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Kristen Totonelly, Xiaoying Zhu, Pearl Thai, Rinita Zanzerkia, Debora L Nickla; The association between initial choroid thickness and subsequent ocular growth rate in young chicks: Evidence for different choroidal mechanisms in growth inhibition vs stimulation. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3595.
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Thick choroids are associated with ocular growth inhibition and thin choroids with growth stimulation. Whether this is relevant to the mechanisms underlying the signal cascade that mediates scleral growth in response to visual or pharmacological stimuli is unknown. These studies asked whether choroid thickness in young chicks predicts subsequent ocular growth rates under various conditions.
We determined the correlation between choroid thickness and subsequent ocular growth rate (scleral GAG synthesis for group 6) under the following conditions. (1) Plus lens-wear for 4 days (d) (n=14). (2) Minus lens-wear for 5 d (n=16). (3) Diffuser-wear for 5 d (n=16). (4) Fellow untreated eyes (n=53). (5) Daily injections of quinpirole (n=12), apomorphine (n=17), atropine (n=11), pirenzepine (n=10), or a single injection of oxotremorine (n=27). (6) Eyecups of RPE, choroid and sclera cultured for 24 hrs (n=9). Some of these data are retrospective.
There was a negative correlation between initial choroid thickness and subsequent ocular growth rate in visual conditions in which eye growth was inhibited (plus lens: r=-0.662, p<0.01) and in untreated eyes (r=-0.393, p<0.005), but not when growth was stimulated (minus lens: r=0.08, p=0.72; diffusers: r=0.036, p=0.9). In untreated eyes and in eyes wearing diffusers or minus lenses there was also a correlation between initial choroid thickness and subsequent thinning (p<0.05); there was no such correlation for plus lenses. In eyecups, there was a negative correlation between choroid thickness and scleral GAG synthesis (r=-0.79, p<0.01). Drugs: There was a negative correlation between choroid thickness and growth rate in eyes injected with quinpirole (r=-0.72, p=0.008) but the data for apomorphine did not reach significance. There was no correlation for eyes injected with muscarinic agents.
That initial choroidal thickness does not predict ocular growth rate under all conditions implies that thickness is not correlated with the efficacy of a mechanical barrier to a signal molecule. This is also supported by the negative correlation between thickness and quinpirole-mediated growth inhibition. Finally, the results support different roles for the choroid in growth stimulation vs inhibition.
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