C: Periorbital Cellulitis
Periorbital and orbital cellulitis, both of which are more common in children, have several overlapping features. The main differentiating factor is the absence of orbital signs (pain on movement, visual disturbance, proptosis) in periorbital cellulitis. This is due to the differing location of the infection. Periorbital cellulitis is an infection of tissues anterior to the orbital seprum (eyelids, skin, subcutaneous tissue, but NOT the contents of the orbit), whilst orbital cellulitis is an infection of the tissues posterior to the orbital septum (extra-ocular muscles, fat, but NOT the globe itself).
Keratoconjunctivitis sicca (dry eyes) & viral conjunctivitis classically present as a gritty, painful sensation in the eye with conjunctival redness.
Thyroid eye disease does not typically present acutely. Moreover, it classically presents with lid retraction, lid lag, exophthalmos and ophthalmoplegia.