Orbital cellulitis

• Infection of the deep soft tissue surrounding the eyeball, located posterior to the orbital septum - a medical emergency. It can progress rapidly and can lead to loss of sight and serious cerebral complications (such as meningitis and brain abscess).  Most cases are a consequence of acute or chronic bacterial sinusitis.

• Orbital cellulitis usually presents as an acute onset of unilateral eyelid swelling along with a red and painful eye. It is often associated with severe pain, blurred vision, diplopia, headache, fever, and systemic malaise.

• It is more serious than preseptal cellulitis and can be distinguished by pain with movement of the eye and vision changes. Some patients also have proptosis. 

Preseptal cellulitis (periorbital cellulitis)

• Caused by an infection anterior to the orbital septum. Causes include trauma and local infection (for example, a stye, impetigo, and dacryocystitis). Clinical findings do not always correlate with the severity of the condition.

• It can be difficult to differentiate between preseptal cellulitis and orbital cellulitis based on clinical observation alone. Both conditions may present with eyelid oedema and erythema.

• However, unlike orbital cellulitis, preseptal cellulitis does not cause visual impairment (including decreased visual acuity), limitation of extraocular movement, pain with eye movement, and protrusion of the eyeball (proptosis, although localized swelling may mimic proptosis).