Biology of the Lens: Lens Transparency as a Function of Embryology, Anatomy, and Physiology

Insights into the biochemical and biophysical mechanisms mediating the longevity of the transparent optics of the eye lens

“…Most fiber cells adjacent and parallel to the meridians must curve slightly, with their posterior and anterior ends facing matching parallel fiber cells from the opposing side of each meridional suture line to fill-in each layer or shell. These are known as "s-shaped" lens fiber cells (41,42). The result is a slight spiral, yet symmetric, organization of lens fiber cells within each cortical layer that could contribute to its accommodative mechanism (43).…”

“…1B). As synchronized cell elongation begins, differentiating lens fiber cells assemble radial growth shells (40)(41)(42). The new growth shells surround previous layers of differentiating fiber cells, increasing the anterior-posterior thickness and lateral diameter of the lens (267,278).…”

“…In fact, nuclei and all membranous organelles, including the endoplasmic reticulum, mitochondria, and Golgi apparatus, are removed during fiber cell differentiation, an advantage for transparency, because whole and fragmented organelles are large enough to scatter light and interfere with image formation (79). The coupled symmetric shells of lens fiber cells and their constituent proteins appear to be stabilized to protect optical function for a lifetime (40)(41)(42). While the significance of symmetry for optical function is obvious (6,40,278,288,(299)(300)(301)(302), continued research into the genetic pathways for coordinated differentiation and establishment of symmetry as well as SRO in vivo is under-researched as an emergent property of lens fiber cells and their tissue-level order.…”

Diabetes and cataracts

“…Behind the anterior lens capsule is a single layer of metabolically active epithelial cells that carry out all normal cellular activities and generate adenosine triphosphate to meet the energy demands of the lens. The epithelial cells differentiate into layers of fibers that form the nucleus, which represent the oldest and most central layers of the lens, and the cortex which represent the outermost and most recently formed layers [17,18].…”

Age-related compaction of lens fibers affects the structure and optical properties of rabbit lenses

“…First, both human and rabbit lenses possess branched suture patterns. However, rabbit lenses feature a "line" suture pattern, whereas human lenses feature a "star" suture pattern (see [ 20 , 21 ] for reviews on lens suture formation.). Thus, rabbit lens fiber arrangement can be considered a simplified version of the more complex fiber organization in human lenses.…”