To assess anatomical changes in eyes with progressive myopia, we morphometrically examined the eyes of guinea pigs with lens-induced axial elongation. Starting at an age of 3-4 weeks, guinea pigs in the experimental group (n = 20 animals) developed unilateral lens-induced axial elongation by wearing goggles for 5 weeks compared to a control group of 20 animals without intervention (axial length: 8.91 +/- 0.08 mm versus 8.74 +/- 0.07 mm; P < 0.001). Five weeks after baseline, the animals were sacrificed, and the eyes enucleated. As measured histomorphometrically, Bruch's membrane thickness was not significantly correlated with axial length in either group at the ora serrata (P = 0.41), equator (P = 0.41), midpoint between equator and posterior pole (MBEPP) (P = 0.13) or posterior pole (P = 0.89). Retinal pigment epithelium (RPE) cell density decreased with longer axial length at the MBEPP (P = 0.04; regression coefficient beta = -0.33) and posterior pole (P = 0.01; beta = -0.40). Additionally, the thickness of the retina and sclera decreased with longer axial length at the MBEPP (P = 0.01; beta = -0.42 and P < 0.001; beta = -0.64, respectively) and posterior pole (P < 0.001; beta = -0.51 and P < 0.001; beta = -0.45, respectively). Choroidal thickness decreased at the posterior pole (P < 0.001; beta = -0.51). Experimental axial elongation was associated with a thinning of the retina, choroid and sclera and a decrease in RPE cell density, most markedly at the posterior pole. Bruch's membrane thickness was not related to axial elongation.