This patient has orbital cellulitis, which is inflammation of the structures of the orbit, including the extraocular muscles and orbital fat. Orbital cellulitis often results from a contiguous dental or sinus infection, as was likely present in this patient. Clinical characteristics of orbital cellulitis include eyelid swelling, ophthalmoplegia, pain with eye movement, and occasionally proptosis. Because it is a deep infection and involves critical structures, rapid diagnosis and treatment are necessary to preserve vision and prevent extension to central nervous system structures. CT is used to evaluate the extent of infection and to exclude abscess, which may need surgical drainage. This patient requires hospitalization and intravenous antibiotics.

Blepharitis is inflammation of the sebaceous glands or lash follicles of the eyelid, which can progress to conjunctivitis or keratitis. It usually presents with findings limited to the eyelid, although patients may complain of a gritty, burning sensation in the eye. Blepharitis is not associated with the key findings of orbital cellulitis.

Endophthalmitis is inflammation of the aqueous and vitreous humors. Symptoms may include visual loss, photophobia, and ocular pain and discharge. It is usually caused by bacterial or fungal infection following surgery, especially for cataracts. Other causes are globe trauma and foreign bodies.

Preseptal cellulitis is inflammation that is limited to the areas of the eyelids and facial tissues that are anterior to the orbital septum. It is more common than orbital cellulitis in adults and can usually be differentiated from orbital cellulitis by pain localized to the anterior tissues without ophthalmoplegia, pain with eye movement, or proptosis, which this patient has. Therefore, it is a less likely diagnosis in this patient.