Myopia control with orthokeratology contact lenses in Spain (MCOS): study design and general baseline characteristics

Purpose: Although previous studies suggest that orthokeratology contact lens wear slows eye growth in children with progressing myopia, some limitations in the methodology employed have become evident. Furthermore, the safety of this modality of visual correction has not been assessed. The study "Myopia Control with Orthokeratology Contact Lenses in Spain" (MCOS) is being conducted to compare axial length growth between white European myopic children wearing orthokeratology contact lenses (OK) and wearing distance single-vision spectacles (SV). Additionally, the incidence of adverse events and discontinuations is also recorded. We outline the methodology and baseline data adopted. Methods: Subjects aged 6 to 12, with myopia ranging from 0.75 to 4.00 D and astigmatism ≤1.00 D were prospectively allocated OK or SV correction. Measurements of axial length, anterior chamber depth, corneal topography, cycloplegic autorefraction, visual acuity and corneal staining are performed at 6-month intervals. The incidence of adverse events and discontinuations are also recorded. Results: Thirty one children were fitted with OK and 31 with SV correction. Eight subjects did not meet the refraction-related inclusion criteria for enrollment. No significant differences were found in baseline mean age and refractive and biometric data between the two groups (P>0.05). No adverse events were found in any of the two groups at baseline. Conclusion: To the authors' knowledge, MCOS is the first prospective clinical trial to assess the safety and efficacy of orthokeratology contact lens wear to slow myopia progression vs. single-vision spectacle wear. The MCOS offers a number of notable features: prospective design; well-matched samples and high-resolution ocular biometry measures, which should collectively elucidate whether orthokeratology contact lens wear is a feasible and safe method for myopia-progression control.