Final answer:
The distinguishing clinical finding between periorbital and orbital cellulitis is worsening pain with eye movements, which indicates the infection has spread to the muscles controlling eye movement.
Step-by-step explanation:
The question is asking about differentiating clinical findings between periorbital and orbital cellulitis. The correct answer to this question is worsening pain with eye movements. Both periorbital (also known as preseptal) cellulitis and orbital cellulitis may present with erythema (redness), fever, and lid edema. However, orbital cellulitis is characterized by infection that has spread to the eye socket, which often results in pain that worsens with eye movement due to the inflammation and infection affecting the muscles that control eye movement. This symptom is not typically present with periorbital cellulitis. Therefore, worsening pain with eye movements is a distinguishing clinical finding for orbital cellulitis.