VISUAL IMPAIRMENT IN NORDIC CHILDREN .5. X-LINKED JUVENILE RETINOSCHISIS

In a study on 2,527 visually impaired children from four Nordic countr ies X-linked juvenile retinoschisis was diagnosed in 35 male children. Striking differences in frequency between the four countries were fou nd, with 26 cases reported from Finland, 5 cases from Denmark, and 4 c ases from Norway. None was reported from Iceland. The corresponding ag e and sex-specific prevalence rates of X-linked juvenile retinoschisis (N:1 000 000) were 44.5 in Finland, 8.8 in Denmark, and 7.9 in Norway . The uneven geographical distribution is possibly attributed to a 'fo under effect' due to the settlements in Finland by European immigrants in the 17th century. The visual impairment of the registered cases wa s usually mild with 91.4% falling into WHO category 1. However, one ch ild was totally blind, demonstrating large phenotypic hetergeneity. No ne of our cases had additional impairments. The majority were more tha n five years old, indicating a progressive course during childhood. Ne vertheless, two children were diagnosed at the age of one. The most co mmon age at registration was seven years, coinciding with the beginnin g of school attendance.