Final answer:
In a Romberg's test, the nurse should observe the client's ability to maintain balance with closed eyes, indicating the assessment of balance and proprioception.
Step-by-step explanation:
The nurse should evaluate the client's balance with eyes closed when performing a Romberg's test during the physical assessment. The Romberg test is an assessment tool specifically designed to test balance and proprioception, which are critical for maintaining an upright stance without visual input. During this test, the patient stands with feet together and closes their eyes. A loss of balance during the test suggests deficits in proprioceptive function or issues associated with the vestibular system.