It is well known that the survival of babies born prematurely has increased greatly in the recent past and that low birth weight carries a significant morbidity for ophthalmic problems. However, the impact of low birth weight on childhood vision impairment in epidemiological terms is largely unknown.

The article in this issue of the BJO (p 9) by Crofts and colleagues is therefore particularly welcome. Using the Oxford Register of Early Childhood Impairment, these authors gathered information on all babies with severe vision impairment born in the 4 years commencing January 1984. We are told that this population is reasonably representative of the UK as a whole. Vision impairment was defined as an acuity of 6/18 or less in the better eye identified by 5 years of age. From this database the birthweight specific rate of severe vision loss was calculated. The overall rate of severe vision impairment was 1.25/1000 births, but those of birth weight less than 1500 g contributed to 17.5% of the cohort and for this group the rate was 26 times that for babies of 2500–3499 g birth weight. The prevalence of associated impairments was high for all birth weights (60%), but highest for those under 1500 g (72%), decreasing with increasing birth weight to 44% for those over 3500 g.

The time of origin of the disorder …