Optic Nerve Hypoplasia

Prevalence and Epidemiology Along with cortical vision impair­ ment and retinopathy of prematurity, ONH is thought to be one of the most common causes of impaired vision in children under the age of 3 years. It is estimated that 15% to 25% of infants with significant visual impairment have ONH. Reported incidence ranges between 2.4/100,000 residents (<19 years of age) annually in Olmsted County, Minne­ sota, to 17.3/100,000 residents (<18 years of age) annually in Stockholm, Sweden. There is no clear evidence of variation across geographic regions, but a study based in the United Kingdom found higher standardized incidence ratios in inner­city districts of high population density. Risk factors. Although the etiology is unclear in the majority of cases, there are known associations with fetal alco­ hol syndrome, maternal diabetes, and young maternal age. Other risk factors include maternal primiparity, alcohol or drug use by the mother, intrauterine growth restriction, prematurity, and low birth weight.