OXIDATIVE STRESS
Free radicals are generated both by UVR absorption
and by cellular metabolic processes. Oxidative stress
results when the rate of free radical production is
greater than the rate of their degradation. Oxidative
stress can impair the structure and function of connexins
(gap junction proteins), can modify lens crystallins,
and can cause aggregation of proteins, all of
which contribute to cataract development.77 Glutathione
is a reducing agent that detoxifies free radicals,
thus preventing such damage. It is found in high concentration
within the
lens and the
aqueous humor and
is transported into the lens from the aqueous. It can
be synthesized and regenerated by the lens epithelial
cells and young lens fibers.68 The deeper fibers rely
on diffusion of glutathione from superficial fibers.78
Glutathione also has a role in maintaining membrane
transport mechanisms.78
Ascorbic acid also provides some protection to lens
epithelium against UV-induced damage to deoxyribonucleic
acid (DNA) and is present in relatively high levels
in the aqueous humor.79