(Greek: skleros tough, toughen; hard, hardening; dry up)
2. A chronic illness caused by lesions in the white matter of the central nervous system that degenerate the myelin sheath (insulating layer surrounding vertebrate peripheral neurons), marked by a lack of muscle coordination, muscle weakness, speech problems, and abnormal neurological sensations which include: numbness, tingling, burning, prickling, and hyperesthesia (increased sensitivity), and visual impairments.
The cause of multiple sclerosis is unknown, but it is believed to be an autoimmune disorder, in which the body's immune system mistakenly attacks its own tissues as if they were foreign or not supposed to be there.
The symptoms of multiple scleroses vary, depending on which nerves of the brain and spinal cord lose their protective covers.
2. The abnormal formation of new bone in the middle ear that gradually immobilizes the stapes (stirrup bone) and prevents it from vibrating in response to sounds, causing progressive loss of hearing: The deafness caused byotosclerosis may be partially overcome with a hearing aid, but surgery is eventually needed and this involves replacing the stapes bone with a synthetic substitute (stapedectomy).
Also called proliferative endophlebitis, productive phlebitis, venofibrosis, and phlebofibrosis.
At the front of the eyes, the scleras form transparent, domed structures called the corneas which have curved surfaces that serve to focus light coming into the eyes.
As strong as they are, the scleras can be penetrated by sharp objects.
Disease of the sclera is uncommon, however, inflammation of the scleras can occur, usually with a collagen or connective tissue disease caused by rheumatoid arthritis (inflammation in which the joints of the fingers, wrists, toes, or other parts of the body become painful, swollen, stiff, and, in severe cases, deformed), systemic lupus crythematosus (chronic disease that causes inflammation of connective tissues), periarteritis nodosa (disease of small and medium-sized arteries), scleroderma (a disease that can affect many organs and tissues in the body), dermatomycositis (a sometimes fatal disease in which the muscles and skin become inflamed causing weakness of the muscles and a skin rash), and other less clearly defined physical disorders.
The skin may be thickened, hard, and rigid, and pigmented patches may occur.