Twenty-four hour ocular and systemic diurnal rhythms in children.

Abstract

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 24h in children. Subjects, ages 5 to 14years (n=18), wore a light, sleep, and activity monitor for one week to assess habitual sleep/wake patterns, then underwent diurnal measurements every 4h for 24h. 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 1mm 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. Repeated measures analysis of variance (ANOVA) showed that all parameters except anterior chamber depth exhibited significant variations over 24h (p≤0.005 for all). Axial length underwent diurnal variation of 45.25±6.30μm with an acrophase at 12.92h, and choroidal thickness underwent diurnal variation of 26.25±2.67μm with an acrophase at 1.90h. IOP was approximately in phase with axial length, with a diurnal variation of 4.19±0.50mmHg and acrophase at 11.37h. Total retinal thickness underwent a significant diurnal variation of 4.09±0.39μm with an acrophase at 15.04h. The RPE + outer segment layer was thickest at 3.25h, while the inner segment layer was thickest at 14.95h. Melatonin peaked during the dark period at 2.36h, and cortisol peaked after light onset at 9.22h. 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.