Answer :
Final answer:
A child should progress to the next line on the Snellen chart once they can read at least half the letters on the current line during a visual acuity test.
Explanation:
When using the Snellen letter chart to assess a school-age child's visual acuity, the child should progress to the next line once they are able to read at least half the letters on the current line. This assessment is a commonly used method in optometry to gauge the clarity of a person's vision. Different lines on the Snellen chart correspond to certain vision standards, such as 20/20, 20/30, etc., where the top number refers to the distance in feet at which the test is taken, and the bottom number indicates the distance at which a person with normal vision could read the same line.
