Visual impairment
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.[6] 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.[7][8][9]
"Blindness" redirects here. For other uses, see Blindness (disambiguation).Visual impairment
Vision impairment, vision loss
Uncorrected refractive errors, cataracts, glaucoma[1]
Vision rehabilitation, changes in the environment, assistive devices (eyeglasses, white cane)[2]
940 million / 13% (2015)[5]
The most common causes of visual impairment globally are uncorrected refractive errors (43%), cataracts (33%), and glaucoma (2%).[1] Refractive errors include near-sightedness, far-sightedness, presbyopia, and astigmatism.[1] Cataracts are the most common cause of blindness.[1] Other disorders that may cause visual problems include age-related macular degeneration, diabetic retinopathy, corneal clouding, childhood blindness, and a number of infections.[10] Visual impairment can also be caused by problems in the brain due to stroke, premature birth, or trauma, among others.[11] These cases are known as cortical visual impairment.[11] Screening for vision problems in children may improve future vision and educational achievement.[12] Screening adults without symptoms is of uncertain benefit.[13] Diagnosis is by an eye exam.[2]
The World Health Organization (WHO) estimates that 80% of visual impairment is either preventable or curable with treatment.[1] This includes cataracts, the infections river blindness and trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness.[14] Many people with significant visual impairment benefit from vision rehabilitation, changes in their environment, and assistive devices.[2]
As of 2015, there were 940 million people with some degree of vision loss.[5] 246 million had low vision and 39 million were blind.[1] The majority of people with poor vision are in the developing world and are over the age of 50 years.[1] Rates of visual impairment have decreased since the 1990s.[1] Visual impairments have considerable economic costs both directly due to the cost of treatment and indirectly due to decreased ability to work.[15]
Health effects[edit]
General functioning[edit]
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. It is also important to note that best-corrected visual acuity differs from presenting visual acuity; a person with a "normal" best corrected acuity can have "poor" presenting acuity (e.g. 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.[25]
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;[26][27] total loss of vision in both eyes is considered to be 100% visual impairment and 85% impairment of the whole person.[26]
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 uses.
Mobility[edit]
Older adults with visual impairment are at an increased risk of physical inactivity,[28][29] slower gait speeds,[30][31][32] and fear of falls.[33]
Physical activity is a useful predictor of overall well-being, and routine physical activity reduces the risk of developing chronic diseases and disability.[34][35] 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.[36][37] 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.[38] 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.[39][40]
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.[41]
Social and psychological[edit]
Studies demonstrate an association between older adults with visual impairment and a poor mental health;[43][44][45][46] discrimination was identified as one of the causes of this association.[47] 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.[47] Among adults with visual impairment, the prevalence of moderate loneliness is 28.7% (18.2% in general population) and prevalence of severe loneliness is 19.7% (2.7% in general population).[43] The risk of depression and anxiety are also increased in the visually impaired; 32.2% report depressive symptoms (12.01% in general population), and 15.61% report anxiety symptoms (10.69% in general population).[45]
The subjects making the most use of rehabilitation instruments, who lived alone, and preserved their own mobility and occupation were the least depressed, with the lowest risk of suicide and the highest level of social integration.
Those with worsening sight and the prognosis of eventual blindness are at comparatively high risk of suicide and thus may be in need of supportive services. Many studies have demonstrated how rapid acceptance of the serious visual impairment has led to a better, more productive compliance with rehabilitation programs. Moreover, psychological distress has been reported to be at its highest when sight loss is not complete, but the prognosis is unfavorable. Therefore, early intervention is imperative for enabling successful psychological adjustment.[48]
Associated conditions[edit]
Blindness can occur in combination with such conditions as intellectual disability, autism spectrum disorders, cerebral palsy, hearing impairments, and epilepsy.[49][50] Blindness in combination with hearing loss is known as deafblindness.
It has been estimated that over half of completely blind people have non-24-hour sleep–wake disorder, a condition in which a person's circadian rhythm, normally slightly longer than 24 hours, is not entrained (synchronized) to the light–dark cycle.[51][52]
Prevention[edit]
The World Health Organization estimates that 80% of visual loss is either preventable or curable with treatment.[1] This includes cataracts, onchocerciasis, trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness.[14] The Center for Disease Control and Prevention estimates that half of blindness in the United States is preventable.[2]
Epidemiology[edit]
The WHO estimates that in 2012 there were 285 million visually impaired people in the world, of which 246 million had low vision and 39 million were blind.[1]
Of those who are blind 90% live in the developing world.[77] Worldwide for each blind person, an average of 3.4 people have low vision, with country and regional variation ranging from 2.4 to 5.5.[78]
By age: Visual impairment is unequally distributed across age groups. More than 82% of all people who are blind are 50 years of age and older, although they represent only 19% of the world's population. Due to the expected number of years lived in blindness (blind years), childhood blindness remains a significant problem, with an estimated 1.4 million blind children below age 15.
By gender: Available studies consistently indicate that in every region of the world, and at all ages, females have a significantly higher risk of being visually impaired than males.[79][80][81][82][83][84]
By geography: Visual impairment is not distributed uniformly throughout the world. More than 90% of the world's visually impaired live in developing countries.[78]
Since the estimates of the 1990s, new data based on the 2002 global population show a reduction in the number of people who are blind or visually impaired, and those who are blind from the effects of infectious diseases, but an increase in the number of people who are blind from conditions related to longer life spans.[78]
In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness.[85] Of this number, 58% were over the age of 65.[85] In 1994–1995, 1.3 million Americans reported legal blindness.[86]