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Guang Zeng, Sally McFadden; Inhibition in peripheral scleral lengthening during the development of myopia in the guinea pig. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5180.
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Human myopic eyes elongate posteriorly and show relative peripheral hyperopia. Since hyperopic defocus induces myopia in animal models, these peripheral changes in myopic eyes are thought to cause the progression of central myopia. Since the sclera is remodelled and thins in myopic eyes and its structural integrity determines the shape of the eyeball, we studied the changes in the length of the sclera during the development of form deprivation myopia, to determine the relationship between central and peripheral changes in ocular growth.
31 guinea pigs were monocularly form deprived (FD) from 6 days of age for periods of 8, 14, 23 or 63 days in 4 different groups. At the end of the FD period, eyes were enucleated, quickly frozen, and cut on a freezing microtome in the horizontal plane 1. Eye shape was analyzed from digital images of the frozen sections and the perimeter lengths of the sclera were calculated for every degree. 1. Zeng G, McFadden SA. The development of eye shape and the origin of lower field myopia in the guinea pig eye. Vision Res. 2012,76:77-88.
Myopic ocular elongation was specifically centered on either side of the optic nerve exit (the peripapillary zone or PPZ) with rapid expansion in the length of the sclera after 8 days of FD in the PPZ (increase of +5.3 μm/deg) accompanied by smaller increases in the length of the sclera in the periphery, particularly in nasal retina (+1.5 μm/deg). Absolute peripheral inhibition in scleral length started in the second week of FD, after the initial elongation in the PPZ, and was present throughout the periphery. After 3 weeks of FD, shrinkage was present in 6/8 animals (mean, -1.3 μm/deg). However, the relative difference between center and periphery increased over time. By 9 weeks of FD, the sclera length had increased further in the PPZ (to +9.0 μm/deg ) so that the difference between the PPZ and the periphery was now maximised.
During the development of myopia, the sclera in the peri-papillary zone surrounding the optic nerve rapidly expanded, and this expansion occurred prior to inhibition in the length of the sclera in the periphery, suggesting that a weakened sclera in the PPZ may induce the peripheral changes. Conversely, the subsequent inhibition in peripheral sclera growth was followed by lengthening in the sclera in the PPZ and this may be the source of the subsequent progression of myopia.
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