Final answer:
The nurse should instruct the child to cover the left eye when beginning the Snellen chart test and then test the right eye to measure visual acuity.
Step-by-step explanation:
When using the Snellen chart to assess a school-age child's visual acuity, the nurse should instruct the child to cover the left eye first, then move to the right eye. This standardized test is used to measure how well the child can see the details of letters from a specific distance, typically 20 feet. It presents a limited number of Roman letters in lines of decreasing size. The specific line that a person can comfortably read without squinting gives an estimate of their visual acuity, like the commonly referenced 20/20 vision.
Visual acuity testing is a routine part of an optometry evaluation and is critical in identifying issues with sight, such as myopia (nearsightedness), which commonly presents in school-aged children. Individuals with a family history of glasses use or those who engage in significant amounts of close visual work may be more prone to develop vision problems.