We acquired child and parent refraction information as part of a 24-year longitudinal study of visual development in children. These children were research subjects and are not a clinical population. Refractions from 213 children and their parents are included; all children were refracted in the laboratory by non-cycloplegic retinoscopy.

One limitation of Quinn et al.'s study is a lack of information about the refractive status of the parents. Parents in our study were either tested in the laboratory or their spectacle prescriptions were used; if they had never worn glasses and could see clearly at a distance, they were classed as non-myopic.

Subjects (100 females and 113 males) ranged in age from 2 to 24 years, with a mean of 11 years. The data were divided into two groups: myopes, with a spherical equivalent refractive error ranging from −9.0 to −0.5 dioptres (mean, −2.50 dioptres), and non-myopes, with a spherical equivalent refractive error more positive than −0.5 dioptres (range, −0.38 to −4.38 dioptres; mean, −0.87 dioptres). Answers to questionnaires on nursery lighting conditions at night were collected from parents over the telephone, using the questions of Quinn et al. and a few extra ones. One asked parents to rate their confidence in the reliability of their recall of night-time lighting conditions from years earlier: 98% were confident in their responses.

The prevalence of myopia in our sample of children was not associated with ambient light exposure at night during their first two years, or later in life: 20% of those who slept with night lights before age 2 were myopic — the same incidence as in children who slept in the dark. There were no myopes among the small group who slept with full room illumination. This result was not related to either age of onset (mean, 10.5 years) or the severity of myopia.

Families with two myopic parents, however, reported the use of ambient lighting at night significantly more than those with zero or one myopic parent (χ2=7.42, P<0.025). This could be related either to their own poor visual acuity, necessitating lighting to see the child more easily at night, or to the higher socio-economic level of myopic parents, who use more child-monitoring devices. Myopia in children was associated with parental myopia, as reported previously2,3. The proportion of myopic children with two myopic parents was significantly greater than the proportion of myopic children with zero or one myopic parent (χ2=4.42, P<0.05).

Based on these results, we question whether parents need to be concerned about causing myopia in their children by lighting their nurseries at night.

See also K. Zadnik et al.  Reply: R. Stone et al.