Peripheral refraction and ocular shape in children

PURPOSE. To evaluate the relation between ocular shape and refractive error in children. METHODS. Ocular shape was assessed by measuring relative peripheral refract ive error (the difference between the spherical equivalent cycloplegic auto refraction 30 degrees in the nasal visual field and in primary gaze) for th e right eye of 822 children aged 5 to 14 years Participating in the Orinda Longitudinal Study of Myopia in 1995. Axial ocular dimensions were measured by A-scan ultrasonography, crystalline lens radii of curvature by videopha kometry, and corneal power by video-keratography. RESULTS. Myopic children had greater relative hyperopia in the periphery (0.80 +/- 1.29 D), indicating a prolate ocular shape (longer axial Length th an equatorial diameter), compared with relative peripheral myopia and an ob late shape (broader equatorial diameter than axial length) for emmetropes ( -0.41 +/- 0.75 D) and hyperopes (-1.09 +/- 1.02 D). Relative peripheral hyp eropia was associated with myopic ocular component characteristics: deeper anterior and vitreous chambers, flatter crystalline lenses that were smalle r in volume, and steeper corneas, Lens thickness had a more complex associa tion. Relative peripheral hyperopia was associated with thinner lenses betw een refractive error groups but changed in sign to become associated with t hicker lenses when analyzed within each refractive error group. Receiver op erator characteristics analysis of the ocular components indicated that vit reous chamber depth was the most important ocular component for characteriz ing the myopic eye, but that peripheral refraction made a significant indep endent contribution. CONCLUSIONS. The eyes of myopic children were both elongated and distorted into a prolate shape. Thinner crystalline lenses were associated with more hyperopic relative peripheral refractions across refractive error groups, b ut failure of the lens to thin mal account fur the association between thic ker lenses and more hyperopic relative peripheral refractions within a give n refractive group. Increased ciliary-choroidal tension is proposed as a po tential cause of ocular distortion in myopic eyes.