Twenty-four hour ocular and systemic diurnal rhythms in children.
Level 4 - case-series / case-control
Single-arm observational physiological study (case-series design)
PubMed 31332822 · doi:10.1111/opo.12633
What was done
Eighteen children aged 5 to 14 years wore a light, sleep, and activity monitor for one week to track habitual sleep/wake patterns, followed by 24-hour measurements taken every 4 hours. Assessments included blood pressure, heart rate, body temperature, intraocular pressure (IOP), ocular biometry (corneal thickness and power, anterior chamber depth, lens thickness, vitreous chamber depth, and axial length), optical coherence tomography imaging (foveal retinal layer thicknesses and choroidal thickness), and salivary melatonin and cortisol. Diurnal variation amplitudes and acrophases were determined using Fourier analysis and repeated measures ANOVA.
What was found
All measured parameters except anterior chamber depth exhibited statistically significant 24-hour diurnal variation (p ≤ 0.005 for all): - Axial length varied by 45.25 ± 6.30 µm, peaking at 12.92 h. - Choroidal thickness varied by 26.25 ± 2.67 µm, peaking at 1.90 h. - IOP varied by 4.19 ± 0.50 mmHg, peaking at 11.37 h (approximately in phase with axial length). - Total retinal thickness varied by 4.09 ± 0.39 µm, peaking at 15.04 h (RPE + outer segment peaked at 3.25 h; inner segment peaked at 14.95 h). - Melatonin peaked in the dark period at 2.36 h, and cortisol peaked after light onset at 9.22 h.
Why it matters
This study provides baseline evidence that ocular and systemic circadian rhythms are robust in children and follow patterns similar to adults. These rhythms, particularly antiphase fluctuations between axial length and choroidal thickness, are relevant for pediatric myopia research and timing clinical measurements.
Limits
The study is limited by a small sample size (n = 18) across a wide developmental age range (5 to 14 years) monitored over only a single 24-hour laboratory cycle. The abstract does not report stratification by refractive error (e.g., emmetropic vs. myopic eyes) or longitudinal outcomes related to myopia onset.
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