The expandability of the eye in childhood myopia

PURPOSE: While intraocular pressure has been shown to have some influence on eye growth, the stress exerted on the outer wall of the eye and the rigidity of the outer coats of the eye may be of greater importance. No studies have assessed the significance of both of these variables in terms of childhood myopia and its progression. METHODS: Twenty myopic and twenty non-myopic children aged 8 to 12 years participated in the study. Refractive error (including refractive error shift over the past year), ocular dimensions (anterior chamber, lens thickness, vitreous chamber, axial length), intraocular pressure, equatorial scleral rigidity, and outer wall thickness were measured for right eyes. Outer wall stress was calculated using the approximation, p = IOP*r/2t. RESULTS: The myopic group was 3.43 D more myopic and had 1.43 mm longer eyes on average than the non-myopic group. The myopic children had experienced a mean refractive shift of -0.30 D/yr over the past year. Equatorial wall thickness was significantly less in myopes than non-myopes (difference of 0.09 mm, p = 0.02) and in the combined sample was correlated to refractive error (r = 0.312, p = 0.05), but not refractive error shift. Ocular rigidity and eye wall stress values were similar in the two groups. The refractive shift increased as wall stress increased both in the combined sample (r = -0.386, n = 35, p = 0.022) and the myopic group (r = -0.600, n = 16, p = 0.014). CONCLUSION: We did not find large differences in wall thickness, ocular rigidity, or wall stress in myopic and non-myopic children. While reduced ocular rigidity, increased wall stress and scleral thinning may have a role in myopia progression in childhood we were not able to clearly show this in our study of 40 children