Orthokeratology with increased compression factor (OKIC): study design and preliminary results

Kin Wan, Jason Ki-Kit Lau, Sin Wan Cheung, Pauline Cho, Kin Wan, Jason Ki-Kit Lau, Sin Wan Cheung, Pauline Cho

Abstract

Objective: To present the study design and the baseline data of a prospective cohort study investigating the safety, refractive correction and effectiveness of myopia control in subjects fitted with orthokeratology (ortho-k) lenses of different compression factors.

Methods and analysis: This study is a 2-year longitudinal, double-masked, partially randomised study. Myopic children aged between 6 and 10 years are recruited and they may choose to participate in either the ortho-k or spectacle-wearing group. Subjects in the ortho-k group are randomly assigned to wear ortho-k lenses of either conventional compression factor (CCF, 0.75 D) or increased compression factor (ICF, 1.75 D). For the ortho-k subjects, the time and between-group effects within the first month of lens wear were analysed.

Results: Sixty-nine ortho-k subjects (CCF: 34; ICF: 35) and 30 control subjects were recruited. There were no significant differences in baseline demographic data among the three groups of subjects (p>0.19). At the 1-month visit, the first fit success rates were 97% and 100% in the CCF and ICF ortho-k group, respectively. A higher percentage of ICF subjects could achieve full correction (CCF: 88.2%; ICF: 94.3%). The change in axial length was significantly higher in the ICF group (CCF, 0.003 mm; ICF, -0.031 mm) (p<0.05). No significant between-group differences in daytime vision or in the coverage and depth of corneal staining between the two ortho-k groups (p>0.05) were observed at any visit.

Conclusion: ICF did not compromise the corneal integrity and the lens centration within the first month of lens wear. The preliminary performance of ortho-k lenses with ICF of 1.00D shows that it was safe to be used in the longer term for the investigation of myopia control.

Trial registration number: NCT02643342.

Keywords: contact lens; optics and refraction; treatment other.

Conflict of interest statement

Competing interests: None declared.

© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

Figures

Figure 1
Figure 1
Flowchart of the conduct of the study. *CF, compression factor.
Figure 2
Figure 2
Changes in myopia in ortho-k subjects wearing lenses of conventional compression factor (CCF) and increased compression factor (ICF). Error bars indicate the SD. The asterisk (*) denotes a significant difference in myopia between groups. BL, baseline; ON1, first overnight; Wk1, first week; Wk2, second week; M1, 1 month.
Figure 3
Figure 3
Severity (coverage) of central corneal staining in conventional compression factor (CCF) and increased compression factor (ICF) groups. BL, baseline; ON1, first overnight; WK1, first week; WK2, second week; M1, 1 month; G0–G1: grade 0 to grade 1.

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