A visual impairment prevents us from seeing and interpreting our environment properly.
The causes are diverse: the eyes are not functioning properly, the image is not sent to the brain correctly, the processing of the image signals is not working smoothly, or a combination of these factors. Potential problems are an impaired visual acuity, smaller field of vision, limited perception of depth, colour blindness, poor eye movement, and problems with adjusting to light and darkness.
Severe visual impairments are referred to as ‘low vision’ or ‘blindness’. The degree of vision loss is determined by the visual acuity, after the best optical correction has been provided (glasses or lenses). Disorders affecting other eye functions (movement, depth, colour perception etc.) can also play a role. Eye doctors are the ones who diagnose the visual impairment.
According to the parameters of the World Health Organisation (WHO), blindness refers to a vision of less than or equal to 1/20 in both eyes or a field of vision that is smaller than or equal to 10 degrees. The term low vision is used if you can see less than or equal to 3/10* with both eyes or have a field of vision that is smaller than or equal to 20 degrees. For comparison: a person with good vision has a field of vision of around 180 degrees.