Contributor: Gordon K. Klintworth
Cataracts are a major cause of visual impairment and blindness throughout the world and are the outcome of numerous conditions. Some cataracts are present at birth [cataract - congenital] or appear in infancy or in childhood, but most cataracts in the USA and other western countries are a manifestation of aging [cataract - age related]. Cataractous changes may affect the lens nucleus [cataract - nuclear], lens cortex [cataract - cortical], or subcapsular regions of the lens [cataract - subcapsular]. By the time vision becomes impaired all of these zones of lens may be affected. Senile cataractous lenses [cataract - senile] may be yellowish and even appear brown. Lens opacification has numerous causes and each type of cataract differs in its pathogenesis. Elschnig pearls, which occasionally develop after an extracapsular cataract extraction, reflect an identical proliferation of residual lens epithelial cells. In eyes that are processed after surgical enucleation, as in the presence of uveal melanoma [melanoma - uvea], or at autopsy lens capsule and remnants of the lens cortex are found in the posterior chamber after extracapsular cataract extraction. In some cataractous lenses, such as the cataract of congenital rubella [rubella - congenital], the fibers within the center of the lens retain their nuclei. Cataract in children can cause amblyopia. Morgagnian corpuscles accumulate in these incipient cataracts [cataract - incipient] and the degenerated lens material exerts an osmotic pressure, causing the damaged lens to increase in volume by imbibing water. Such a swollen lens may cause phakomorphic glaucoma [glaucoma - phakomorphic]. The volume of the lens diminishes as a mature cataract becomes a hypermature cataract. After extruded lens material becomes engulfed by macrophages phakolytic glaucoma may develop. The lens fibers in the center of the lens normally harden with aging and produces a simple nuclear sclerotic cataract [cataract - nuclear sclerotic] and may become brown or black. If a morgagnian cataract [cataract - morgagnian] forms, the sclerotic nucleus may sink within the lens by gravity. Cataracts are associated with numerous syndromes including Vici syndrome.