preschool vision screening program: coverage, validity and outcome

purpose: to evaluate the preschool vision screening program coverage and to assess its validity indices including specificity, negative predictive value (npv), sensitivity and positive predictive value (ppv) and the frequency of treatment for visual impairment. methods: a sample of 906 six-year-old children signed up for primary school registration in the shahrood district (semnan, iran) were randomly selected and invited for optometric examination. mentally retarded and blind subjects due to organic disorders were excluded. all children were examined by optometrists for ocular alignment, visual acuity, cover test, stereoacuity and retinoscopy under cycloplegia. screening history and the results were detected by available documents. treatment history was obtained from the family. results: of 906 invited children, 827 (91.3%) participated in the study, of which 815 (98.6%) were eligible and cooperative. fifty-two children (6.4%) had amblyogenic visual impairment. screening coverage rate was 85.3% (95% confidence interval [ci], 82.9-87.7) which was unrelated to gender, residence in urban or rural area or parents’ education but was greater in families with higher-than-average economic status (87.7% vs 81.9%, p<0.05). the specificity and npv of the screening exam were 95.4% (95%ci, 94.1-96.7) and 96.7% (95%ci, 95.3-98.1), respectively. only 47.5% of children with amblyogenic factors were suspected on screening examination (sensitivity). of those with suspected exams, 38.8% had impairments in optometric examination (ppv). all of those with a correct diagnosis of amblyogenic visual impairment on screening had been treated. conclusion: a significant proportion of six-year-old children have amblyogenic vision impairment. inadequate coverage and validity of the current screening program has prevented timely diagnosis and treatment of many of them.