Performance measures of the illiterate E-chart vision-screening test used in Northern District Israeli school children

Objectives: To evaluate the screening performance of 6/6 and 6/12 vision cut-offs with an illiterate E-chart implemented by a public health nurse to test children for ocular abnormalities and uncorrected refractive error. The gold standard diagnosis is an eye examination performed by an ophthalmologist. Setting: A cross-sectional population-based study was conducted among 2113 students' ages 6-7 and 13-14 years old in 70 Northern District Israeli schools. Methods: Students were tested by nurses and ophthalmologists. A nurse examination was carried out using the illiterate E-chart for vision measurement. The medical examination included vision history, clinical eye examination, vision and retinoscopy testing. The Physician's evaluation of whether students needed a referral for diagnostic procedures, treatment and/or follow-up was recorded. Screening test's performance was determined using ophthalmologist's decision regarding referral as the gold standard. Detection rate (DR), false-positive rate (FPR), odds affected positive result (OAPR), positive predictive value (PPV) and negative predictive value (NPV) were estimated overall and by students' demographic characteristics. Results: For vision >6/6 cut-off in at least one eye (eyes tested separately): DR - 71.9% (95% CI 65.8-78.7%), FPR - 22.8% (95% CI 17.9-28.9%), OAPR - 0.98:1 (95% CI 0.84:1-1.15:1), PPV - 52.7% (95% CI 45.4-61.2%), NPV - 90.9% (95% CI 88.7-93.1%). For 6/12 vision cutoff, namely vision 6/12 or worse in both eyes (tested separately): DR - 58.6 (95% CI 51.8-66.4%), FPR - 15.2% (95% CI 10.9-21.1%), OAPR - 1.13:1 (95% CI 0.94:1-1.35:1), PPV - 61.1% (95% CI 52.9-70.6%), NPV - 87.6% (95% CI 84.9-90.4%). Conclusions: Vision-screening test performance measures are mild. It is suggested to change vision cut-off level that denotes vision abnormality from current policy of vision not equal 6/6 in both eyes (tested separately) to vision 6/12 or worse in both eyes (tested separately). This change will result in reduction of FPR from 22% to 15%, concomitant with an increase in false-negative rate from 28% to 41%. Students may be equally screened by either a senior or a less experienced nurse.