Impaired vision, blindness

What are impaired vision and blindness?

The WHO definition of impaired vision is that visual acuity (after correction!) is less than 0.3 but more than 0.05 or that the field of vision is less than 30 degrees ('tunnel vision') but more than 10 degrees. People are considered to be blind when their visual acuity is less than 0.05 or their field of vision is less than 10 degrees. The categories used for vision are: ⁵⁰⁶

What are the complaints associated with impaired vision and blindness?

Impaired vision can have a range of consequences, including: more blurred vision, limited field of vision (which often leads to problems with tracking), limited depth perception, limited colour perception, and limited ability to adjust to changes in light levels. Being blind or partially sighted can cause problems with communication (missing non-verbal information) and with safety, orientation, reading, writing and the use of certain objects. The consequences of visual impairment vary from person to person and they depend on how people cope with it. There are additional complaints in people with intellectual disabilities: behaviour problems, uncertain gait and, in people with severe or very severe intellectual disabilities, a slight reduction in ADL skills. ^{188 , 507 , 508}

There have been no studies of the relationship between visual impairment and behaviour problems looking at which causes the other. On the one hand, impaired vision may explain challenging behaviour since it could cause problems with communication. On the other hand, visual impairment may be caused by behaviour problems (such as eye damage caused by self-injurious behaviour). ¹⁸⁹

How common are impaired vision and blindness in the general population?

Impaired vision is found in 1.4% of the general Dutch population aged 55 and over, and blindness in 0.5%. ¹⁹⁰

How common are impaired vision and blindness in people with intellectual disabilities?

A major Dutch prevalence study of 1598 adults with intellectual disabilities found visual impairment in 13.5% and blindness in 5.7%. ¹⁹¹

Impaired vision or blindness are twelve times more common in people with intellectual disabilities than in the general population. The prevalence rates are higher in Down syndrome, in people over 50 and in people with severe intellectual disabilities.

An Australian survey of 2540 people with intellectual disabilities (in which questionnaires were answered by carers and parents) found that 38% of the study sample had impaired vision. ¹⁹²

Visual impairment is found in 62% to 71% of people with cerebral palsy. ¹⁹³