Validation of night blindness reports among children and women in a vitamin A deficient population in rural Tanzania.

OBJECTIVE: This study validates different definitions of reported night blindness (XN) in a vitamin A deficient African population with no local term for XN. DESIGN: Case-control study with follow-up after treatment. SETTING: Eight primary schools and health centres in rural Tanzania. SUBJECTS: A total of 1214 participants were screened for reported XN and other eye signs of xerophthalmia: 461 children aged 24-71 months, 562 primary school-age children and 191 pregnant or breast-feeding women. All 152 cases of reported XN were selected for the validation study and group matched with 321 controls who did not complain of XN. XN reports were validated against serum retinol concentrations and pupillary dark adaptation measurements in cases and controls. INTERVENTION: All children and women who reported XN or had other signs of active xerophthalmia were treated with vitamin A and followed up 3-4 weeks later. Half of the untreated control group who had their serum retinol examined in the baseline examination were also followed up. RESULTS: The overall prevalence of reported XN was 12.5%. At baseline, mean pupillary threshold (-1.52 vs -1.55 log cd/m(2), P=0.501) and median serum retinol concentrations (0.95 vs 0.93 micromol/l, P=0.734) were not significantly different in cases and controls either overall or in each population group. More restricted case definitions reduced the prevalence of reported XN to 5.5% (P<0.001), but there was still no significant difference between cases and controls although the results were in the expected direction. After treatment, the median serum retinol concentration improved significantly only in the most deficient group, the young children. Dark adaptation improved in all the subgroups but the difference was only significant for young children and primary school-age children when the restricted case definitions were used. CONCLUSIONS: XN reports are a poor indicator of vitamin A deficiency in this population. SPONSORSHIP: Task Force Sight and Life, Basel, Switzerland.

Myopia in secondary school students in Mwanza City, Tanzania: the need for a national screening programme.

BACKGROUND/AIMS: The prevalence of significant refractive errors and other eye diseases was measured in 2511 secondary school students aged 11-27 years in Mwanza City, Tanzania. Risk factors for myopia were explored. METHODS: A questionnaire assessed the students' socioeconomic background and exposure to near work followed by visual acuity assessment and a full eye examination. Non-cycloplegic objective and subjective refraction was done on all participants with visual acuity of worse than 6/12 in either eye without an obvious cause. RESULTS: 154 (6.1%) students had significant refractive errors. Myopia was the leading refractive error (5.6%). Amblyopia (0.4%), strabismus (0.2%), and other treatable eye disorders were uncommon. Only 30.3% of students with significant refractive errors wore spectacles before the survey. Age, sex, ethnicity, father's educational status, and a family history of siblings with spectacles were significant independent risk factors for myopia. CONCLUSION: The prevalence of uncorrected significant refractive errors is high enough to justify a regular school eye screening programme in secondary schools in Tanzania. Risk factors for myopia are similar to those reported in European, North-American, and Asian populations.

Prevalence of eye diseases in primary school children in a rural area of Tanzania.

AIMS: The study measured the prevalence of eye diseases in primary school children between 7 and 19 years of age in a rural area of Tanzania, and investigated whether teachers could successfully provide the first component of a school eye screening service. METHODS: Teachers from each of three primary schools in Mwanza Region tested visual acuity using a Snellen's E chart in 1438 pupils. 1386 of these pupils were then interviewed and underwent a full eye examination by an eye team. RESULTS: 10 pupils (0.7%) had bilateral poor eyesight (visual acuity worse than 6/12), and an additional 14 pupils (1.0%) had unilateral poor eyesight. Significant refractive errors causing visual acuity less than 6/12 (1.0%), strabismus (0. 5%), and amblyopia (0.2%) were uncommon. Overall, 76 pupils (5.5%) had active trachoma, though the prevalence was 15.5% in the poorest school. 73 pupils (5.3%) reported night blindness, eight (0.6%) had Bitot's spots, and 11 (0.8%) had corneal scars. Simple screening by teachers correctly identified 80% of the pupils who were found to have bilateral poor eyesight by the eye team, with 91% specificity. CONCLUSION: The prevalence of significant refractive errors was not high enough to justify a school eye screening programme solely for this purpose. However, a programme may be justified in areas where trachoma is common. Further research is needed to validate the frequent reports of night blindness and to establish the public health importance of vitamin A deficiency in this age group.