Sympathetic nervous system activity is associated with choroidal thickness and axial length in school-aged children

We aim to explore the effect of sympathetic nervous system (SNS) on choroid thickness (ChT) and axial length (AL).

Students of grade 2 and 3 from a primary school were included and followed for 1 year. Visual acuity, refraction, AL and ChT were measured. Morning urine samples were collected for determining SNS activity by analysing concentrations of epinephrine, norepinephrine and dopamine using the liquid chromatography-tandem mass spectrometry. The most important factor (factor 1) was calculated using factor analysis to comprehensively indicate the SNS activity.

A total of 273 students were included, with an average age of 7.77±0.69 years, and 150 (54.95%) were boys. Every 1 µg/L increase in epinephrine is associated with 1.60 µm (95% CI 0.30 to 2.90, p=0.02) decrease in average ChT. Every 1 µg/L increase in norepinephrine is associated with 0.53 µm (95% CI 0.08 to 0.98, p=0.02) decrease in the ChT in inner-superior region. The factor 1 was negatively correlated with the ChT in the superior regions. Every 1 µg/L increase in norepinephrine was associated with 0.002 mm (95% CI 0.0004 to 0.004, p=0.016) quicker AL elongation. The factor 1 was positively correlated with AL elongation (coefficient=0.037, 95% CI 0.005 to 0.070, p=0.023).

We hypothesised that chronic stress characterised by elevated level of the SNS, was associated with significant increase in AL elongation, probably through thinning of the choroid.