Abstract
Experimental animal models of myopia demonstrate that higher melatonin (Mel) and lower dopamine (DA) concentrations actively promote axial elongation. This study explored the association between myopia and serum concentrations of DA and Mel in humans. Morning serum concentrations of DA and Mel were measured by solid phase extraction-liquid chromatography-tandem mass spectrometry from 54 participants (age 19.1 ± 0.81 years) in September/October 2014 (phase 1) and March/April 2016 (phase 2). Axial length (AL), corneal radii (CR) and spherical equivalent refraction (SER) were also recorded. Participants were defined as myopic if non-cycloplegic spherical equivalent refractive error ≤-0.50 DS at phase 1. Nine participants were lost to follow up. Mel concentrations were measurable for all myopes (phase 1 n = 25, phase 2 n = 22) and non-myopes (phase 1 n = 29, phase 2 n = 23). SER did not change significantly between phases (p = 0.51). DA concentrations were measurable for fewer myopes (phase 1 n = 13, phase 2 n = 12) and non-myopes (phase 1 n = 23, phase 2 n = 16). Myopes exhibited significantly higher Mel concentrations than non-myopes at phase 1 (Median difference: 10 pg mL-1 , p < 0.001) and at phase 2 (Median difference: 7.3 pg mL-1 , p < 0.001) and lower DA concentrations at phase 2 (Median difference: 4.7 pg mL-1 , p = 0.006). Mel concentrations were positively associated 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. This may indicate a role for light exposure and circadian rhythm in the human myopic growth mechanism. Further research should focus on younger cohorts exhibiting more dynamic myopic progression and explore the profile of these neurochemicals alongside evaluation of sleep patterns in myopic and non-myopic groups.
Highlights
Myopia presents an economic burden both in terms of the cost of refractive correction and the increased risk of visual impairment arising from associated pathology including glaucoma[1] and chorioretinal atrophy.[2,3] Myopia is a growing health concern[4] with global estimates indicating the number of cases of myopia will reach 324 million by 2025 resulting in an increase in the prevalence of pathological scleral and choroidal degenerations associated with high myopia.[3]
Spherical equivalent refraction was relatively stable over the study period in both the myopic and the non-myopic groups and change in spherical equivalent refraction (SER) was not statistically significant in either group
The association found between Mel and myopic refractive error is further supported by positive associations between Mel, Axial length (AL) and AL/corneal radii (CR); most strongly between Mel and AL to CR ratio (AL/CR)
Summary
Myopia presents an economic burden both in terms of the cost of refractive correction and the increased risk of visual impairment arising from associated pathology including glaucoma[1] and chorioretinal atrophy.[2,3] Myopia is a growing health concern[4] with global estimates indicating the number of cases of myopia will reach 324 million by 2025 resulting in an increase in the prevalence of pathological scleral and choroidal degenerations associated with high myopia.[3]. To-date the most promising interventions include modifying the image profile projected to the peripheral retina,[12,13] increasing the amount of time a child spends outdoors,[7,14,15] and application of pharmacological agents such as adenosine antagonist 7-methylxanthine (7-mx)[16] or the anti-cholinergic agent atropine[8] The latter has recently been shown to cause thickening of the choroid in young children (aged 5– 10 years).[17] The mechanism by which these visual, environmental and pharmacological interventions influence refractive status are currently unclear. Chicks in which systemic administration of Mel promoted choroidal thinning[32] and in guinea pigs where the systemic injection of a precursor of DA (levodopa) retarded the development of form deprivation myopia.[52] Ocular Mel and systemic circulating Mel concentrations have been shown to be associated in the frog[53] and Newt eye.[54]. The aim of this prospective, observational study was to explore the association between myopia and serum concentrations of DA and Mel in a human population for the first time
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
