Objective: Due to the northern location of Denmark, the length of the day over the year varies from 7 to 17.5 hours. Experimental and clinical results suggest that the development of myopia may be related to ambient light exposure. The purpose of current study was to investigate whether axial eye growth, myopia progression, or corneal curvature change in Danish myopic children varies with exposure to daylight.
Methods: Two hundred thirty-five children aged 8-14 years found to have myopia in a screening procedure for a clinical trial (ClinicalTrial.gov NCT00263471). All children found to have a cycloplegic myopia of -0.063 or more at the first of two visits were included. Cycloplegic refraction was measured using an autorefractor, axial eye length and corneal curvature using an automatic combined non-contact partial coherence interferometer and keratometer. Accumulated exposure to daylight during the measurement period was calculated for each participant using an astronomical table.
Results: Accumulated daylight exposure ranged from 1660 to 2804 hours. Significant correlations were found between daylight exposure and eye elongation (p=0.000) myopia progression (p=0.014), and corneal curvature change (p=0.000). In children exposed to an average of 2781.64 +/- 18.63 hours of daylight, axial eye growth was 0.117 +/-0.088 mm, myopia progression 0.256 +/- 0.267 diopters, and corneal curvature change 0.048 +/- 0.102 diopters, whereas in children exposed to an average of 1681.49 +/- 24.49 hours of daylight, axial eye growth was 0.186 +/-0.097 mm, myopia progression 0.319 +/- 0.267 diopters, and corneal curvature change -0.035 +/- 0.084 diopters.
Conclusions: Eye elongation appears to increase in periods with shorter days. The cornea tends to flatten in periods with shorter days and steepen in periods with longer days. Myopia progression decreases during periods with longer days. Use of indoor light sources imitating daylight may be considered as a means of retarding myopia progression. Medical treatment directed at reducing myopia progression may be particularly effective if administered during the hours with least daylight.