The Influence of Baseline Relative Peripheral Refraction in Myopia Control Using Myopic Defocus

Myopia has become a world concern and its prevalence has increased in recent decades. Myopic defocus has been applied for slowing down the axial elongation and myopia progression, which is mainly based on the theory of simultaneous competing defocus and peripheral optics. Defocus Incorporated Multiple Segments (DIMS) spectacle lenses impose myopic defocus in the central or peripheral retina, with myopia progression being retarded by 50% to 60%. However, the optimal amount of myopic defocus has not yet been determined. Relative peripheral refraction (RPR) is used to indicate the difference between peripheral refraction and central refraction. Previous studies showed that retinal shape determined RPR, and baseline RPR may influence the myopia control efficacy using DIMS lenses on myopic children. It is still unclear if any other unknown factor influenced the final myopia control outcome in these young children with myopic RPR at baseline. Unlike our previous study8 that bias on hyperopic RPR children (myopic RPR, n = 27; hyperopic RPR, n = 52), this study is a case-control study with the same sample size for each RPR group. We will also include younger children who are more prone to have myopic RPR and develop high myopia. The results should provide new insight into the myopia control strategy in early-onset myopic children.

In the current study, we will investigate the influence of baseline RPR in myopia retardation using DIMS lenses among young myopic children.

This will ba a 1-year prospective clinical trial. Through G*Power (version 3.1.9.6) calculation, 80 healthy myopic subjects (40 myopic RPR vs 40 hyperopic RPR) aged 5-9 years should be needed. After screened by inclusion criteria, eligible participants will be assigned to wear DIMS lenses for 1 year (12 months, 8 hour per day, 7 days per week). This study includes 5 visits: Visit 1: baseline, Visit 2: lens dispensing, Visit 3: 2-week follow-up, Visit 4: 6-month follow-up, and Visit 5: 12-month follow-up. All eye examinations will be carried out in the Optometry Research Centre (A137), the School of Optometry, the Hong Kong Polytechnic University. The main data collection, including refractive error, axial length, related ocular parameters will be measured at baseline, 6-month and 1-year visits. At the lens dispensing and 2-week follow-up visits, vision acuity testing and computer scanning of posterior eyes will be measured. New DIMS lens will be replaced and upgraded if the equivalent sphere of refraction (SER) is changed or visual acuity change.

The following data will be statistically analyzed. The primary outcome data include the difference in change in SER with cycloplegia between the myopic and hyperopic RPR from the baseline over 12 months of treatment. Secondary outcomes data include the changes in axial length, peripheral refraction, relative peripheral refraction, the amplitude of accommodation, lag of accommodation, corneal curvature, phoria and stereoacuity.