Between 1984 and 1998, there were 520
240 live births and 518
140 neonatal survivors born to the 4Child
catchment population. A total of 691 eligible children with visual impairment were notified to 4Child
. Of these, 358 (53%) had VI and 323 (47%) had SVI/BL. The total period cumulative incidence of all cases of visual impairment to 12 years of age was 13.3 (95% CI 12.3 to 14.3) per 10
000 live births; for VI it was 7.1 (95% CI 6.4 to 7.8) per 10
000, and for SVI/BL 6.2 (95% CI 5.6 to 6.9). The cumulative incidence of both VI (p
0.04) and SVI/BL (p<0.01) decreased significantly over time (fig 1). The proportion of children with SVI/BL decreased significantly over time (p
0.007) (table 1), whereas the male:female ratio of 1.5:1 did not vary significantly over time. The risk of visual impairment in multiples was twice that of singletons (RR 2.1; 95% CI 1.5 to 2.9) and did not differ by severity. The incidence of both VI and SVI/BL was inversely associated with gestational age (fig 2) and birth weight. Compared with the most recent (1994–1998), the two earlier birth cohorts (1984–1988 and 1989–1993) had higher rates of visual impairments at all gestational ages. Although the proportion of all cases who were preterm was relatively stable at around 30% over time, the incidence of visual impairment overall decreased dramatically over time in this group.
Figure 1Cumulative incidence per 10000 births of visual impairment (VI) and severe visual impairment/blindness (SVI/BL), 3‐year rolling averages, births 1984–1998, Berkshire, Buckinghamshire, Oxfordshire and Northamptonshire. (more ...)
Figure 2Gestational age‐specific cumulative incidence per 10000 live births of visual impairment (VI) and severe visual impairment/blindness (SVI/BL), births 1984–1998, Berkshire, Buckinghamshire, Oxfordshire and Northamptonshire. (more ...)
Overall, 45% of children with VI had isolated visual impairment which varied significantly over time from 39% in the early period to 56% in the later period (p
0.01) (table 2). There was no significant variation over time in the proportion (23%) of children with isolated SVI/BL (p
0.60). Of note, the proportion with cerebral palsy decreased significantly from 39% to 21% among the VI cases (p
0.003) but not among the SVI/BL group (45% overall) (p
Table 2The presence or absence of additional impairments by the severity of visual impairment, Berkshire, Buckinghamshire, Oxfordshire and Northamptonshire, births 1984–1998
The timing of the insult was ascribed to a single category of cause in 89% of all visual impairment cases, while 9% had two causes and 2% had three. The cumulative incidence of both the prenatal causes and the unknown causes associated with cerebral palsy, developmental delay and microcephaly decreased significantly over time (p<0.001) (table 3). Prenatal causes were the commonest single categories for both VI (65%) and SVI/BL (52%) cases. Most of the children (68%) had only one anatomical site involved, 27% had two sites involved and 5% three sites. Cerebral/visual pathways were the most common sites of involvement, affecting 51% of VI cases and 87% of SVI/BL cases. Of the affected very preterm (<33 weeks) infants in the register, 30% had retinopathy of prematurity (ROP) and 80% had impairment of the cerebral/visual pathways. The cumulative incidences in very preterm births were 46.8 (95% CI 32.3 to 65.7) and 126.3 (95% CI 100.2 to 152.4) per 10
000 live births born at <33 weeks, respectively.
The overall incidence of both ROP and cerebral/visual pathway involvement decreased significantly over the three periods (table 4). The cumulative incidence of potentially preventable or treatable visual impairments among all births decreased over time.
Table 4Potentially preventable or treatable visual impairment (VI)* and severe visual impairment/blindness (SVI/BL)†, Berkshire, Buckinghamshire, Oxfordshire and Northamptonshire, births 1984–1998
A total of 130 of the 691 children have subsequently died, with the case fatality being 19% (95% CI 16% to 22%). Their age at death ranged from 4 months to 20 years (median 4 years) and 58% died before reaching their fifth birthday.