Orbital infection may occur after orbital surgery. Infection may also occur after treatment of endophthalmitis due to direct inoculation of the orbit by the infected globe. Staph. aureus is again the most likely organism, but anaerobic and mixed infections can also occur. Orbital infection typically develops within the first 2–3 days after surgery, and clinical signs of orbital infection may initially be mistaken as orbital edema and erythema secondary to expected orbital congestion after surgery. Fever, discharge, and leukocytosis point more clearly to orbital infection rather than routine healing [2].

Sinusitis is the most common cause of orbital infection and is found in 70–90% of cases of orbital cellulitis [6]. Clinical features of sinusitis-related orbital infection include headache, rhinorrhea, fever, and eyelid swelling. Purulent discharge from the nose can also be seen. The orbital infection typically progresses rapidly with acute onset of eyelid edema , proptosis , and motility restriction (Fig. 2.2). Fever and leukocytosis are also often seen. Vision changes and double vision may develop due to orbital congestion but may not be discerned initially due to eyelid swelling and pain. Sinusitis-related orbital infection is most commonly caused by sinus pathogens such as Staph. aureus, Strep. pneumoniae, or other Streptococcus species and anaerobes [2]. The most frequently infected sinus is the ethmoid, followed by maxillary, frontal, and sphenoid. Often two or more sinuses are involved with the most common paired infections being that of the ethmoid and maxillary sinuses [7]. There is a suggestion of increased occurrence of orbital cellulitis during the winter months due to increased rates of sinusitis at this time [8].

Mucormycosis is a rare but serious fungal infection caused by a group of molds called mucormycetes . Classic predisposing risk factors for mucormycosis include diabetic ketoacidosis or immunosuppression related to chemotherapy, immunotherapy, chronic steroid treatment, prior radiation, or immune deficiency diseases [9]. Mucormycosis has also occurred in previously undiagnosed or mild diabetics. The clinical course is characterized by aggressive progression of illness. Initial symptoms may include headache, orbital pain, and fever. Within 1–7 days, typical signs of orbital congestion, including proptosis, restricted motility, and vision changes, may be accompanied by anesthesia or paresthesia of the ophthalmic and maxillary branches of the trigeminal nerve as well as of the facial nerves. Necrosis of orbital tissue and of the adjacent nasal and oral mucosa may occur resulting in a dark, gangrenous appearance to the tissues. Inflammation and perforation of the ipsilateral eardrum have also been reported. Physical exam should include evaluation of the nasal and oral mucosa, and an otolaryngology evaluation should be requested if mucormycosis is suspected [2].

Aspergillosis is a more indolent orbital infection which is characterized by slow progression of orbital inflation, occurring over the course of months to years [10].

Rarely, orbital cellulitis occurs as a result of other infections. The orbit may become infected due to endophthalmitis or panophthalmitis that has extended through the sclera (Fig. 2.3). Acute dacryocystitis with extension of infection from the nasolacrimal sac past the orbital septum can also result in orbital cellulitis [11]. These infections are typically due to Staph. aureus and Streptococcus species. Dental infections resulting in maxillary sinusitis can rarely cause orbital cellulitis and are typically due to mixed bacteria, including anaerobes. Osteomyelitis of the orbital bones and phlebitis of facial veins are other, rare, potential causes of orbital cellulitis [12]. A careful history, including inquiring about recent surgery, trauma, infections, and systemic symptoms, and a detailed physical exam, with special attention to the orbit and facial region, should be performed as part of the clinical evaluation of patients with suspected orbital cellulitis [2].

Physical examination findings are critical to making a prompt diagnosis of orbital cellulitis. Examination should begin with an assessment of vital signs and general medical condition. Patients with orbital cellulitis often show systemic signs of illness such as fever and may have fatigue and loss of appetite. In severe cases, patients may appear toxic. External examination of the face should include objective measurement of globe position. Both orbital and preseptal cellulitis can cause significant eyelid edema ; however, a finding of proptosis is strongly suggestive of orbital cellulitis. A focused eye exam can show decreased vision and decreased color vision due to optic neuritis or compressive optic neuropathy. A pupil exam should also be performed to observe for abnormalities related to orbital or optic nerve inflammation or mass effect due to orbital abscess. Extraocular motility deficits and pain with eye movement are also physical exam findings which are strongly supportive of a diagnosis of orbital cellulitis. The swollen lid should be lifted for careful examination of the globe as well (Fig. 2.4). Injection of the conjunctiva and conjunctival chemosis are signs which are consistent with orbital cellulitis. A complete eye exam should be performed including evaluation of the optic nerve for optic nerve head edema, which may suggest optic nerve inflammation or compression. Significant periorbital pain, pain with eye movement, and globe injection are earlier signs which point to orbital cellulitis before the onset of later findings such as proptosis, extraocular motility restriction, optic disc swelling, and decreased vision [13]. The spectrum of periorbital and orbital infection ranges from preseptal cellulitis to orbital cellulitis, subperiosteal abscess, orbital abscess, and cavernous sinus thrombosis. There may be overlap in the signs of symptoms of these conditions, but generally more severe systemic and focal findings point to infection that is greater in severity along that spectrum.