Abstract
Purpose: :
Recent data suggest that outdoor activity is protective against myopia prevalence, but not progression, in children. This effect may be mediated by several possible pathways, including upregulation of levels of vitamin D3. We examined whether oral vitamin D3 supplement affects the onset or time-course of minus lens compensation or form deprivation myopia in tree shrews.
Methods: :
Juvenile tree shrews (weight ~ 125g) were fed 300 IU of vitamin D3 (cholecalciferol) in applesauce per day (~200X the recommended human daily dosage by weight). Consumption of the treated applesauce was monitored to verify the daily dosage. A group of 15 animals that were not fed vitamin D3 provided control data on normal vitamin D3 levels. Animals were pre-treated with vitamin D3 for 7 days and then continued receiving vitamin D3 during 13 days of monocular -5D lens treatment (n=5) or 13 days of monocular form deprivation (MD) (n=5). Non-cycloplegic refractive measures were made daily in awake animals (Nidek autorefractor). At the end of treatment, ocular component dimensions were measured with a-scan ultrasound, blood was drawn, and serum levels of 25-hydroxyvitamin D {25(OH)D} were measured. The refractive and ocular changes in the MD and -5D lens animals were compared to animals from previous studies that were not fed vitamin D3.
Results: :
The average 25(OH)D level in animals not treated with vitamin D3 was 30.2 ± 13.2 ng/ml. The levels in animals fed vitamin D3 were >142 to >1512 ng/ml (average > 1169 ng/ml). During the pre-treatment period, the eyes followed a normal emmetropization pattern which continued for the control eyes after treatment began. The treated eyes of both groups developed myopia (-5.5 ± 0.2 D, -5 D lens; -7.5 ± 0.6 D, form deprivation) and vitreous chamber elongation (0.12 ± 0.01 mm, -5 D lens; 0.20 ± 0.01 mm, form deprived)( mean treated - control ± SEM). There were no significant differences in the onset, rate of myopia development, or amount of myopia between animals that were fed vitamin D3 and those that were not.
Conclusions: :
Oral vitamin D3 supplement that dramatically raises 25(OH)D blood serum levels does not affect myopia induced with either a minus lens or form deprivation in tree shrews. These data suggest that elevated vitamin D blood levels do not protect against visually induced myopia development.
Keywords: myopia • sclera • refractive error development