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V. Choh, V. Padmanabhan, K. Kuo, J. Ni, C.F. Wildsoet; Colchicine Attenuates the Minus Lens but Not Plus Lens Compensation in Chick . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1989.
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Purpose: Studies showing that optic nerve–sectioned (ONS) chick eyes are capable of responding to both negative and positive lenses suggest that emmetropisation is locally regulated. However, there are subtle changes to eye growth in ONS eyes that may be related to the loss of retinal ganglion cells after ONS. Colchicine, a cytotoxin that destroys retinal ganglion cells, was used to further examine the effects of retinal ganglion cell loss on emmetropisation. Methods: White leghorn chicks (Gallus gallus domesticus) were injected in one eye with colchicine and in the other eye with saline on the day of hatching (P0). Colchicine–injected eyes were treated with a –10 D lens, a +10 D lens, or were left ungoggled (n=5 per group). Saline–injected eyes were ungoggled. Refractive errors and axial lengths of the various ocular components of both eyes were measured prior to lens–wear, and again 3, 5 and 8 days later. Results: Colchicine–injected eyes were initially more hyperopic (mean, SD: +7.14 ± 3.58 D) than their fellow eyes (+4.18 ± 0.73 D), and exhibited shallower anterior chamber depths (relative difference: –0.19 ±0.12 mm) and thinner lenses (–0.08 ±0.04 mm). The refractive error (RE) of the no lens group did not change significantly over the lens–wearing period (p=0.1400; mean interocular change: –1.55 ± 2.97 D), while the +10 D and –10 D lens groups showed hyperopic (p<0.0001; +8.78 ±2.79 D) and myopic changes (p=0.0531; –2.75 ± 3.76 D,), respectively. Only the +10 D lens changes were significantly different than those for the ungoggled birds (p<0.05). Differences in RE were mainly related to changes in the vitreous chamber depths, which for the +10 D–treated eyes, were shorter than their fellow eyes (mean difference after 8 days: –0.32 ±0.31 mm), and for the –10 D–treated eyes, were longer than their fellow eyes (0.22 ±0.12 mm). However, neither of these 2 lens group changes was significantly different from that for the no lens group (0.04 ± 0.17 mm). Conclusions: Although both colchicine and ONS destroy retinal ganglion cells, they have different effects on eye growth and emmetropisation. Colchicine but not ONS reduces anterior chamber growth while ONS reduces vitreous chamber growth. Also, although colchicine–injected eyes, like ONS eyes, show compensatory responses to imposed defocus, compensation is attenuated for –10 D lenses in the former and for +10 D lenses in the latter.
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