Dictionary

blindness, river See river blindness.

blindness, night See nyctanopia

blindness, legal A degree of blindness that entitles a person to certain benefits according to the law. The definition of legal blindness varies from country to country. In the US, the definition of legal blindness that is used to determine eligibility for government disability benefits is as follows: 1 visual acuity of 20/200 or worse…

blindness Loss of useful sight. Blindness can be temporary or permanent, and there are many causes of blindness. Damage to any portion of the eye, the optic nerve, or the area of the brain that is responsible for vision can lead to blindness. Also known as visually handicapped, visually impaired, and visually challenged. See also…

blinded study A clinical trial of drugs in which the test participants do not know whether they are receiving the product being tested or a placebo (dummy). This blinding is intended to ensure that the study results are not affected by the power of suggestion (the placebo effect). See also doubleblinded study.

blind Unable to see. See also blindness.

blighted ovum A fertilized ovum (egg) that did not develop or whose development ceased at an early stage, before 6 or 7 weeks of gestation. On the ultrasound examination of a blighted ovum, only the gestational sac that normally surrounds the embryo can be seen. There is usually no embryo inside the gestational sac. A…

blepharospasm The involuntary, forcible closure of the eyelids. The first symptoms may be uncontrollable blinking. Only one eye may be affected initially, but eventually both eyes are usually involved. The spasms may leave the eyelids completely closed, causing functional blindness even though the eyes and vision are normal. Blepharospasm is a form of focal dystonia.

blepharitis Inflammation of the eyelids. Blepharitis occurs in two forms, anterior and posterior. Anterior blepharitis affects the outside front of the eyelid, where the eyelashes are attached. The two most common causes of anterior blepharitis are bacteria (Staphylococcus) and scalp dandruff. Posterior blepharitis affects the inner eyelid (the moist part that makes contact with the…

bleeding Hemorrhaging. Losing blood, typically because of injury to blood vessels. With simple bleeding, cleaning the site of injury and applying mild pressure or a bandage is sufficient treatment. If bleeding is caused by injury to a major blood vessel, emergency care is necessary. Spontaneous bleeding in the skin can represent a serious underlying illness…

bleb See blister.

blastoma A tumor thought to arise in embryonic tissue. This term is commonly used as part of the name for a tumor, as in glioblastoma and medulloblastoma (types of brain tumors), hepatoblastoma (a liver tumor), nephroblastoma (a Wilms tumor of the kidney), neuroblastoma (a childhood tumor of neural origin), osteoblastoma (a bone tumor), and retinoblastoma…