Footnotes

• For the British Childhood Visual Impairment Interest Group (see Appendix)

• Funding The study was supported by grants from the British Council for Prevention of Blindness, Children Nationwide and the National Eye Research Centre. This work was undertaken at the Great Ormond Street Hospital/UCL Institute of Child Health that received a proportion of its funding from the Department of Health's National Institute of Health Research Biomedical Research Centres funding scheme. The Centre for Paediatric Epidemiology and Biostatistics also benefits from the funding support from the Medical Research Council in its capacity as the MRC Centre of Epidemiology for Child Health. JSR holds a joint appointment with Moorfields Eye Hospital/Institute of Ophthalmology, University College London, that also received a proportion of its funding from the Department of Health's National Institute of Health Research Biomedical Research Centres funding scheme. PMC is supported by the Ulverscroft Foundation.

• Competing interests None.

• Ethics approval This study was conducted with the approval of the Institute of Child Health/Great Ormond Street Hospital local research ethics committee, and the data were handled in accordance with extant guidance on data protection.

• Provenance and peer review Not commissioned; externally peer reviewed.