D L Nickla1, C F Wildsoet, D Troilo. 1. New England College of Optometry, 424 Beacon Street, Boston, MA 02115, USA. nicklad@ne-optometry.edu
Abstract
PURPOSE: To determine whether the diurnal rhythms in axial length and choroidal thickness in the chick eye are endogenous circadian rhythms. METHODS: Six chickens, 14 days of age, were put into darkness for 4 days. Beginning on the 3rd day, ocular dimensions were measured using high-frequency A-scan ultrasonography, in darkness, at 6-hour intervals over 48 hours. Five age-matched chickens reared in a normal light/dark (L/D) cycle and measured at 6-hour intervals for 5 days were controls. RESULTS: The rhythms in axial length and choroidal thickness persist in constant darkness. The phases of these rhythms are approximately in antiphase to one another, similar to those of eyes in a L/D cycle; however, the peak of the rhythm in axial length occurs slightly earlier relative to that of eyes in L/D (12 PM versus 3 PM; P: < 0.05, one-tailed t-test). By the 3rd day in darkness, the rate of growth is significantly higher than that in L/D (117 versus 72 microm/24 hours; P: < 0.01), and the choroid becomes significantly thinner (159 versus 210 microm; P: < 0.0001). CONCLUSIONS: The rhythms in axial length and choroid thickness are circadian rhythms, driven by an endogenous oscillator. The phase of the rhythm in axial length in constant darkness is slightly phase-advanced relative to eyes in L/D and thus is similar to eyes that are deprived of form vision. These findings suggest that in the absence of visual input, the eyes revert to a "default" growth state and that the similarities between the effects of constant darkness and of form deprivation suggest that deprivation may represent a type of "constant" condition.
PURPOSE: To determine whether the diurnal rhythms in axial length and choroidal thickness in the chick eye are endogenous circadian rhythms. METHODS: Six chickens, 14 days of age, were put into darkness for 4 days. Beginning on the 3rd day, ocular dimensions were measured using high-frequency A-scan ultrasonography, in darkness, at 6-hour intervals over 48 hours. Five age-matched chickens reared in a normal light/dark (L/D) cycle and measured at 6-hour intervals for 5 days were controls. RESULTS: The rhythms in axial length and choroidal thickness persist in constant darkness. The phases of these rhythms are approximately in antiphase to one another, similar to those of eyes in a L/D cycle; however, the peak of the rhythm in axial length occurs slightly earlier relative to that of eyes in L/D (12 PM versus 3 PM; P: < 0.05, one-tailed t-test). By the 3rd day in darkness, the rate of growth is significantly higher than that in L/D (117 versus 72 microm/24 hours; P: < 0.01), and the choroid becomes significantly thinner (159 versus 210 microm; P: < 0.0001). CONCLUSIONS: The rhythms in axial length and choroid thickness are circadian rhythms, driven by an endogenous oscillator. The phase of the rhythm in axial length in constant darkness is slightly phase-advanced relative to eyes in L/D and thus is similar to eyes that are deprived of form vision. These findings suggest that in the absence of visual input, the eyes revert to a "default" growth state and that the similarities between the effects of constant darkness and of form deprivation suggest that deprivation may represent a type of "constant" condition.
Authors: David Troilo; Earl L Smith; Debora L Nickla; Regan Ashby; Andrei V Tkatchenko; Lisa A Ostrin; Timothy J Gawne; Machelle T Pardue; Jody A Summers; Chea-Su Kee; Falk Schroedl; Siegfried Wahl; Lyndon Jones Journal: Invest Ophthalmol Vis Sci Date: 2019-02-28 Impact factor: 4.799