You might tell your patients to have their grandchildren sleep in dark rooms.

Researchers at the University of Pennsylvania Medical School in Philadelphia studied 479 children aged 2 to 16 who attended an eye clinic. They asked the children whether they slept in the dark, with a nightlight on, or with a room light on.

Ten percent of those who slept in the dark developed myopia, compared to 34% who used a nightlight and 55% of those who slept with the room light on.

The researchers believe a nightly period of full darkness in early childhood, especially during the first 2 years, may be essential to proper eye development. However, they caution that others factors probably also contribute to development of myopia and believe more studies are needed.