Visual impairment in Nordic children. I. Nordic registers and prevalence data.

A Nordic study group of ophthalmologists, NORDSYN, has compiled data from registers in Denmark, Finland, Iceland and Norway of 2527 visually impaired children. Each record contains the following information: sex, year of birth, year of registration, classification of visual impairment, ocular diagnosis, systemic diagnosis, aetiology and evt. additional impairments. The ocular diagnoses were compiled into groups, and coding systems for aetiology and additional impairment were developed. The sex distribution revealed a dominance of males compared to the general population at the same age. Cases with non-genetic aetiology showed--through to a lesser extent--the same relative preponderance of males. The diseases in males caused by x-linked genetic factors do, therefore, not fully explain the sex distribution observed in the study. The national prevalences for registration of childhood blindness (WHO-definition: best corrected visual acuity in the best eye less than 3/60 or visual field less than 10 degrees around fixation for the ages 0-15 years) are per 100,000 child-population aged 0-15 years: Denmark 41, Finland 15, Iceland 19 and Norway 15. The differences are primarily presumed to be due to varying efficiency in registration. The proportion of visually impaired children with an additional mobility, hearing or mental impairment is between one-third and one-half of the national materials, thus indicating the need for interdisciplinary tracing of and care for the visually impaired child. This study documents the need of uniform routines for data classification of visually impaired children. The quality of the data in the present study calls for caution in the interpretation of the prevalence estimates. Incidence studies are being prepared to obtain information on whether the amount and causes of visual impairment in children with or without multiple impairments are changing.