Preseptal cellulitis occurs approximately 4 times more often than orbital cellulitis and is more frequent in children, particularly those younger than 5 years of age (Figure 30.2). Clinical features include swelling, erythema, and pain of the eyelid with the area of maximal inflammation indicating the likely source of infection. Inflammation may induce ptosis of the upper eyelid and may also be associated with tearing, conjunctival injection, and therefore accompanying blurred vision. This disease is often preceded by an upper respiratory infection, sinusitis, dental pathology, insect bite, trauma or surgery, or other infections in the surrounding area. Conjunctivitis may also develop into preseptal cellulitis. Preseptal cellulitis is often distinguished from deeper orbital infections clinically by the absence of globe displacement, restrictions in ocular motility, or raised ocular or orbital pressure. In uncertain cases, orbital or sinus computed tomography (CT) scans are obtained to rule out orbital cellulitis.

Orbital cellulitis (Figure 30.3) most commonly extends from infections of the ethmoid sinus, although it may also be acquired from other adjacent structures.^5,7 Less common causes include endophthalmitis, implants, retained foreign materials, or orbital tumors. Hematogenous spread is relatively rare. Orbital cellulitis occurs in all ages, but mostly in children 7 to 12 years old (older age than preseptal cellulitis) and has similar prevalence in males and females except in causes of trauma
where there is a male predominance. Children younger than 10 years are usually infected by a single aerobic pathogen, whereas older children and adults have more complex infections involving aerobic and anaerobic pathogens and are more likely to be polymicrobial.

Clinical features include pain, swelling, and erythema of the conjunctiva and eyelids, usually confined within the orbital rims. Between the bony orbital walls and the periorbita, or periosteum of the orbit, the potential subperiosteal space provides an area for potential accumulation and may lead to a subperiosteal abscess with mass effect similar to a tumor. Proptosis is usually present, and the globe may be displaced with the presence of an abscess. Abscesses larger than 10 mm and those that are in a nonmedial location should be evaluated for surgical drainage. Orbital inflammation may lead to raised intraocular pressure and restricted and painful eye movements with diplopia. Compressive optic neuropathy from orbital compartment syndrome can lead to severe permanent vision loss.

Venous drainage of the orbit through the cavernous sinus connects the orbit to the central nervous system, making severe intracranial infections a possible complication. Cranial nerves III, IV, V₁, and VI traverse the cavernous sinus and can be affected with the spread of orbital cellulitis. Intracranial extension with cavernous sinus thrombosis should be suspected when the patient has progressive cranial nerve palsies, fever, headache, and altered consciousness (see Table 30.1).