What are visual impairment and blindness.
DEFINITIONS ACCORDING TO THE WHO
According to the World Health Organization (WHO), an individual is considered blind when visual acuity in the best eye is less than 1/20, while the subject is deemed to be visually impaired when this measurement is between 3/10 and 1/20.
This differentiation dates back to around twenty years ago. More specifically, five categories have been defined (International Classification of Diseases - 9th revision):
The first and the second categories concern the visually impaired:
- 1st cat. = visus 3/10-1/10;
- 2nd cat. = visus 1/10-1/20.
The other three categories concern the blind subject:
- 3rd cat. = visus 1/20-1/100 ;
- 4th cat. = visus 1/100-P.L. ;
- 5th cat. = visus off.
In Italy the legal concept of blindness-visual impairment was redefined with the law of 3rd April 2001, no. 138 (“Classification and quantification of visual impairments and norms regarding eye tests”). The innovations introduced by this regulation – promoted in particular by the International Agency for the Prevention of Blindness-IAPB Italy, the Italian Society of Ophthalmological (SOI) and the Italian Union of the Blind and the Partially Sighted (UICI) – have long been hoped for both by health workers and the visually impaired. The main merit of law no.138 is to take into consideration not only central vision but also peripheral vision (the visual field) for the assessment of any eye damage. The previous law (L. 382/70), instead, quantified visual impairment on the basis of a single parameter (visus or visual acuity); so a person affected by retinitis pigmentosa or by glaucoma in an advanced phase (with a visual field reduced to less than 5-10 degrees) paradoxically was not even recognized as visually impaired.
THE MAGNITUDE OF THE PROBLEM
The World Health Organization stresses with insistence that visual impairment/blindness is, at present, a priority issue for Health Services of all countries, whether they are developing or industrialized. In the face of this phenomenon, health services are called to organize programs of intervention, not only preventative and therapeutic, but also and above all, rehabilitative.
The data, or better, the estimates are clear: according to the WHO in 1972, there were just over 10 million blind people in the world; in 1990 the number had risen to 38 million. According to the latest estimates (WHO 2017) there are currently 36 million blind people in the world and 217 million people who can be considered visually impaired: therefore, overall there are 253 million people who have a degree of vision impairment. Even if, in the short and medium term there may be a reduction in this figure, the magazine The Lancet  estimates that, in the long run, the number of blind and visually impaired people is destined to increase. This is basically due to global demographic ageing.
To address these issues, at the end of 2015, IAPB Italy, together with the WHO, organized a major conference aimed at finding a consensus regarding the standards of vision rehabilitation. .
Eighty-one percent of blind or visually impaired people are aged 50 or over. With the increase of the elderly population, more and more people will be at risk of blindness or visual impairment caused by chronic ocular pathologies and the ageing process (related, for example, to retinal degeneration).
In Italy the situation is no less alarming. According to international estimates (2005) the number of blind people stands at 219,174, while the figure for those with visual impairments is at around 1,383,922. This makes for a total of 1,603,096 people who have vision impairment. 
VISUAL IMPAIRMENT: AN EMERGING SOCIAL PROBLEM
Visual impairment is that condition of vision deficit that doesn’t allow an individual the full development of their social and working life activities and the pursuit of their needs and aspirations in life.
All epidemiological studies have shown that the most important risk factor for visual impairment is ageing. Indeed the prevalence of permanent vision impairment increases over time; but after the age of 60, the increase becomes striking and shows a geometric trend. A researcher named Caird had already reported that blindness increased twenty-fold between 65 and 90 years of age. The phenomenon was then confirmed by other major epidemiological studies (National Health and Nutrition Survey; Framinghan Eye Study; Baltimore Eye Survey; Beaver Dam Eye Survey): in subjects aged between 65 and 74 years old there is a prevalence of 0.4-0.8% of blindness while for those who are 75 years old and over the percentage rises to 2.3%.
Visual limitations can be assessed in relation to the inability to perform tasks that are challenging for sight: driving a car, reading, tailoring, communicating with others and working with a computer are all examples of tasks that require good or optimal visual condition. These tasks have become increasingly important in everyday life, not only in industrialized countries, but also in countries that are densely populated (like some Asian countries with rapidly growing economies).
Today the visual requirements needed to be effective and efficient in the workplace and to carry out all our social life tasks are significantly greater than in the past. Eighty-five percent of subjects with an age of over 65 years old who have a visual acuity lower or equal to 6/18, are unable to read standard characters. Eighty-seven percent of subjects with a visual acuity lower than 6/30 have serious difficulties in recognizing faces. Of those subjects with a visual acuity of less than 1/10, half experience difficulty in their movements and 66% encounter difficulties in performing simple tasks (such as dialing a phone number or using a key correctly). It’s therefore evident that the main purpose of the prevention of avoidable sight loss is to ensure levels of functionality that can maintain the capacity for personal autonomy, the possibility of continuing to work and having a social life.
Factsheet by the International Agency for the Prevention of Blindness-IAPB Italy
 Bourne RRA, Flaxman SR, Braithwaite T, Cicinelli MV, Das A, Jonas JB, et al.; Vision Loss Expert Group, "Magnitude, temporal trends, and projections of the global prevalence of blindness and distance and near vision impairment: a systematic review and meta-analysis", Lancet Glob Health. 2017 Sep;5(9):e888–97
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Published on 11 December 2010. Updated on: 13 April 2018.