by Scott Silverman, MD
Fellowship trained Pediatric Ophthalmologist

There has been tremendous public interest in a recent study from The Chidren's Hospital of Philadelphia which may link nearsightedness in children to nightlights. Dr. Graham Quinn published a study entitled "Myopia and ambient lighting at night" in the May 1999 issue of the scientific journal, Nature. This study has generated a flood of national media attention. Many parents have asked me about this study and whether or not they should turn off the nightlights in their baby's room.

What is myopia?
Nearsightedness is the common term for myopia. A myopic eye can see clearly up close but not in the distance. Myopia is usually first detected in elementary school when a child holds books very close or cannot read the chalkboard. In myopia, distant images are focused in front of the retina. Glasses, contacts, or refractive surgery can be used to restore clear vison. Those with myopia have a higher risk of retinal detachment and retinal degeneration.

Who gets myopia?
Myopia has a strong genetic link. When mom and dad are both nearsighted, their children almost always become nearsighted. Myopia is much less common when parents are not nearsighted. The prevalence of myopia varies between ethnic groups, with asians having the highest prevalence. Also, children from families of higher socio-economic status have a greater prevalence of myopia. There are differing theories to explain this link. One theory proposes that before the advent of glasses, those with myopia preferred reading and study to outdoor activity which translated to financial success which passed on through the generations.

The Study
Dr. Quinn explored the relationship between lighting at night and the prevalence of nearsightness. A retrospective questionnaire type study was conducted. Parents of 479 children completed a questionnaire and were asked "Under which lighting condition did your child sleep at night before the age of two?: (A) darkness; (B) nighlight; or (C) room light."

The differences between these groups were highly statistically significant (p<.00001). These results are quite dramatic. However, they do not prove a causal relationship between night lighting and nearsightedness, only an association. For example, this study did not attempt to factor out the effect of genetics or socio-economic status. As previously mentioned, children of higher socio-economic status are known to have a higher rate of nearsightedness. Perhaps a higher use of night lighting in this group explains the association rather than a true cause and effect between night lighting and nearsightedness. Only further investigation will fully answer the questions. It important to mention that this study found no effect of night lights in children over two years of age.

What does it mean?
Although this study does not establish a casual link, the statistical strength of the association of night lighting and nearsightedness is remarkable. In my opinion, it is reasonable to restrict night time lighting in children under two years of age. I will certainly keep the readers updated when further studies are released.