The contemporary conception of disability proposed in the WHO International Classification of Functioning, Disability and Health (ICF) views disability as an umbrella term for impairments, activity limitations and participation restrictions. Disability is the interaction between individuals with a health condition (e.g. cerebral palsy, Down syndrome or depression) and personal and environmental factors (e.g. negative attitudes, inaccessible transportation, or limited social supports).
Long ago there was great confusion over the meaning of terms such as impairment, handicap, or disability. Then, in 1980, the WHO provided great service by offering a clear way of thinking about it all in a little book called "International Classification of Impairments, Disabilities and Handicaps".
All these terms refer to the consequences of disease, but consider the consequences at different levels. The disease produces some form of pathology, and then the individual may become aware of this: they experience symptoms. Later, the performance or behaviour of the person may be affected, and because of this the person may suffer consequences such as being unable to work. In this general scenario,
Impairment was defined as "any loss or abnormality of psychological, physiological, or anatomical structure or function." Impairment is a deviation from normal organ function; it may be visible or invisible (screening tests generally seek to identify impairments).
Disability was defined as "any restriction or lack (resulting from an impairment) of ability to perform an activity in the manner or within the range considered normal for a human being." Impairment does not necessarily lead to a disability, for the impairment may be corrected. I am, for example, wearing eye glasses, but do not perceive that any disability arises from my impaired vision. A disability refers to the function of the individual (rather than of an organ, as with