Cataracts, which are areas of opacification in
the lens, have a wide range of causes
The normal lens is composed of a capsule, lens epithelial cells, and a central
mass of tightly packed cells that have lost their nuclei and contain highly
stable transparent proteins termed crystallins.
In cataract formation, there is
degeneration of lens crystallins, which become opaque. Structural changes in the
lens occur with hyaline globules, liquefaction, and focal calcification.
Degenerate lens material may gain access to the aqueous, where it is
phagocytosed by macrophages and may cause blockage of the trabecular meshwork,
leading to secondary open-angle glaucoma.
The main cause of cataracts is thought to be metabolic derangement in lens
nutrition, which is derived from diffusion from the aqueous. There are several
predisposing factors for development. The most common cataracts are those that
develop in ageing (senile cataracts). Predisposing conditions for cataract
formation include trauma, diabetes mellitus, corticosteroid therapy,
inflammation in the globe (e.g. uveitis), glaucoma, and irradiation of the eye.
Congenital cataracts may develop after rubella infection in utero. |
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