Periorbital cellulitis, also known as preseptal cellulitis, is a bacterial infection causing visible inflammation and swelling of the eyelid and surrounding soft tissues. Anatomically, the infection remains anterior, or in front of, the orbital septum, a thin membrane separating the eyelid from deeper eye socket structures. This infection develops when microorganisms invade the skin barrier or spread from a nearby source, leading to characteristic redness and puffiness.
Primary Routes of Local Infection
The most frequent cause of periorbital cellulitis, particularly in children, is the direct entry of bacteria through a break in the skin near the eye. Minor injuries such as scratches, scrapes, or abrasions provide an easy pathway for common skin bacteria to penetrate the underlying soft tissue.
Insect bites are another common local entry point, as the biting or subsequent scratching introduces bacteria into the tissue. Pre-existing superficial skin infections can also act as a reservoir for bacteria that track into the periorbital area. Examples include impetigo or the secondary infection of a stye (hordeolum) or chalazion near the eyelid margin.
Bacteria may also spread from acute conjunctivitis (pink eye), where infectious agents travel backward from the eye’s surface into the surrounding skin. In all these cases, damage to the skin barrier allows the proliferation of bacteria.
Identifying the Specific Pathogens
The agents responsible for periorbital cellulitis are common bacteria found on the skin or in the respiratory tract. Staphylococcus aureus is frequently isolated, often originating from the skin or a localized wound. Methicillin-resistant S. aureus (MRSA) requires specific treatment protocols due to its resistance to many common antibiotics.
Streptococcus species, including S. pneumoniae and S. pyogenes, are also common. S. pneumoniae is often associated with infections spread from the sinuses or respiratory tract, while S. pyogenes causes skin and soft tissue infections.
Historically, Haemophilus influenzae type b (Hib) was a leading cause, especially in young, unvaccinated children. Widespread administration of the Hib vaccine has dramatically decreased the incidence in vaccinated populations. Most current cases are now caused by staphylococcal and streptococcal organisms.
Spread from Adjacent Regions and Contributing Factors
Beyond local inoculation, the infection can arise from the spread of bacteria from nearby anatomical structures, most often the paranasal sinuses. Acute sinusitis, particularly involving the ethmoid sinuses located close to the inner corner of the eye, is a common cause of periorbital cellulitis. The infection tracks forward from the sinus cavity into the periorbital tissues due to the thin bony separation, known as the lamina papyracea, or via small venous connections.
In rare instances, particularly in infants and individuals with systemic illness, the infection may arrive through hematogenous spread. This means the bacteria travel through the bloodstream (bacteremia) from a distant source, seeding the periorbital tissues. This route is less common than local entry or sinus spread but highlights the potential for a deeper, systemic origin.
Contributing Factors
Several patient factors can increase susceptibility to developing periorbital cellulitis following exposure. Young children, especially those under five years of age, are disproportionately affected, partly due to their less developed immune systems and a higher frequency of minor facial trauma. A recent upper respiratory tract infection (URI) also serves as a contributing factor, as it introduces bacterial pathogens into the nasal and sinus passages. Finally, any condition that compromises the immune system, such as poorly controlled diabetes or undergoing chemotherapy, reduces the body’s ability to fight off the initial bacterial invasion.