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Diane Nava, Alice Chang, Lisa Ostrin, Zhi Chen, Christine Wildsoet; Neurochemical Ablation of Peripheral Glucagonergic Amacrine Cells in the Chick Retina and its Effects on Axial Eye Growth and Refractive Error. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4037.
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© ARVO (1962-2015); The Authors (2016-present)
Several recent myopia studies have pointed to important influences of the peripheral retina on emmetropization. The purpose of this study was to investigate whether mini-bullwhip glucagonergic amacrine cells (MBW), which reside mostly in the dorsal peripheral retina of chicks, contribute to eye growth regulation.
To ablate MBW cells, an intravitreal injection of 250 ng of colchicine was given at p7 (Fischer et al 2008); control birds received saline injections. The retinal effects of the latter treatment were assessed using in vivo SD-OCT imaging and immunohistochemistry (anti-glucagon labeling) on retinal wholemounts and vertical sections. Retinal function was assessed with flash and pattern electroretinography (ERG). Monocular defocusing lenses (+5D single vision (SV), or multifocal (MF) with a +5 D peripheral power and 4.5, 5.5 or 6.5 mm central zone diameters (CZD), were fitted 5 days after injections, and worn for 5 days. Refractive errors and ocular axial dimensions were tracked using retinoscopy and high-resolution A-scan ultrasonography respectively. Finally, equatorial diameters were obtained from photographs of enucleated eyes.
Colchicine induced significant retinal thinning in both peripheral and central retina (p<0.01; p<0.05), and significantly reduces the number of MBW in the peripheral retina (p=0.004) without affecting glucagonergic cells in central retina (p=0.449). It also decreased the amplitudes of b and c-waves as well as the Oscillatory Potential 1 in flash ERG recordings; in pattern ERG recordings, the p50 amplitude was reduced and delayed. All lens treatments inhibited axial ocular elongation and induced hyperopia. There was no difference between the responses to SV and MF lenses in colchicine-treated eyes, contrasting with the previous finding that MF lenses inhibited axial elongation more than SV lenses in normal eyes (Liu and Wildsoet 2011). There was no difference in equatorial diameters between control and colchicine groups.
MBW cells appear to be part of the pathway involved in spatial pattern processing by the retina and also appear to contribute to the response to peripheral myopic defocus. The changes in the c-wave component of the ERG suggest changes in RPE function, which may also contribute to the observed changes in responses to MF lenses.
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