Significantly higher serum melatonin in human myopes

(HealthDay)—Human myopes exhibit significantly higher serum melatonin (Mel) concentration than non-myopes, according to a study published online July 18 in Ophthalmic & Physiological Optics.

Stephanie Kearney, from the University of Ulster in Coleraine, U.K., and colleagues examined the correlation between myopia and serum concentrations of dopamine (DA) and Mel in 54 participants (aged 19.1 ± 0.81 years); nine participants were lost to follow-up. Solid phase extraction-liquid chromatography-tandem mass spectrometry was used to measure morning serum concentrations of DA and Mel in September/October 2014 (phase 1) and March/April 2016 (phase 2). The authors also recorded axial length (AL), corneal radii (CR), and spherical equivalent refraction (SER).

The researchers found that at phases 1 and 2, myopes exhibited significantly higher Mel concentrations than non-myopes (median differences, 10 and 7.3 pg mL⁻¹, respectively; both P < 0.001); at phase 2, DA concentrations were also lower in myopes (median difference, 4.7 pg mL⁻¹; P = 0.006). There was a positive association for Mel concentrations with more negative SER (all r ≥ − 0.53; all P < 0.001), longer AL (all r ≥ 0.37; all P ≤ 0.008), and higher AL/CR ratio (all r ≥ 0.51; all P < 0.001).

"This study reports for the first time in humans that myopes exhibit higher serum Mel concentrations than non-myopes," the authors write. "This may indicate a role for light exposure and circadian rhythm in the human myopic growth mechanism."