This is a prospective double-blind randomised trial between September 2007 and October 2009. It included 221 children aged 8-13 years, with myopia between -1 and -5 Dioptres ≤1.00D. There were 111 patients in the defocus incorporated soft contact DISC group and 110 in the single vision (SV) contact lens group. The DISC contact lens is a custom-made bifocal soft contact lens of concentric rings design. It comprised a correction zone in the centre and a series of alternating defocusing and correction zones extending towards the periphery having a proportion of 50:50. The correcting zones matched the distant prescription while the defocusing zones were 2.5D relatively negative. Such design allowed to introduce myopic retinal defocus and to maintain clear vision, simultaneously. The single vision lenses were made using the same material with matching parameters without any defocusing zones. The contact lens fitting was performed according to the cycloplegic refraction, corneal curvature and horizontal visible iris diameter. All the patients were measured including the refractive error and axial length at six monthly intervals. The differences between groups were analysed using unpaired t test. One hundred and twenty-eight children completed this study, 65 in the DISC group and 63 in the SV group. It was found that myopia progressed 25% more slowly for children in the DISC group compared to those in the controlled group (0.3 D per year, 95% CI -0.1 to -0.47 v 0.4 D spheres per year; 95% CI -0.93 to -0.65, p=0.031). In addition it was found that the axial length elongation was less in the DISC group compared to the SV group (0.1mm/year comparing 0.18mm/year in the SV group). The effect of the wearing time further increased to 58% when the children had worn the DISC lenses for seven hours per day or more. The marginal benefit from the increased wearing time was smaller when the wearing time reached eight hours. It was found that myopia in children who wore the DISC lenses for five or more hours per day progressed 46% less than those in the SV group. The authors commented that the major limitation was that there was a high dropout rate (approximately 42%); 3/4 dropped out in the first year. The main reason for both groups was lack of motivation in contact wear. The authors conclude that daily wearing of the DISC lenses significantly slowed myopia progression and axial length elongation in Hong Kong schoolchildren. The findings also show that simultaneous clear vision with constant myopic defocus can retard myopia progression.
DISC lens slow myopia progression in Hong Kong Chinese schoolchildren
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