Since children's eyes develop so rapidly, and they continue to develop until about the age of seven, early detection is essential to correcting potentially permanent vision issues. Furthermore, a standard in-school screening only tests for visual acuity which does not provide the whole picture. Comprehensive eye exams test for visual acuity, color vision, eye alignment, eye health and other chronic diseases such as diabetes.If a child waits too long to have an eye exam, a correctable visual problem may become permanent. For example, while a crossed eye may not seem bad, if left untreated, it can cause serious damage. When one eye isn't functioning properly, the brain often begins to ignore it. Once that starts to happen, it renders that eye essentially blind. However, if a child is treated early, a lazy eye can be fixed fairly simply and any permanent damage can be avoided.