BackgroundLens-induced myopization in guinea pigs has been used as model for the process of myopization in humans. It has not been explored yet whether the change in globe shape in eyes undergoing myopization is similar in experimental myopia in guinea pigs and in clinical myopia in patients.MethodsThe study included 70 guinea pigs (age:2-3weeks) equally divided into a study group with lens-induced myopization for 5weeks, and a control group wearing goggles with no refractive power. The globe diameters were measured using a microcaliper after enucleation.ResultsThe horizontal globe diameter (9.190.15mm versus 9.15 +/- 0.18mm; P=0.25) and vertical globe diameter (9.02 +/- 0.11mm versus 8.99 +/- 0.14mm; P=0.29) did not differ significantly between the study group and control group. The sagittal diameter was significantly longer in the study group (8.96 +/- 0.15mm versus 8.84 +/- 0.14mm; P=0.001). While the vertical and horizontal globe diameters were correlated with each other in a ratio of approximately 1:1 (non-standardized regression coefficient B:0.94;95% confidence interval (CI):0.73,1.15), the steepness of the regression lines of the associations of both diameters with the sagittal diameter were flatter (horizontal to sagittal diameter: B: 0.64; 95% CI: 0.44,0.83; vertical to sagittal diameter:B:0.55;95% CI:0.41,0.69). Correspondingly, the ratios of horizontal-to-sagittal globe diameter and of vertical-to-sagittal globe diameter decreased (P<0.001) with longer sagittal diameter.Conclusions For each mm axial elongation in young guinea pigs the horizontal globe diameter increased by 0.64mm (95%CI:0.44,0.83) and the vertical diameter by 0.55mm (95% CI:0.41,0.69), indicating that the globe enlargement occurred predominantly in the sagittal direction. Axial elongation in guinea pigs led to a similar relative change in ocular shape as in humans.