Inclusion Criteria:(Group 1):  age <18 years old serum vitamin D [(25(OH) D), calcitriol] level <20 ngr/mL in previous two weeks visual acuity >20/20 manifest refraction spherical equivalent <3D normal biomicroscopic and fundus examination.  Exclusion Criteria:  history of any chronic ocular diseases, except for refractive error (e.g., uveitis, glaucoma, retinopathy of prematurity) history of ocular surgery (e.g., cataract, strabismus, open globe injury, laser photocoagulation) having an ocular abnormality (e.g., persistent fetal vasculature, optic disc hypoplasia, fovea plana) history of systemic diseases that have the potential to affect ocular tissues (e.g., diabetes mellitus, Graves' disease, albinism, Down syndrome, Fabry diseases, Wilson syndrome) history of any systemic diseases that can affect the serum vitamin D level (e.g., parathormone or calcium metabolism disorders) already receiving vitamin D treatment.