Elevated Melatonin Levels Found in Young Myopic Adults Are Not Attributable to a Shift in Circadian Phase

Abstract

To evaluate the relationship between refractive error, circadian phase, and melatonin with consideration of prior light exposure, physical activity, and sleep. METHODS. Healthy young myopic (spherical equivalent refraction [SER] ≤−0.50DS) and emmetropic adults underwent noncycloplegic autorefraction and axial length (AL) measures. Objective measurements of light exposure, physical activity, and sleep were captured across 7 days by wrist-worn Actiwatch-2 devices. Questionnaires assessed sleep quality and chronotype. Hourly evening saliva sampling during a dim-light melatonin onset (DLMO) protocol evaluated circadian phase, and both morning serum and saliva samples were collected. Liquid chromatography/mass spectrometry quantified melatonin. RESULTS. Subjects (n = 51) were aged 21.4 (interquartile range, 20.1−24.0) years. Melatonin was significantly higher in the myopic group at every evening time point and with both morning serum and saliva sampling (P ≤ 0.001 for all). DLMO-derived circadian phase did not differ between groups (P = 0.98). Multiple linear regression analysis demonstrated significant associations between serum melatonin and SER (B =-.34, β =-.42, P = 0.001), moderate activity (B = .009, β = .32, P = 0.01), and mesopic illumination (B =-.007, β =-.29, P = 0.02), F(3, 46) = 7.23, P < 0.001, R 2 = 0.32, R 2 adjusted = .28. Myopes spent significantly more time exposed to "indoor" photopic illumination (3 to ≤1000 lux; P = 0.05), but "indoor" photopic illumination was not associated with SER, AL, or melatonin, and neither sleep, physical activity, nor any other light exposure metric differed significantly between groups (P > 0.05 for all). CONCLUSIONS. While circadian phase is aligned in adult myopes and emmetropes, myopia is associated with both elevated serum and salivary melatonin levels. Prospective studies are required to ascertain whether elevated melatonin levels occur before, during, or after myopia development.

Influence of Circadian Rhythm in the Eye: Significance of Melatonin in Glaucoma

“…It should be considered that dopamine and melatonin circadian cycles oscillate in antiphase in the central nervous system [140], including the retina [141]. In this sense, recent studies showed that melatonin levels in body fluids such as serum and saliva were elevated in myopic subjects compared to emmetropes ones [142,143], but they were reduced in urine [144]. In accordance with the above, dopamine levels were also reduced in the serum of these myopic subjects [142].…”

IMI Risk Factors for Myopia

“… 263 More recently, this group reported that circadian rhythms in melatonin levels were not altered in myopes as compared with emmetropes. 265 In contrast, a more recent paper reported that melatonin levels were lower, and that there were phase shifts in rhythms. 266 At this stage, it is not clear whether these observations suggest a role for circadian rhythms, or whether the changes in melatonin levels are secondary to changes in dopamine metabolism.…”

Measuring morning melatonin levels with plasma melatonin ELISA kits is a poor choice on two levels

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