Prevalence of visual impairment in adults with intellectual disabilities in the Netherlands: cross-sectional study

Purpose To obtain the first representative and valid population-based prevalence figures on visual impairment and blindness in adults with intellectual disabilities (ID) and to identify risk groups. Methods Study design: Cross-sectional survey. An age-Down's syndrome-stratified random sample of 1598 persons from a base population of 9012 adult users of ID services with mild to profound intellectual disabilities was screened. Participants underwent protocollised on-site screening of visual functions. Results were related to degree of ID, occurrence of Down's syndrome (DS) and age. Main outcome measure: Prevalences of visual impairment and blindness in the study population and in subgroups and weighted prevalences in the total Dutch population using ID services. Results Prevalences of visual impairment ranged from 2.2% (95% confidence interval (CI), 0.5-6.4) in young adults with mild ID and no Down's syndrome to 66.7% (95% CI, 41.0-86.7) in older adults with profound ID and Down's syndrome; prevalences of blindness ranged from 0.7% (95% CI, 0.1-4.1) to 38.9% (95% CI, 28.1-50.3). Weighted prevalences of visual impairment and blindness in the total Dutch population of adult users of intellectual disabity services are 13.8% (95% CI, 9.3-18.4) and 5.0% (95% CI, 3.8-6.2), respectively. Prior to this study, visual impairment or blindness had remained undiagnosed in 106/ 261 (40.6%) persons. Conclusions As compared to published figures for the general Dutch population aged 55 years and over (visual impairment 1.4%, blindness 0.5%), prevalences of visual impairment and blindness are higher in all subgroups with intellectual disabilities, including the young and mildly handicapped group. The diagnosis is too often missed. All persons with severe or profound intellectual disabilities, and all older adults with Down's syndrome, should be considered visually impaired until proved otherwise.