Visual or vision impairment (VI or VIP) is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment, visual impairment may cause the individual difficulties with normal daily tasks, including reading and walking. The terms low vision and blindness are often used for levels of impairment which are difficult or impossible to correct and significantly impact daily life. In addition to the various permanent conditions, fleeting temporary vision impairment, amaurosis fugax, may occur, and may indicate serious medical problems.
The most common causes of visual impairment globally are uncorrected refractive errors (43%), cataracts (33%), and glaucoma (2%). Refractive errors include near-sightedness, far-sightedness, presbyopia, and astigmatism. Cataracts are the most common cause of blindness. Other disorders that may cause visual problems include age-related macular degeneration, diabetic retinopathy, corneal clouding, childhood blindness, and a number of infections. Visual impairment can also be caused by problems in the brain due to stroke, premature birth, or trauma, among others. These cases are known as cortical visual impairment. Screening for vision problems in children may improve future vision and educational achievement. Screening adults without symptoms is of uncertain benefit. Diagnosis is by an eye exam.
The World Health Organization (WHO) estimates that 80% of visual impairment is either preventable or curable with treatment. This includes cataracts, the infections river blindness and trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness. Many people with significant visual impairment benefit from vision rehabilitation, changes in their environment, and assistive devices.
, there were 940 million people with some degree of vision loss. 246 million had low vision and 39 million were blind. The majority of people with poor vision are in the developing world and are over the age of 50 years. Rates of visual impairment have decreased since the 1990s. Visual impairments have considerable economic costs, both directly due to the cost of treatment and indirectly due to decreased ability to work.
Classification
In 2010, the WHO definition for visual impairment was changed and now follows the ICD-11. The previous definition, which used "best corrected visual acuity," was changed to "presenting visual acuity". This change was made as newer studies showed that best-corrected vision overlooks a larger proportion of the population who have visual impairment due to uncorrected refractive errors, and/or lack of access to medical or surgical treatment.
Distance vision impairment: Category 0: No or mild visual impairment – presenting visual acuity better than 6/18 Category 1: Moderate visual impairment – presenting visual acuity worse than 6/18 and better than 6/60 Category 2: Severe visual impairment – presenting visual acuity worse than 6/60 and better than 3/60 Category 3: Blindness – presenting visual acuity worse than 3/60 and better than 1/60 Category 4: Blindness – presenting visual acuity worse than 1/60 with light perception Category 5: Blindness – irreversible blindness with no light perception Near vision impairment: Near visual acuity worse than N6 or M 0.8 at 40 cm.
United Kingdom Severely sight-impaired Defined as having central visual acuity of less than 3/60 with normal fields of vision, or gross visual field restriction. Unable to see at what the normally sighted person sees at .
Sight impaired Able to see at , but not at , what the normally sighted person sees at Registration data does not capture less severe visual impairment, and its prevalence is difficult to quantify
Low vision A visual acuity of less than 6/18 but greater than 3/60. Not eligible to drive and may have difficulty recognising faces across a street, watching television, or choosing clean, unstained, coordinated clothing.Cupples, M., Hart, P., Johnston, A., & Jackson, A. (2011) Improving healthcare access for people with visual impairment and blindness BMJ (Clinical Research Ed.)
In the UK, the Certificate of Vision Impairment (CVI) is used to certify people as being severely sight-impaired or sight-impaired. The accompanying guidance for clinical staff states: "The National Assistance Act 1948 states that a person can be certified as severely sight impaired if they are 'so blind as to be unable to perform any work for which eye sight is essential'". Certification is based on whether a person can do any work for which eyesight is essential, not just one particular job (such as their job before becoming blind).
In practice, the definition depends on individuals' visual acuity and the extent to which their field of vision is restricted. The Department of Health identifies three groups of people who may be classified as severely visually impaired. Those below 3/60 (equivalent to 20/400 in US notation) Snellen (most people below 3/60 are severely sight impaired). Those better than 3/60 but below 6/60 Snellen (people who have a very contracted field of vision only). Those 6/60 Snellen or above (people in this group who have a contracted field of vision, especially if the contraction is in the lower part of the field).
The Department of Health also states that a person is more likely to be classified as severely visually impaired if their eyesight has failed recently or if they are an older individual, both groups being perceived as less able to adapt to their vision loss.
United States In the United States, any person with vision that cannot be corrected to better than 20/200 in the better eye, or who has 20 degrees (diameter) or less of visual field remaining, is considered legally blind or eligible for disability classification and possible inclusion in certain government-sponsored programs.
The terms partially sighted, low vision, legally blind and totally blind are used by schools, colleges, and other educational institutions to describe students with visual impairments. They are defined as follows: Partially sighted indicates some type of visual problem, with a need for the person to receive special education in some cases. Low vision generally refers to a severe visual impairment, not necessarily limited to distance vision. Low vision applies to all individuals with sight who are unable to read the newspaper at a normal viewing distance, even with the aid of eyeglasses or contact lenses. They use a combination of vision and other senses to learn, although they may require adaptations in lighting or the size of print, and, sometimes, braille. Legally blind indicates that a person has less than 20/200 vision in the better eye after best correction (contact lenses or glasses), or a field of vision of less than 20 degrees in the better eye. Totally blind students learn via braille or other non-visual media.
In 1934, the American Medical Association adopted the following definition of blindness:
The United States Congress included this definition as part of the Aid to the Blind program in the Social Security Act passed in 1935. In 1972, the Aid to the Blind program and two others combined under Title XVI of the Social Security Act to form the Supplemental Security Income program which states:
Temporary vision impairment
Vision impairment for a few seconds or minutes may occur due to any of a variety of causes, some serious and requiring medical attention.
Health effects
General functioning Visual impairments may take many forms and be of varying degrees. Visual acuity alone is not always a good predictor of an individual's function. Someone with relatively good acuity (e.g., 20/40) can have difficulty with daily functioning, while someone with worse acuity (e.g., 20/200) may function reasonably well if they have low visual demands.
Best-corrected visual acuity differs from presenting visual acuity; a person with a "normal" best corrected acuity can have "poor" presenting acuity (e.g., an individual who has uncorrected refractive error). Thus, measuring an individual's general functioning depends on one's situational and contextual factors, as well as access to treatment.
The American Medical Association has estimated that the loss of one eye equals 25% impairment of the visual system and 24% impairment of the whole person; total loss of vision in both eyes is considered to be 100% visual impairment and 85% impairment of the whole person.
Some people who fall into this category can use their considerable residual vision – their remaining sight – to complete daily tasks without relying on alternative methods. The role of a low vision specialist (optometrist or ophthalmologist) is to maximize the functional level of a patient's vision by optical or non-optical means. Primarily, this is by use of magnification in the form of telescopic systems for distance vision and optical or electronic magnification for near tasks.
People with significantly reduced acuity may benefit from training conducted by individuals trained in the provision of technical aids. Low vision rehabilitation professionals, some of whom are connected to an agency for the blind, can provide advice on lighting and contrast to maximize remaining vision. These professionals also have access to non-visual aids and can instruct patients in their use.
Mobility Older adults with visual impairment are at an increased risk of physical inactivity, slower gait speeds, and fear of falls.
Physical activity is a useful predictor of overall well-being, and routine physical activity reduces the risk of developing chronic diseases and disability. Older adults with visual impairment (including glaucoma, age-related macular degeneration, and diabetic retinopathy) have decreased physical activity as measured with self-reports and accelerometers. The US National Health and Nutrition Examination Survey (NHANES) showed that people with corrected visual acuity of less than 20/40 spent significantly less time in moderate to vigorous physical activity. Age-related macular degeneration is also associated with a 50% decrease in physical activity–however physical activity is protective against age-related macular degeneration progression.
In terms of mobility, those with visual impairment have a slower gait speed than those without visual impairment; however, the rate of decline remains proportional with increasing age in both groups. Additionally, the visually impaired also have greater difficulty walking a quarter mile (400 m) and walking up stairs, as compared to those with normal vision.
Cognitive Older adults with vision loss are at an increased risk of memory loss, cognitive impairment, and cognitive decline.
Social and psychological Studies demonstrate an association between older adults with visual impairment and poor mental health; discrimination was identified as one of the causes of this association. Older adults with visual impairment have a 1.5-fold risk of reporting perceived discrimination and of these individuals, there was a 2-fold risk of loneliness and 4-fold risk of reporting a lower quality of life. Among adults with visual impairment, the prevalence of moderate loneliness is 28.7% (18.2% in the general population), and the prevalence of severe loneliness is 19.7% (2.7% in the general population). The risk of depression and anxiety is also increased in the visually impaired; 32.2% report depressive symptoms (12.01% in the general population), and 15.61% report anxiety symptoms (10.69% in the general population).
The subjects making the most use of rehabilitation instruments, who lived alone, and preserved their mobility and occupation, were the least depressed, with the lowest risk of suicide and the highest level of social integration.