Purpose: 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. Methods: Morning serum concentrations of DA and Mel were measured by solid phase extraction-liquid chromatography-tandem mass spectrometry from 54 participants (age 19.1 AE 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 ≤À0.50 DS at phase 1. Results: 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 À1 , p < 0.001) and at phase 2 (Median difference: 7.3 pg mL À1 , p < 0.001) and lower DA concentrations at phase 2 (Median difference: 4.7 pg mL À1 , p = 0.006). Mel concentrations were positively associated with more negative SER (all r ≥ À0.53, 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).Conclusion: 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.

Myopia was associated with smaller areas of CUVAF indicative of less cumulative ultraviolet-B exposure. These findings suggest that CUVAF measures are a useful, non-invasive biomarker of the time spent outdoors in adults in northern hemisphere populations.

CUVAF area and intensity were not associated with clinical measures of dry eye. Greater CUVAF area and intensity were associated with wearing sunglasses less frequently and spending more time outdoors. If sunglass wear is accounted for, CUVAF may be a useful biomarker of time spent outdoors in future myopia studies.

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Purpose: Near work, accommodative inaccuracy and ambient lighting conditions have all been implicated in driving the myopic development mechanism. However, difference in accommodative responses with age and refractive error under different visual conditions remain unclear. This study explores differences in accommodative abilities and refractive error when exposed to differing ambient illumination and visual demands in Malay schoolchildren and adults.Methods: Sixty young adults (21-25 years) and sixty school children (8-12 years) were recruited. Accommodative lag and accommodative fluctuations at far (6 m) and near (25 cm) were measured using the Grand Seiko WAM-5500 open field autorefractor. The effect of mesopic room illumination on accommodation were also investigated.Results: Repeated measures ANOVA indicated that accommodative lag at far and near was significantly different in school children and young adults (F(1.219, 35.354) = 11.857, p < 0.05) with post hoc tests using the Bonferroni correction determined that at near, there was a greater lag in school children (0.486 ± 0.181 D) than young adults (0.259 ± 0.209 D, p < 0.05). Repeated measures ANOVA also determined that accommodative lag differed statistically at near demands between non-myopic group and the myopic group in young adults and school children (F(3.107, 31.431) = 12.187, p < 0.05). Post hoc tests using the Bonferroni correction showed that accommodative lag at near was significantly greater in myopic school children (0.655D ± 0.198D) compared with non-myopic school children (0.202D ± 0.141D, p < 0.05) and myopic young adults (0.316D ± 0.172D, p < 0.05), but no significant difference between myopic young adults (0.316D ± 0.172D) and non-myopic young adults (0.242D ± 0.126D, p > 0.05). Accommodative lag and fluctuations were greater in mesopic room conditions for all ages [all p < 0.05]. Conclusion:Greater accommodative lag was found in myopes compared to emmetropes, school children compared to adults and in mesopic compared to photopic conditions. Accommodative fluctuations were greatest in myopes and in mesopic conditions. These results suggest that differences exist in the amount of blur experienced by myopes and non-myopes at different ages and in different lighting conditions.