Prepared August 2017, updated October 2020
Functional limitation refers to the interaction of visual functioning and ability to perform activities of daily living/instrumental activities of daily living. Daily activities potentially affected by vision loss are reading, safe pedestrian travel, self-care, cooking, and recreational activities.
Legal blindness is a level of vision loss that has been legally defined to determine eligibility for benefits. In the United States, this refers to a medically diagnosed central visual acuity of 20/200 or less in the better eye with the best possible correction, and/or a visual field of 20 degrees or less. See the Blue Book Disability Evaluation Under Social Security. Often, people who are diagnosed with legal blindness still have some usable vision.
Low vision describes "a person who has measurable vision but has difficulty accomplishing or cannot accomplish visual tasks even with prescribed corrective lenses but who can enhance his or her ability to accomplish these tasks with the use of compensatory visual strategies, low vision devices, and environmental modifications" (Corn & Lusk, 2010, p. 4-5).
Total blindness refers to an inability to see anything with either eye.
Vision loss refers to individuals who have trouble seeing, even when wearing glasses or contact lenses, as well as to individuals who are blind or unable to see at all.
Visual acuity is the "measure of an eye's ability to distinguish object details and shape, [it is] typically assessed by the smallest identifiable object that can be seen at a specified distance (usually 20 feet or 16 inches)" (Cassin, , p. 24). Typical vision is 20/20. If an individual sees 20/200, the smallest letter that this individual can see at 20 feet could be seen by someone with typical vision at 200 feet.
Visual impairment/visual disability is "a term that encompasses both those who are blind and those with low vision" (Corn & Lusk, 2010, p. 13). Additional factors influencing visual impairment might be contrast sensitivity, light sensitivity, glare sensitivity, and light/dark adaptation.
Frequency is the number of people who were similar for a given characteristic within a given time period. For example, in 2015, 23.7 million adult Americans reported vision loss.
Prevalence is a measurement of the proportion of individuals in a population affected by a condition within a particular period of time. Prevalence indicates how widespread a condition is. Prevalence is typically expressed as a percentage. For example, according to the 2014 National Health Interview Survey, 14.5% of adults (ages 18 and up) with vision difficulty also experienced difficulty hearing.
Incidence is a measurement of the number of new individuals who develop a condition during a particular period of time. Incidence conveys information about the risk of developing the condition. For example, the incidence of retinopathy of prematurity "varies with birth weight but is reported to be approximately 50-70% in infants whose weight is less than 1250 g at birth" (Subramanian, 2015).
When discussing employment, there are four commonly used figures: unemployment rate, labor force participation rate, percentage not in the labor force, and employment-population ratio. Since it would be impossible to count and identify everyone who is employed and unemployed in the United States at a single point in time, these figures are reported as estimates, usually based on a survey of a randomly sampled portion of the population.
The unemployment rate, as calculated by the Bureau of Labor Statistics (BLS), is the percentage of the total labor force that is unemployed but actively seeking employment and willing to work. Since the unemployment rate is calculated as a fraction of the labor force, it does not count individuals who are considered "not in the labor force" - those who are not looking for work, whether they never sought employment, they left the workforce for retirement, or they dropped out of the workforce because of disability or long-term unemployment (Bureau of Labor Statistics, 2017).
The labor force participation rate, as defined by the BLS, is "the percentage of the population that is either employed or unemployed (that is, either working or actively seeking work)" (Bureau of Labor Statistics, 2014).
The percentage not in the labor force accounts for the proportion of the total population (ages 16 and up) that has either dropped out of the labor force or never entered it. This number is typically higher than the unemployment rate and, when added to the unemployment rate, provides a more accurate picture of the proportion of people who are not employed (Bureau of Labor Statistics, 2017).
The employment-population ratio (commonly confused with the employment rate) is the percentage of the total population that is employed, where the total population includes people working, people actively seeking work, and people who have dropped out of the labor force or never entered it (Bureau of Labor Statistics, 2016).
As a reminder, the Census Bureau and BLS determine these estimates for the civilian, non-institutionalized population.
Cassin, B. (2006). Dictionary of eye terminology (5th ed.). Gainesville, Florida: Triad Publishing Company.
Corn, A. L, & Lusk, K. E., (2010). Perspectives on low vision. In A.L. Corn & J.N. Erin (Eds.), Foundations of low vision: Clinical and functional perspectives (2nd ed.) (pp. 3-34). New York, New York: AFB Press.