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H Dolk Environmental Epidemiology Unit, Department of
Public Health and Policy, London School of Hygiene and Tropical
Medicine, London WC1E 7HT
Correspondence to: Dr Dolk
h.dolk{at}lshtm.ac.uk
Objective: To investigate the geographical variation
and clustering of congenital anophthalmia and microphthalmia in England, in response to media reports of clusters.
Design: Comparison of pattern of residence at birth
of cases of anophthalmia and microphthalmia in England in 1988-94, notified to a special register, with pattern of residence of all births. Three groups studied included all cases, all severe cases, and
all severe cases of unknown aetiology.
Outcome measures: Prevalence rates of anophthalmia
and microphthalmia by region and district, and by ward population density and socioeconomic deprivation index of enumeration district grouped into fifths. Clustering expressed as the tendency for the three
nearest neighbours of a case to be more likely to be cases than
expected by chance, or for there to be more cases within circles of
fixed radius of a case than expected by chance.
Results: The overall prevalence of anophthalmia and
microphthalmia was 1.0 per 10 000 births. Regional and district variation in prevalence did not reach statistical significance. Prevalence was higher in rural than urban areas: the relative risk in
the group of wards of lowest population density compared with the most
densely populated group was 1.79 (95% confidence interval 1.15 to
2.81) for all cases and 2.37 (1.38 to 4.08) for severe cases. There was
no evidence of a trend in risk with socioeconomic deprivation. There
was very little evidence of localised clustering.
Conclusions: There is very little evidence to support
the presence of strongly localised environmental exposures causing clusters of children to be born with anophthalmia or microphthalmia. The excess risk in rural areas requires further investigation.
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© BMJ 1998
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