Retinoic acid metabolic change in retina and choroid of the guinea pig with lens-induced myopia

AIM: To investigate the role of retinoic add (RA) and retinaldehyde dehydrogenase-2 (RALDH(2)) of retina and choroid in the guinea pig lens-induced myopic eyes. METHODS: Totally 45 guinea pigs, at age of three weeks, were randomly assigned into three groups: the normal control, the lens-induced group and the recovering group. Out of focus was induced by the -6.00D concave lens on the left eye, and lasted for 15 days. All animals underwent biometric measurement (corneal radius of curvature, refraction and axial length). Subsequently, RA content in the retina and RPE/choriod complex was detected by reversed-phase high-performance liquid chromatography. RALDH(2) protein in the retina and RPE/choriod complex was evaluated by the immunohistochemical staining and Western blotting. RESULTS: After wearing -6.00D lens for 15 days, axial length of the lens-induced eye extends and myopia was formed, with RA contents increasing in both the neural retina and RPE/choroid complex. Comparing with the lens-induced group, myopic degree significantly relieved, and its RA contents in both the neural retina and RPE/choroid complex decreased in the recovering group. In the normal control, RALDH(2) protein was expressed positively in the retinal nerve fiber layer (RNFL), inner plexiform layer (IPL) and lateral border of outer nuclear layer (ONL). Retinal RALDH(2) protein increased in the lens-induced group, and was also positive in the outer plexiform layer (OPL). In the recovering group, retinal RALDH(2) protein attenuated the expression in the OPL turns to negative. RALDH(2) protein was not expressed in the choroid of any group. CONCLUSION: RA of retina and chorid participates in the regulation of the lens-induced myopia in guinea pigs, which may be related with retinal RALDH(2) protein.

Comparison of form-deprived myopia and lens-induced myopia in guinea pigs

AIM:To study the efficacy difference between formdeprived myopia(FDM)and lens-induced myopia(LIM),the degree of myopia,axial length and pathological changes of the posterior sclera from guinea pigs were evaluated.METHODS:Four-week pigmented guinea pigs were randomly assigned into 3 groups,including normal control(n=6),FDM group with monocular cover(n=11)and LIM group with monocular-7D lens treatment(n=11).FDM group was form-deprived while LIM group was lens-induced for 14d.Refractive error and axial length were measured prior to and post treatment,respectively.Morphological changes of sclera were examined using both light and electronic microscopes.RESULTS:After 14d treatment,refractive errors for FDM group and LIM group were-3.05±0.71D and-2.12±1.29D,respectively,which were significantly more myopic than that of normal controls and fellow control eyes(P【0.01).As for axial length,it was 7.93±0.03 mm for FDM group and 7.89±0.06 mm for LIM group,which were significantly longer than both normal and fellow controls(P【0.01).With respect to both refractory error and axial length,the differences between FDM group and LIM group were not significant(P】0.05).Under light microscope,both FDM group and LIM group showed thinned sclera,disarrangement of fibrosis and enlargeddisassociation between fibers.Consistently,ultrastructural examination showed degenerated fibroblasts and thinned fibers in posterior sclera.CONCLUSION:Following two weeks of myopia induction in guinea pigs,with regard to the degree of myopia,axial length and pathological alterations,there was no significant difference between FDM and LIM models.Therefore,FDM and LIM are equally effective and useful as a model of experimental myopia and guinea pigs are ideal animals for induction of experimental myopia because their high sensitivity to both formdeprivation and lens-induction.