April 30, 2001
Night-lights no cause of myopia, study concludes
By Poul Olson
Constant light does not cause nearsightedness in infants, according to vision scientists at Yerkes and the College of Optometry at the University of Houston, who report recent findings in the May edition of Investigative Ophthalmology and Visual Science.
Co-authored by Yerkes Dolores Bradley and Houstons Earl Smith, the study challenges the conclusions of a 1999 investigation that found infants who sleep with night-lights or overhead lights left on are five times more likely to develop myopia than those who sleep in the dark.
In their study, Bradley and Smith examined nine infant rhesus monkeys,
between one and four weeks of age, that were reared in around-the-clock
room light for six months. The researchers compared these monkeys to 23
other infant monkeys reared with balanced periods of light and dark. The
monkey life stage examined in this study closely corresponds to the first
two years of human life, during which the human eye undergoes its most
intense developmental period.
The scientists tested the infants eyes for evidence of myopia using
retinoscopy, keratometry and A-scan ultrasonography. They found no significant
differences in corneal radius, refractive error or axial dimensions of
individual ocular components between the eyes of the monkeys exposed to
constant light and those of the controls.
Parents should not worry, Bradley said. Having lights
on at night does not cause myopia.
Whats well-established is that myopic parents tend to have
myopic children, Bradley said. By the same token, theres
a high correlation between nearsighted parents and those who turn on night-lights.
Myopic parents prefer to have night-lights on and are more likely to have
In addition to genetics, environment likely plays a role in the development
of myopia. Visual experience, especially early in life, is a factor
in both normal and abnormal refractive development, said Bradley.
Bradley and Smith believe the night-light study reaffirms the strength
of the rhesus model for studying myopia. Tradition-ally, researchers have
used chickens to model nearsightedness because of their relatively low
cost and the rapidity of their eyes development.
The model is limited, however, by the fact that chickens lack the binocular
visual system characteristic of the human visual system.
Chickens provide a means for evaluating and refining basic hypotheses,
but their eyes respond very differently to the stimuli affecting eye development,
Bradley said. Rhesus monkeys are ideal models for studying myopia
because their eyes develop in much the same way as those in people.
Currently, Yerkes and Houstons College of Optometry are the only
institutions in the world that use Old World monkeys (like the rhesus
macaque) to model eye development.
Bradley and Smith co-authored the study with Yerkes investigators Alcides
Fernandes and Ronald Boothe and Houstons Li-Fang Hung. Investigative
Ophthalmology and Visual Science is published by the Association for
Research in Vision and Ophthalmology, the international association for
clinical vision scientists.