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Title: Cyclic AMP inhibits lens-induced myopia development in chicks
Authors: Wong, CL
Chun, RKM
Chung, RHL
Li, KK
To, CH 
Do , CW 
Issue Date: 2010
Source: IMC 2010 13th International Myopia Conference 2010, July 26-29, 2010, Tubingen, Germany How to cite?
Abstract: Purpose: Cyclic adenosine monophosphate (cAMP) is a second messenger known to be involved in regulating many biological processes. The aim of this study was to determine the effect of intravitreal cAMP injection on myopia development in young chicks.
Methods: White Leghorn chicks (Gallus gallus) were used. Three different intensities of optical defocus (i.e. -10D, plano and +10D) were applied bilaterally in chick eyes. Eight-day after hatching, refractive errors were induced by securing a pair of (a) -10D; (b) plano; and (c) +10D lenses in both eyes. At the same time, one eye was injected intravitreally with cAMP once a day for 4 consecutive days while the fellow eye was injected with saline as control. Refractive errors and ocular axial dimensions were determined by retinoscopy and A-Scan ultrasonography, respectively.
Results: Intravitreal injection of 0.1mM 8-Br-cAMP (N=10; P<0.01) and 1mM 8-BrcAMP (N=6; P<0.01) totally inhibited the myopia induced by hyperopic defocus. The administration of another cAMP analog (1mM dibutyl-cAMP) also slowed the lens-induced myopia development in chicks (N=6; P<0.01). These results were accompanied by a parallel significant increase in choroidal thickness, decrease in vitreous chamber depth and axial length, as compared to the control fellow eye. In contrast, cAMP had no effect on refractive errors (N=6; P>0.05) and ocular axial dimensions (N=6; P>0.05) in chicks mounted with bilateral +10D lens (myopic defocus). In chicks mounted with plano lens, cAMP increased the hyperopia (N=8; P<0.05) but had no significant effect on ocular dimensions (N=8; P>0.05) when compared with the fellow eye.
Discussion and Conclusions: Our data suggest that intravitreal administration of cAMP inhibits the myopia development and slows the axial elongation elicited by optical defocus in young chicks. However, the effect of exogenous cAMP on normal eye growth or lens-induced hyperopia is minimal. This finding indicates that cAMP signalling pathway plays an important role in myopia development and the investigation of its underlying mechanism may help develop novel therapeutic strategies to treat myopia.
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