Nucleus and Cortex
As new fibers are laid down, no cells are lost from the lens. The new fibers crowd and compact the previously formed fibers; the older layers are located toward the center. The oldest layers, the embryonic and fetal lens nuclei, were produced during embryogenesis and persist in the center of the lens (see Chapter 4, Fig 4-1). The outermost fibers are the most recently formed and make up the cortex of the lens.
Lens sutures (see Chapter 4, Fig 4-1) are formed by the interdigitation of the anterior and posterior tips of the spindle-shaped fibers. Multiple optical zones, as well as Y-shaped sutures located within the lens nucleus, are visible on slit-lamp biomicroscopy. (See Chapter 4 in this volume for further discussion of the embryonic nucleus and lens sutures.)
Strata of epithelial cells with differing optical densities are laid down throughout life, creating the zones of demarcation between the cortex and the nucleus. However, there is no morphologic distinction between the cortex and the nucleus; rather, the transition between these regions is gradual. Although some surgical texts and this volume make distinctions between the nucleus, epinucleus, endonucleus, and cortex, these terms relate only to potential differences in the behavior and appearance of the material during surgical procedures.
Kuszak JR, Clark JI, Cooper KE, et al. Biology of the lens: lens transparency as a function of embryology, anatomy and physiology. In: Albert D, Miller J, Azar D, Blodi B, eds. Albert & Jakobiec’s Principles and Practice of Ophthalmology. 3rd ed. Saunders; 2008: vol 1, chapter 104.
Snell RS, Lemp MA. Clinical Anatomy of the Eye. 2nd ed. Blackwell Science; 1998: 197–204.
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.