الفهرس 
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Abstract
Vision is critical for daily activities, and visual impairment is one of the most serious disabilities. Visual impairment at birth or during childhood can affect learning, communication, employment, health, and quality of life, and the effects are often life-long.
Although the proportion of infants and school-aged children with visual impairment is less than 5%, children with visual impairment account for 20% of individuals with visual impairment worldwide, after adjustment for disability-adjusted life years (DALYs). The control of visual impairment and blindness in children is a priority of the World Health Organization’s VISION 2020 program.
Uncorrected refractive error is one of the most common causes of visual impairment in children. Increasing evidence indicates that uncorrected refractive error is a main cause of avoidable blindness in many regions.Refractive error and visual impairment have been surveyed during the past decade, and the findings confirm that refractive error is a predominant cause of visual impairment. However, further studies are required to explain these findings, due to differences in methodology, population characteristics, living environment, socioeconomic development, availability of primary health care, and ethnicity.
The most frequent ocular diseases are conjunctival and scleral disorder in all age groups except the eldest age group, followed by refractive error. However, an increasing number of people are at risk of visual impairment as populations grow and people live longer. Developing countries are already aging much faster than those in the developed world.