Twenty-four hour ocular and systemic diurnal rhythms in children

Abstract

Purpose: Ocular diurnal rhythms have been implicated in myopia, glaucoma, diabetes, and other ocular pathologies. Ocular rhythms have been well described in adults; however, they have not yet been fully examined in children. The goal of this study was to investigate ocular and systemic diurnal rhythms over 24 h in children.

Methods: Subjects, ages 5 to 14 years (n = 18), wore a light, sleep, and activity monitor for one week to assess habitual sleep/wake patterns, then underwent diurnal measurements every 4 h for 24 h. Measurements included blood pressure, heart rate, body temperature, intraocular pressure (IOP), ocular biometry, and optical coherence tomography imaging. Saliva was collected for melatonin and cortisol analysis. Mean ocular perfusion pressure was calculated from IOP and blood pressure. Central corneal thickness, corneal power, anterior chamber depth, lens thickness, vitreous chamber depth, and axial length were determined from biometry. Total retinal thickness, retinal pigment epithelium (RPE) + photoreceptor outer segment thickness, photoreceptor inner segment thickness, and choroidal thickness were determined for a 1 mm diameter centred on the fovea. Subjects' amplitude and acrophase of diurnal variation for each parameter were determined using Fourier analysis, and mean acrophase was calculated using unit vector averaging.

Results: Repeated measures analysis of variance (ANOVA) showed that all parameters except anterior chamber depth exhibited significant variations over 24 h (p ≤ 0.005 for all). Axial length underwent diurnal variation of 45.25 ± 6.30 μm with an acrophase at 12.92 h, and choroidal thickness underwent diurnal variation of 26.25 ± 2.67 μm with an acrophase at 1.90 h. IOP was approximately in phase with axial length, with a diurnal variation of 4.19 ± 0.50 mmHg and acrophase at 11.37 h. Total retinal thickness underwent a significant diurnal variation of 4.09 ± 0.39 μm with an acrophase at 15.04 h. The RPE + outer segment layer was thickest at 3.25 h, while the inner segment layer was thickest at 14.95 h. Melatonin peaked during the dark period at 2.36 h, and cortisol peaked after light onset at 9.22 h.

Conclusions: Ocular and systemic diurnal rhythms were robust in children and similar to those previously reported in adult populations. Axial length and IOP were approximately in phase with each other, and in antiphase to choroidal thickness. These findings may have important implications in myopia development in children.

Keywords: axial length; choroidal thickness; circadian rhythms; cortisol; diurnal rhythms; melatonin.

Figure 1.

Protocol. Following screening and enrolment, subjects wore an Actiwatch for one week, then underwent ocular and systemic measurements every 4 h for 24 h. Grey areas represent the dark period.

Figure 2.

a) Representative infrared image showing the radial scan pattern and b) b-scan with segmentation as follows: inner limiting membrane (ILM, green), inner segment/outer segment border (ISOS, magenta), external limiting membrane (ELM, blue), retinal pigment epithelium/Bruch’s membrane junction (RPE-BM, red), and posterior choroid (yellow).

Figure 3.

Mean (± standard error) 24 h change in total retinal thickness (μm, black), retinal pigment epithelium + outer segment thickness (RPE+OS μm, red), and inner segment thickness (IS μm, green) for all subjects (n = 18); solid lines are cosinor fits to the data; grey areas represent the dark period.

Figure 4.

Mean (± standard error) 24 h change in axial length (μm, black), choroidal thickness (μm, red), intraocular pressure (IOP mmHg, green), and mean ocular perfusion pressure (MOPP mmHg, blue) for all subjects (n = 18); solid lines are cosinor fits to the data; grey areas represent the dark period.

Figure 5.

Mean (± standard error) change in melatonin concentration (filled symbols) and cortisol concentration (open symbols) across 24 h for all subjects (melatonin n = 16, cortisol n = 17); grey areas represent the dark period.