Methodological quality of the review: Low confidence
Author: Yue M. Liu and Peiying Xie
Subsector: Safety of orthokeratology
Equity focus: No
Study population: Community and clinical based
Type of programme: Hospital based
Review type: Other review
Quantitative synthesis method: Systematic review
Qualitative synthesis method: Not applicable
Background: Orthokeratology (also known as OrthoK, OK, corneal reshaping, corneal refractive therapy and vision shaping treatment) is an alternative method to correct refractive errors using custom-designed rigid lenses to temporarily modify the curvature of cornea. Currently, the most common clinical application of OrthoK is for the reduction of myopia through corneal flattening. OrthoK, among other novel contact lens designs being investigated, has been shown in multiple clinical studies as effective in slowing down myopic progression. Combining its unique advantage of providing clear unaided vision during daytime, overnight OrthoK has become one of the most popular choices among children for refractive correction. However, with the rapid increase of the utilisation of OrthoK worldwide, potential complications associated with this treatment, especially used as overnight modality, have become a significant concern.
Objectives: The objective of this review was to evaluate the ocular safety of orthokeratology (OrthoK) treatment of myopia correction and retardation.
Main findings: This review incorporated a total of 170 publications, including 58 English and 112 pieces of Chinese literature. The risk of microbial keratitis in overnight OrthoK was similar to that of other overnight modality. The most common complication was corneal staining. Other clinically insignificant side effects included epithelial iron deposit, prominent fibrillary lines and transient changes of corneal biomechanical properties. There was no long-term effect of OrthoK on corneal endothelium.
Methodology: Data from all types of relevant clinical studies, including case series, case reports, patient/practitioner surveys, retrospective and prospective cohort studies and clinical trials was included in the review. Because the focus of the review was on the incidence of side effects related to OrthoK, there was no limitation on the primary objective of the studies; that is, whether the treatment was used for myopia correction or for myopia control. Similarly, publications on OrthoK lenses used as overnight or daytime wear modalities were both included in the review. As a large proportion of previously published OrthoK-related complications were from East Asia, especially from China, the literature published both in English and Chinese was identified from the Cochrane Library, Medline, Embase, CNKI, CQVIP and Wangfang Data.
Applicability/external validity: The authors acknowledge some limitations to consider during interpretation or for external use of the findings: despite the large number of studies identified and included in the review, the absolute incidences of OrthoK-associated side effects were difficult to evaluate because of significant potential sampling bias, publication bias, and lost to follow-ups. Additionally, the wide variety of study designs made it difficult to perform meta-analysis, so only the results from individual relevant studies were reported. Finally, owing to the time constraints, no further effort was made to contact the investigators of each study to clarify unclear data presentations in the original publications, or to acquire necessary raw data to improve the efficiency of the data usage in the analysis.
Geographic focus: Not discussed.
Summary of quality assessment:
Low confidence was attributed in the conclusions about the effects of this study, as important limitations were identified. Literature searches were not comprehensive enough to ensure that all relevant studies were identified and included in the review. Methods used to extract data were not rigorous to ensure that biases were avoided, and methodological assessment of included studies was not conducted.