The leading cause of preventable blindness in children is vitamin A deficiency, estimated to cause 250,000-500,000 cases of childhood blindness annually. Vitamin A deficiency usually results from measles. A cataract is also one of the most common causes of blindness in children, affecting 20% of children with blindness. If left untreated, congenital cataracts (present at birth) can lead to amblyopia (lazy eye), which can cause permanent damage to vision. Pediatric cataracts affect older children and may be caused by trauma to the eye. In addition, infants can become blind from an eye infection, blocked tear ducts, strabismus, ptosis, congenital glaucoma, visual inattention, delayed development of the visual system, and retinopathy of prematurity.