1. Sorsby, A. & Leary, G. A. Refraction and its components in twins. Special Report Series no. 303 (Medical Research Council, 1962).
2. Young, F. A. et al. Am. J. Optom. Arch. Am. Acad. Optom. 46, 676–685 (1969).
3. Salinas, D. Does Homework Perpetuate Inequities in Education? (OECD, 2014). Available at
http://doi.org/2sd
4. Zylbermann, R., Landau, D. & Berson, D. J. Pediatr. Ophthalmol. Strabismus 30, 319–322 (1993).
5. Saw, S. M., Carkeet, A., Chia, K. S., Stone, R. A. & Tan, D. T. Ophthalmology 109, 2065–2071 (2002).