evidence to elucidate the efficacy of OrthoK for anisometropia control. A total of nine retrospective cohort studies and one prospective study were included in the review. Unilateral myopia was assessed in five retrospective studies, and bilateral anisometropia was investigated in eight studies, including one prospective and seven retrospective studies. The primary outcome was the inter-eye axial length elongation difference between the high myopic and low myopic eyes in the bilateral anisomyopia group or the myopic eye and emmetropic eye in the unilateral myopia group.
The results indicate that OrthoK appears to reduce the inter-eye axial length difference. In the unilateral anisomyopes, the mean difference at the end of a two-year follow-up had reduced to -0.17 mm, whereas it was -0.27 mm at the end of the one-year follow-up. However, in the bilateral anisomyopes, the pattern was inconsistent, with a lesser mean difference observed at the one-year follow-up than at the two-year follow-up. It is possible that the more significant effect observed in unilateral anisomyopes could be due to the lack of need for treatment in the fellow eye, i.e., the axial length growth rate of the fellow eyes would have followed their natural course, which was inherently faster than that of myopic eyes with OrthoK lenses.
The evidence from this study suggests that OrthoK lenses significantly decreased the inter-eye axial length difference in bilateral anisomyopic and especially unilateral myopic children during one-year and two-year treatment periods. In addition, reviewing all the included studies, few serious side effects were noted. Thus, OrthoK may be a safe clinical method to retard myopic progression coupled with reducing anisomyopic value. However, additional well-structured randomized control trials or prospective studies with longer follow-up duration are warranted.
Effect of Orthokeratology on Anisometropia Control: A Meta-Analysis
Hou-Ren Tsai, Jen-Hung Wang, Cheng-Jen Chiu
Background: The effectiveness of orthokeratology in retarding anisometropic progression has been investigated in several small-sample studies. This quantitative analysis aimed to elucidate the efficacy of orthokeratology for anisometropia control.
Methods: We searched PubMed, Embase, and Cochrane databases for relevant studies through September 2020. Axial length (AL) data at baseline and final follow-up were extracted, and AL elongation and difference were calculated. Methodological quality was evaluated using the risk of bias in non-randomized studies of interventions (ROBINS-I) tool. Meta-analyses were performed using a fixed-effect model based on heterogeneity.
Results: A total of 10 cohort studies (nine retrospective studies; one prospective study) were included. The pooled results for the unilateral myopia group showed that the mean AL elongation difference between myopic and emmetropic eyes was -0.27 mm (95% CI, -0.31 to -0.22; p < 0.01) at the one-year follow-up (four studies) and -0.17 mm (95% CI, -0.33 to -0.02; p = 0.03) at the two-year follow-up (two studies). In the bilateral anisomyopic group, mean AL elongation difference between high and low myopic eyes was -0.06 mm (95% CI, -0.09 to -0.04; p < 0.01) at the one-year follow-up (seven studies) and -0.13 mm (95% CI, -0.21 to -0.06; p < 0.01) at the two-year follow up (three studies).
Conclusion: This study demonstrated that orthokeratology can effectively retard myopic progression and reduce anisomyopic values. However, additional well-structured randomized controlled trials or prospective studies with longer follow-up periods are warranted to address this topic in more detail.
Tsai, H. R., Wang, J. H., & Chiu, C. J. (2021). Effect of orthokeratology on anisometropia control: A meta-analysis. Journal of the Formosan Medical Association, 120(12), 2120-2127.
|Dr. Ornella Koumbo is a qualified optometrist, currently employed by the Brien Holden Foundation, working within the Haiti Optometry School Project as the Senior Lecturer and Course Coordinator at the Universite d’Etat d’Haiti in Port au Prince, Haiti. Dr. Koumbo is a dedicated educator who is committed to providing the new cohorts of students with the knowledge and skills they need to succeed in the field of optometry and service their local communities. She earned her degree in optometry from the Bausch + Lomb School of Optometry, and she earned her PhD in optometry from the University of New South Wales, supported by BHVI. Dr. Koumbo’s research focuses on myopia control, refractive error correction, and optical equipment. She has a continuing interest in research and has ambitions to continue following similar research topics with greater depth in the future.|