To elucidate changes in the sclera of myopic eyes free of other obvious pathological features, morphometric and ultrastructural studies on the posterior sclera at the foveola of the three lid-fused monkeys that had developed high myopia were performed. The myopic eyes showed increased axial length, and their scleral thickness was about half that of the control eyes. Furthermore, a gradual increase in the size of collagen bundles and fibrils from the inner to the outer layer of the sclera was observed in the control eyes, but was not evident in the myopic eyes. From the present study, it can be speculated that an alteration of fibrillogenesis in the sclera is a key feature of scleral thinning in lid-suture myopia, and that axial elongation of the eyeball results from a combination of altered fibrillogenesis and mechanical expansion.