Eye Length Fluctuates During the Day in Humans

Abstract

Abstract: : Purpose: Diurnal rhythms of eye length and choroidal thickness have been observed in juvenile and adult chickens and in marmosets. These fluctuations may relate to eye growth regulation. This study sought analogous intraday variation in eye length in children and adults. Methods: Participants underwent repeated axial length measurements using partial coherence interferometry (PCI) at various intervals from 7am to 1 am. PCI is a non-contact method that employs a short coherence superluminescence diode to create interference patterns between reflections from retinal surfaces and the corneal surface, with a 95% confidence interval for one measurement series of +16 µm. Three to five series of 16 measurements each were taken and an average axial length, defined as the distance from the anterior corneal surface to RPE/Bruch’s membrane, was calculated for each series (Francis, EL, ARVO Abstract #358, 2002). Results: Seventeen volunteer subjects participated, ages 7-53 yr (median 16 yr), mean spherical equivalent refractive error –0.68 (range –3.00 to +1.00). Individual axial length measurements as a function of time of day were modeled by sine functions, with the period restricted to 24 ± 6 hours. These models provided significantly good fits to the data (R²>0.67, p<0.05) for 9 of 17 subjects. For these 9 subjects, the magnitude of the intraday fluctuation (peak to trough) varied from 19.4 to 36.8 microns. Repeat measurements on a different day were obtained in 10 subjects. For six subjects, axial length showed intraday fluctuations on at least one of the two days. For four, sine fitting did not provide evidence for an intraday fluctuation on either measurement day. Conclusions: This study is the first demonstration in humans of intraday fluctuations in axial length. It represents another extension to humans of findings from animal studies of eye growth. Understanding these axial length fluctuations in humans is the subject of further work.

Keywords: circadian rhythms • refractive error development • emmetropization