A 10-year-old girl presents with a 3-month history of mornin…

A 10-year-old girl presents with a 3-month history of morning stiffness lasting over an hour, swelling of the right knee and left wrist, and intermittent low-grade fevers. She also reports increased difficulty seeing the board at school. Labs show mild anemia, elevated ESR, negative RF, and positive ANA. Which next steps is most important in confirming the diagnosis and preventing complications?