Effects of ultra violet radiation on serum vitamin D levels in chick experimental myopia models

Abstract

Purpose : It has been reported that sun exposure may suppress progression of myopia in previous studies. The mechanism of myopia progression modulated by light exposure has, however, still been unclear. In this study, we investigated the effects of short wavelength ultra violet (UV) exposure on the initiation and progression of myopia analyzing chick lens-induced myopia (LIM) models.

Methods : One eye of each chick was covered by a minus 9 diopter glass goggle to produce an LIM model from postnatal day 5 to 12 for 7 days. The animals were randomly assigned to two groups, one of which is put under a white visible light environment, the control group, and the other is under the environment of 305-nm UV exposures, the UV exposure group. The control group had 18 chicks, and the UV group had 21. The animals were kept under a 12/12-hour light-dark cycle. Ocular components including axial length were evaluated by a B-mode ultrasound. Serum 25-OH vitamin D level and body weight changes were also analyzed. Statistics were performed using a Student t-test and a Spearman’s rank sum correlation test. The p value was considered significant when it is less than 0.05.

Results : The UV exposure group showed a significant (p=0.017) shorter axial length (8.28±0.33 mm, mean±SD) and a significant (p<0.001) shorter vitreous chamber depth (5.69±0.22 mm) compared to the control group in LIM eyes (8.52±0.26 mm and 6.02±0.22 mm, respectively). A significant (p<0.001) increase of the serum 25-OH vitamin D level (90.38±24.56 ng/ml) and a significant (p<0.001) decrease of the body weight changes (30.89±5.56 grams) were observed by the UV exposure compared to the control group (39.56±12.06 ng/ml and 54.29±4.27 grams, respectively). The vitamin D levels were inversely correlated with the axial length in uncovered eyes (y=-0.048x+1.4263, R²=0.1568, p=0.014), whereas they were not in LIM eyes. Some chicks were found to have ulcerative lesions on the feet and corneae.

Conclusions : Short wavelength UV, 305-nm, irradiation induced various ocular and systemic parameter changes. Serum vitamin D level may be associated with myopia initiation, but not with its progression. Short wavelength UV irradiation may be detrimental causing skin and corneal ulcers.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.