Biology of the Transparent Lens and Changes with Age

The significance of growth shells in development of symmetry, transparency, and refraction of the human lens

“…Even though multiple levels of protection (including post-translation modifications, anti-oxidants, and small heat shock proteins) prolong the biological lens for an unusually long functional life, tiny failures at the molecular level and multifactorial, submicroscopic events can slowly and progressively accumulate and disrupt symmetry and order until a “tipping” point is reached ( 11 , 151 – 154 ). The greatest risk factor for loss of transparency is aging of molecular and cellular constituents ( 11 , 24 ). Membrane specializations (projections, protrusions and connections) between fiber cells change with normal lens development and are associated with formation of the symmetric growth shells.…”

“…It is important to emphasize that the coordinated addition of symmetric growth shells of secondary fibers expands the size of the lens and creates a biconvex, biological spheroid that functions as an optical element in the human eye ( Figure 4 ) ( 11 , 19 , 22 – 24 ). The spheroid is defined by an equator separating the anterior from the posterior hemisphere.…”

“…It is formed by concentric shells of symmetric lens fibers ( Figures 2 , 4 , 6 ). Complex, synergistic, and cooperative, often overlapping, signaling pathways promote structural and functional longevity of lens function ( 11 , 24 ) Current research needs to consider interactions within networks of growth factors in the regular and coordinated assembly of new growth shells in the mechanism of lens development.…”