OBJECTIVE To investigate the modulating effect of neotropics on form deprivation myopia(FDM)in guinea pigs.METHODS Tricolour guinea pigs were randomly divided into normal control group,FDM model group,FDM+saline group,FDM+atropine group,and FDM+neotropine group,with eight animals in each group.Except for the normal control group,the right eyes of the guinea pigs were covered for 14 d to establish a guinea pig FDM model.The drug administration groups were injected with 10 μL of saline,1%atropine,or 1%neotropine into the vitreous cavity once every other day.The changes in the refractive error and axial length of both eyes were recorded for 1 d before the intervention and for 14 d after the intervention.Then,the eyeballs of guinea pigs were taken from the right eyes.HE staining was used to evaluate the histopathological structure of the sclera while sirius red staining was used to detect the collagen protein content in the sclera.RT-qPCR was used to detect the mRNA expressions of transforming growth factor-β1(TGF-β1),matrix metalloproteinase(MMP-2)and tissue inhibitor of metalloproteinase(TIMP-2)in guinea pigs'sclera.The protein expression levels of collagen type Ⅰ(Col-Ⅰ)and TGF-β1 in guinea pig sclera were detected by Western blotting while those of MMP-2,TIMP-2 and Ki-67 were detected by immunohistochemical staining.RESULTS Compared with the nor-mal control group,eyes of guinea pig in the FDM model group showed a significantly lower refractive error(P<0.01),significant elongation of the ocular axis(P<0.01),scattered distribution of scleral fibre bundles,sparse collagen cells,reduced scleral thickness(P<0.01),and a significantly lower collagen protein content(P<0.01).The mRNA and protein expressions of TIMP-2 and TGF-β1 were lower(P<0.05,P<0.01),and MMP-2 was higher(P<0.01)in scleral tissue.The protein expression level of Col-Ⅰwas lower(P<0.05)while that of Ki-67 was elevated(P<0.01)in scleral tissue.Compared with the FDM model group,there were no significant changes in any of the indexes in the FDM+saline group.The refractive error of the right eyes of guinea pigs in the FDM+neotropium group and the FDM+atropium group were significantly higher(P<0.05),the length of the ocular axis was significantly shorter(P<0.05),the collagen fibres were arranged more tightly,the fibre bundles were distributed more orderly,the distribution of the collagen cells was more uniform,and the thickness of the sclera was significantly increased(P<0.01).Collagen protein contents were significantly higher(P<0.05,P<0.01),the mRNA and protein expressions of TIMP-2 and TGF-β1 were significantly higher(P<0.01),MMP-2 mRNA and protein expressions were significantly lower(P<0.05,P<0.01).The protein expression level of Col-Ⅰwas higher(P<0.05,P<0.01),and that of Ki-67 was lower(P<0.05,P<0.01)in scleral tissue.CONCLU-SION The muscarinic antagonist neotropine inhibits the development of myopia in guinea pigs in the FDM model by reversing both the down-regulation of TGF-β1 and the up-regulation of MMP-2 in scleral tissues and inhibiting the remodeling of the scleral extracellular matrix.