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B. Dhillon, J. Armani, D. L. Nickla; The Ocular Growth Inhibition Effected by Dopamine Agonists and Atropine Is Associated With Transient Increases in Choroidal Thickness in Chicks. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1732. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Both the dopaminergic and cholinergic systems have been implicated in ocular growth regulation: dopamine agonists and cholinergic antagonists prevent development of myopia in response to negative lenses. In addition, the ameliorating effects of brief periods of vision may act via dopamine release (McCarthy et al.; 2007). Because there is mounting evidence that the choroidal response to defocus plays a role in ocular growth regulation, we asked whether both systems elicit transient thickening of the choroid concomitant with the growth inhibition.
Negative lenses mounted on velcro rings were worn on one eye starting at age 8-14 days. Intravitreal injections (20-30 ul) of drug (dissolved in saline) or saline, were given through the superior temporal sclera using a 30G needle. Dopamine agonists & atropine: eyes were injected daily for 4 days and the lenses immediately replaced. Apomorphine (non-specific; n=17), quinpirole (D2; n=10), atropine (cholinergic antagonist; n=10), saline controls (n=12). Dopamine antagonist (methylergonovine; n=6): eyes were injected daily for 4 days immediately prior to removing the lenses and allowing 2 hours unrestricted vision; saline controls (n=7). Axial dimensions were measured using high frequency A-scan ultrasonography at the start of lens wear, and on day 4 prior to the injections, and then again 3-4 hours later. Refractive errors (RE) were measured using a Hartingers refractometer.
Apomorphine, quinpirole and atropine inhibited the response to the hyperopic defocus induced by the negative lenses (RE respectively vs saline controls: -1.3 D, 1.2 D and -2.1 D vs -5.6 D; p<0.05 for all). This effect was axial; all drugs prevented the excessive elongation (change in axial length respectively: 233, 205, and 223 um vs 417 um; p<0.01 for all). All three drugs were also associated with a transient thickening of the choroid over 3 hours (41, 32, and 42 um vs -9 um; p<0.05 for all) that did not summate: choroids thinned significantly over the 4 day period in all lens-wearing eyes (respectively: -154 um, -168 um, -71 um and -137 um). Preliminary data suggest that methylergonovine at least partly prevented the ameliorating effects of the periods of vision; lens-wearing eyes grew significantly faster than their fellow control eyes (180 vs 22 um; p<0.05).
The growth inhibition caused by dopamine agonists and atropine is concomitant with brief transient increases in choroidal thickness, further supporting a role for the choroidal responses in the signal cascade mediating ocular growth regulation.
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