Cortex and Nucleus
In the equatorial, or bow, region of the lens, the epithelial cells move centrally, elongate, produce crystalline proteins, lose organelles, and transform into lens fibers. As the lens epithelial cells differentiate, new fibers are continuously laid down over existing fibers, compacting them in a lamellar arrangement. Thus, the outermost fibers, derived from postnatally differentiated lens epithelial cells, are the most recently formed and make up the cortex of the lens, while older layers are located toward the center. The center of the lens contains the oldest fibers, the embryonic and fetal lens nucleus. Lens fibers are densely compacted in the nucleus. Clinically and histologically, the demarcation between the nucleus and cortex is not well defined (see Fig 9-2).
The overall shape of the lens changes over the first decade of life. With increasing age, the diameter of the lens nucleus and cortex increases from anterior to posterior.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.