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Earl L. Smith, Dolores V. Bradley, Alcides Fernandes, Li-Fang Hung, Ronald G. Boothe; Continuous Ambient Lighting and Eye Growth in Primates. Invest. Ophthalmol. Vis. Sci. 2001;42(6):1146-1152.
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purpose. To determine the effect of continuous light exposure on ocular growth
and emmetropization in infant monkeys.
methods. Nine infant rhesus monkeys were reared with the normal vivarium
lights on continuously. The 24-hour light cycle was initiated between 1
and 4 weeks of age and maintained for 6 months. The ocular effects of
continuous light were assessed by cycloplegic retinoscopy, keratometry,
and A-scan ultrasonography. Longitudinal control data were obtained
from 23 normal infants that were reared with an illumination cycle that
included defined light and dark phases (either 12-hour light:12-hour
dark or 8.5-hour light:15.5 hour dark).
results. In contrast to previous studies involving light-reared chickens, no
monkeys exhibited exaggerated ocular growth. There were no significant
differences between treated and control monkeys in corneal radius,
overall eye size, or the axial dimensions of individual ocular
components. At the end of the treatment period, eight of the nine
experimental monkeys also exhibited the moderate hyperopic errors
(range, +1.5 to +3.4 D) that are typically found in normal animals.
Aspects of emmetropization were, however, unusual for three monkeys.
One monkey manifested a −0.50 D myopic error that was associated with
an abnormally steep cornea but had normal axial lengths. Two additional
monkeys developed persistent axial anisometropias.
conclusions. In infant primates constant light exposure does not promote the
constellation of ocular changes (in particular corneal flattening, a
decrease in anterior chamber depth, and an increase in vitreous chamber
depth) that has been observed in light-reared chickens. The slight
variations from the expected developmental sequence observed in three
infants may reflect individual differences. However, it is also
possible that aspects of the emmetropization process may not operate as
effectively under constant light as they do under an ordinary
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