The lens is a biconvex organ whose shape enables concentration of light and contains a high density of water soluble proteins called crystallins. The lens is comprised of two cell types only; the anterior lens is composed of proliferating cuboidal lens epithelial stem cells. The posterior lens is composed of mature lens fiber cells, which are elongated cells that lack most organelles, including the nucleus. The lens grows throughout life, at a rate that declines with age. The lens capsule is an elastic basement membrane surrounding the lens, and is comprised of collagen produced by the lens epithelium.
Cataract, the most common cause of blindness, is a pathological opacity interfering with the transparency of the lens. It can arise due to mutations in genes essential for lens development and function. It can also be the result of ageing or a symptom of systemic diseases, such as diabetes.