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G. Zeng, S. A. McFadden; Regional Variation in Susceptibility to Myopia From Partial Form Deprivation in the Guinea Pig. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1736.
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Myopia arises from excessive ocular elongation and can be induced by form deprivation (FD) in a growing eye. The control of ocular growth is thought to be contained within the eye, because FD still occurs when the optic nerve is cut1; and if only half the eye is deprived, only that part of the eye elongates and becomes myopic2,3. We sought to discover whether all parts of the mammalian visual field were equally susceptible to partial FD.
Guinea pigs were raised with partial diffusers over one eye from 7-14 days of age to induce local FD. Diffusers covered the superior (S), inferior (I), nasal (N), or temporal (T) visual fields (VF) (n=37). At 14 days of age, refractive error was mapped in different sectors of the VF under cycloplegia. Eyes were cut on a freezing microtome in either the vertical (for S and I) or horizontal (for T and N) plane, and eye shape compared to untreated eyes from digital images of the frozen sections.
Partially deprived eyes became relatively myopic and elongated in the deprived region, but the S-VF was relatively resistant to local change, while the I-VF became excessively myopic and elongated (p<0.001). This asymmetry was not present in the N and T regions. The difference between the two eyes in refractive error and vitreous chamber depth in the deprived region was -7.5, -1.6, -5.6, -5.8D and 137, 90, 20, 45µm for I, S, N and T deprived VF respectively. The resistance of the S-VF to developing local FD myopia was not because of space limitations for growth. Refractive error and ocular shape also changed in the opposite direction in the I and S non-deprived VF (-2.1, +4.8D and +72, -41 µm respectively).
Partial FD of the mammalian eye results in local myopia suggesting that the mechanisms within the retina can be evoked in a spatially restricted manner. However, the sensitivity to FD varies in different retinal regions. We speculate that the resistance of the S-VF to FD and the excessive myopia in the I-VF may be related to the asymmetric distribution of blue and green cones in corresponding retinal regions.1McFadden SA, Wildsoet C. IOVS, 2009, 50: E-Abstract 1620.2McFadden SA. IOVS, 2002 43: E-Abstract 189.3Smith EL et al. IOVS, 2009, 50:5057-5069.
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