Ultrastructural study of the developing mouse vitreous body.

The ultrastructure of the developing mouse vitreous body was studied at prenatal (10-to 18-day embryos) and postnatal (1 day, 4 days, 1, 2, 2.5 weeks after birth) stages. Characteristic changes allow a subdivision of the developmental period into four successive phases. A thickening of the lens basement membrane and the presence of many mesenchymal cells in the vitreous space characterize the first phase. During the second phase, a continuous basement membrane is being laid down around the hyaloid capillaries, zonular fibres appear in close contact with the lens capsule and retinal basement membrane, a very dense afibrillar material begins to fill up the lens periequatorial area. During the third phase, the perivascular membrane and the ciliary body basement membrane become multilayered and redundant and the periequatorial material and posterior granular substance become denser. During the latest phase the periequatorial material is vanishing, the hyaloid capillaries disappear, the density of the posterior granular substance decreases. The results do not confirm the existence of a clear distinction between primary and secondary vitreous at the ultrastructural level. The study reveals a transient accumulation of a very dense afibrillar material in the periequatorial area during development. Its nature and significance remain unknown.