Primary Lens Fibers and the Embryonic Nucleus
The cells in the posterior layer of the lens vesicle stop dividing and begin to elongate between 33 and 35 days of gestation. As they elongate, they begin to fill the lumen of the lens vesicle. At approximately 40 days of gestation, the lumen of the lens vesicle is obliterated. The elongated cells are called the primary lens fibers. As the fiber cells mature, their nuclei and other membrane-bound organelles undergo degradation, a process that reduces light scattering. The primary lens fibers make up the embryonic nucleus that will ultimately occupy the central area of the adult lens.
The cells of the anterior lens vesicle give rise to the lens epithelium, a monolayer of cuboidal cells. Proliferation within the epithelium causes subsequent growth of the lens. The lens capsule develops as a basement membrane elaborated by the lens epithelium anteriorly and by lens fibers posteriorly.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.