DISORDERS OF VISION

Disorders of vision affect various parts of the eye. Some disorders are the result of aging, a genetic tendency, or both. Such disorders include glaucoma (increased fluid pressure within the eye), cataract (clouding of the lens), and various retinal problems.

New techniques and medications for detecting and treating glaucoma and cataract have made these two leading causes of blindness very treatable. Today's modern surgical procedures make the treatment of cataracts among the most successful of all operations.

Cataract is a major cause of vision loss worldwide. Almost 20 million people are blind because of this condition. A cataract is a clouding of the normally clear lens of the eye. The clouding of the lens blocks the passage of light needed for sigh. Although a cataract often starts in only one eye, usually both become involved. Cataracts are accompanied by changes in the chemical composition of the lens, but the cause of these alterations is unknown. The signs of cataract are blurred vision, impaired vision at night or in very bright light, and halos around lights. A certain amount of lens clouding occurs in 65% of patient over the age of 50 and 95% of patients over the age of 65. The most effective treatment for cataract is surgical removal.

Glaucomais a group of diseases that can damage the eye's optic nerve and result in vision loss and blindness. However, the group has a single feature in common: progressive damage to the optic nerve due to increased pressure within the eyeball. The risk is much greater for people over 60. The symptoms of glaucoma are blurred vision, usually in one eye, halos appearing around lights, pain in the eye, and loss of peripheral vision. There are several different forms of glaucoma. In general the group of disease is divided into two ones, acute and chronic. Most of these involve the drainage system within the eye. At the front of the eye there is a small space called the

Structure of Eye

the anterior chamber. A clear fluid flows through this chamber and bathes and nourishes the nearby tissues. In glaucoma, for still unknown reasons, the fluid drains too slowly out of the eye. As the fluid builds up, the pressure inside the eye rises. Unless this pressure is controlled, it may cause damage to the optic nerve and other parts of the eye and result in loss of vision. There is no cure for glaucoma. Vision lost from the disease cannot be restored. However, there are treatments (medications and surgery) that may save remaining vision. That is why early diagnosis is important.

STROKE

Stroke is a disease that affects the blood vessels that supply blood to the brain.

A stroke occurs when a blood vessel that brings oxygen and nutrients to the brain bursts or is clogged by a blood clot or some other mass. Because of this rupture or blockage, part of the brain doesn't get the blood and oxygen it needs. Deprived of oxygen, nerve cells in the affected area of the brain can't work and die within minutes. And when nerve cells can't work, the part of the body they control can't work either. The devastating effects of a severe stroke are often permanent because dead brain cells aren't replaced.

There are two main types of stroke. One(ischemic stroke) is caused by blockage of a blood vessel; the other (hemorrhagic stroke) is caused by bleeding. Bleeding strokes have a much higher fatality rate than strokes caused by clots.

The symptoms of stroke can be quite heterogeneous, and patients with the same cause of stroke can have widely differing handicaps. Conversely, patients with the same clinical handicap can in fact have different underlying causes.

Risk factors for stroke include advanced age, hypertension (high blood pressure), previous stroke or TIA (transient ischaemic attack), diabetes mellitus, high cholesterol, cigarette smoking, atrial fibrillation, migraine with aura, and thrombophilia. In clinical practice, blood pressure is the most important modifiable risk factor of stroke; however many other risk factors, such as cigarette smoking cessation and treatment of atrial fibrillation with anticoagulant drugs, are important.

The traditional definition of stroke, devised by the World Health Organisation in the 1970s, is of a 'neurological deficit of cerebrovascular cause that persists beyond 24 hours or is interrupted by death within 24 hours'. This definition was largely devised for the purpose of research and the time frame of 24 hours appears purely arbitrarily chosen as a cut-off point. It divides stroke from TIA (or 'mini-stroke'), which is the same as above but completely resolves clinically within 24 hours. The division of stroke and TIA into separate clinical entities is considered impractical and even unhelpful in practice by many stroke doctors. The main reason for this is the fact that stroke and TIA are caused by the same disease process, and both persons with a stroke or a TIA are at a higher risk of a subsequent stroke.

In recognition of this, and improved methods for the treatment of stroke, the term "brain attack" is being promoted in the Western World as a substitute for stroke or TIA. The new term makes an analogy with "heart attack" (myocardial infarction), because in both conditions, an interruption of blood supply causes death of tissue that is highly time dependent ('time is brain') and potentially life-threatening. Many hospitals have "brain attack" teams within their neurology departments specifically for swift treatment of stroke.