Final answer:
The finding that requires intervention when visualizing a patient's tympanic membrane is when the left ear membrane appears oval in shape, which suggests a possible perforation or infection.
Step-by-step explanation:
When visualizing a patient's tympanic membrane with an otoscope, the nurse should be looking for any abnormalities that may require intervention. In this case, the finding that requires intervention is when the left ear membrane appears oval in shape. The normal tympanic membrane should be transparent, pearly white or pink in color, and have a round shape. The oval shape suggests a possible perforation or infection that should be evaluated further by a healthcare professional.