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Christopher M. Dillingham, Jeremy A. Guggenheim, Jonathan T. Erichsen; Centrifugal Visual System Influences Early Refractive Development. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3432.
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© ARVO (1962-2015); The Authors (2016-present)
We investigated the role of the centrifugal visual system (CVS), which projects from the brain to the retina, in emmetropization.
To disrupt CVS efferents to the retina, lesions of the isthmo-optic nucleus/tract or sham surgeries were performed on 4-5d posthatch chicks (n=57; Shaver-Blacks) raised under 14hrL/10hrD conditions. Before surgery, refractive state and corneal radius of curvature were measured using retinoscopy and IR video-keratometry, respectively. At 7 and 21d post-surgery, in addition to retinoscopy and keratometry, A-scan ultrasonography determined the axial dimensions of the anterior chamber, crystalline lens, and vitreous chamber depth (VCD) as well as their sum, axial length. Intra-vitreal injection of WGA was made contralateral to the lesion, followed 48hr later by perfusion fixation, sectioning, anti-WGA immunohistochemistry and stereological analysis. Counts of remaining (i.e. labeled) centrifugal neurons were compared to sham controls to determine lesion success.
At 7d post-surgery, chicks with >90% CVS disruption (n=12) developed significant hyperopia (1.99D±2.99D) in the treated (contralateral) eye relative to the control (ipsilateral) eye, when compared to subjects with 50-90% lesion success (1.57D±0.56D, n=30, p<0.05), but this anisometropia did not reach significance when compared with 0-10% (2.15D±0.82, n=6, p=0.07) or 10-50% (2.10D±0.82, n=6, p=0.082) lesion success groups. The anisometropia and difference in VCD were correlated (r=0.76, p<0.001), suggesting that this hyperopia was axial in nature. At 21d post-surgery, the induced hyperopia was no longer present. During the period between 7 and 21 days post-surgery, the mean difference in the refractive change was significantly greater in the initially hyperopic >90% lesion group (-2.86D±2.58D) when compared to the 50-90% (-0.27D±1.37D, p<0.001), 10-50% (0.38D±0.76D, p<0.01) and 0-10% lesion success groups (0.12D±0.98D, p<0.01). Also, although not significant, a trend towards an over-correction of the initial induced hyperopia was observed, with anisometropia showing a negative correlation with ungrouped percentage lesion success (r=-0.24, p=0.079) at 21d post-surgery.
Unilateral disruption of centrifugal efferents to the retina of the contralateral eye appears to result in an initial axial hyperopia that is subsequently reversed in a developmentally-induced recovery period characterized by up-regulated vitreous chamber growth of the previously hyperopic eye.
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