Acute eyelid infection and orbital infection are characterized by various cardinal signs of inflammation including pain, redness, swelling, and warmth. Eyelid infection is more easily identified clinically with redness and swelling over the eyelid, whereas distinguishing orbital infection and orbital inflammation can sometimes be difficult as orbital infection and other orbital inflammatory processes can have similar presentation. Since the orbit is a confined space, swelling or edema secondary to any inflammatory process can lead to proptosis as well as compression of the structures within the orbit [1]. Typical presentations for orbital infection include red eye, proptosis, ophthalmoplegia, and pain. In severe cases, the eyeball and optic nerve can be compressed leading to choroidal folds or compressive optic neuropathy [2]. Performing a complete medical history, along with complete physical examination with visual acuity testing, and laboratory and radiologic testing will narrow down the differential diagnosis. Blood tests should be guided by clinical suspicion; these include complete blood count, erythrocyte sedimentation rate (ESR), C-reactive protein, antinuclear antibody (ANA), cytoplasmic antineutrophil cytoplasmic antibodies (C-ANCAs), rheumatoid factor (RF), serum protein electrophoresis, angiotensin-converting enzyme (ACE), and thyroid function studies. Radiologic orbital evaluation commonly involves computerized tomography (CT) scan or magnetic resonance imaging (MRI) with intravenous contrast and is very helpful to narrow down the differential diagnoses and assess the location and extent of the disease process. Patients with atypical presentation or those who are unresponsive to medical treatment may even require an orbital biopsy for pathological diagnosis [3]. Microbiological tests including Gram stain, culture, and sensitivity tests are helpful to identify the causative microorganisms and to guide the antimicrobial treatments. In cases of atypical infections, HIV infection or other causes of immunodeficiency status should be excluded [4].

Eyelid infection should be considered as the first differential diagnosis if a patient presented with redness, swelling, and pain over the eyelid. Allergic eyelid disorders including acute allergic edema can also have similar presentation, but patients with allergic eyelid disorder may have a history of insect bites, angioedema, urticaria, and occasionally drug usage. Patient may have itchiness in allergic eyelid disorder, especially in contact dermatitis. Moreover, allergic eyelid tends to be painless with the presence of pitting periorbital and lid edema. The differentiation is important as eyelid infection requires the use of antimicrobial medication, whereas antihistamine is required in case of acute allergic edema [5].

Acute eyelid and orbital infections are usually caused by viral or bacterial infection; fungal infection and atypical infection such as Mycobacteria infection tend to have different clinical presentation. The two most common forms of acute viral eyelid infections are herpes simplex and herpes zoster infection. Primary herpes simplex infection is caused by herpes simplex virus (HSV). This is typically affects children as unilateral condition. HSV eyelid infection may be more severe in those patients with atopic dermatitis and immunodeficiency status. The clinical features include crops of small vesicles which rupture, crust, and heal within a few days. Uncommon complications include follicular conjunctivitis and keratitis. The condition tends to be self-limiting and can be treated with acyclovir ointment [6].

Herpes zoster is a more common viral eyelid infection which is caused by varicella zoster virus (VZV). It typically affects elderly but may occur at earlier age and be more severe in immunocompromised patients. When this affects the first branch of the fifth nerve or trigeminal nerve, this is also known as herpes zoster ophthalmicus. The clinical features include pain in the distribution of first branch of the fifth nerve, a maculopapular rash over the forehead and eyelid which later became vesicles, pustules to crusting ulceration, and periorbital eyelid edema. In severe cases, this may cause scarring of the eyelid. Patients can have other ocular complications including conjunctivitis, keratitis, uveitis, scleritis, or even optic neuritis and cranial nerve palsy. The treatment includes the systemic antiviral agents such as acyclovir, valacyclovir, or famciclovir. Topical acyclovir or penciclovir cream and steroid-antibiotic combination ointment can be applied to the affected skin as well [6].

There are also various forms of bacterial eyelid infections; these include blepharitis, stye or infected chalazion, impetigo, erysipelas, and necrotizing fasciitis. Blepharitis is the commonest form of mild chronic eyelid infection and is related to poor lid hygiene, excessive meibomian gland secretion, and Staphylococci infection. In some cases, there may be eyelid hyperemia, telangiectasia, crusting, and redness suggestive of acute infective element. The treatment includes lid hygiene, antibiotic ointment, weak topical steroids, and artificial tear substitutes [7].

Stye is an acute infection of lash follicle unit caused by Staphylococci infection; sometimes this is associated with pustule formation. Chalazion is a chronic lipogranulomatous inflammation of the meibomian gland which produces a nodular lesion around the lid margin. Chalazion can be infected leading to a tender erythematous nodule. Both stye and infected chalazion can be treated with hot compress and topical antibiotics with or without steroid. Incision and drainage should be considered if there is abscess collection. Systemic antibiotics are required in case of secondary cellulitis [8].

Impetigo is the superficial skin infection caused by Staph. aureus or Strep. pyogenes. Children are more often affected, and patient may have erythematous macules which rapidly developed into vesicles and bullae. These vesicles and bullae will rupture and produce golden-yellow crust. The infection may spread into other parts of the face. Treatment includes the use of topical antibiotic and systemic antibiotic such as flucloxacillin or erythromycin [9].

Erysipelas, also known as St. Anthony’s Fire, is an acute subcutaneous cellulitis caused by Strep. pyogenes through a site of skin injury. This is characterized by a well-defined indurated erythematous subcutaneous plaque. The treatment is with oral antibiotics such as phenoxymethylpenicillin, amoxicillin with clavulanate, or ampicillin-sulbactam [5].

More severe form of eyelid infection can also be called preseptal cellulitis, and possible etiological factors include endogenous infection foci, trauma, postoperative wound infection, chalazion, or idiopathic in nature. Even though eyelid infections are often localized in nature, in severe cases, patient can potentially have systemic symptoms such as fever and elevated WBC count. If left untreated, these can cause postseptal orbital cellulitis or even systemic bacteremia [5, 10].

Necrotizing fasciitis is an extremely rare rapidly progressive infection with necrosis of tissue caused by Strep. pyogenes or occasionally Staph. aureus infection. This is characterized by blackish discoloration of skin due to tissue thrombosis with gangrene. Necrotizing fasciitis is a potentially vision threatening or even life-threatening condition and has to be treated aggressively with tissue debridement and systemic antibiotics [11].

There are various causes of orbital inflammatory diseases and can be broadly divided into infective and noninfective causes. Orbital cellulitis should be the first differential diagnosis whenever one is faced with orbital inflammatory process. Orbital cellulitis can be classified as preseptal or postseptal cellulitis. In case of orbital cellulitis, bacterial infection is more common than viral, fungal, or parasitic infection. Mycobacteria infection may occasionally be encountered and tends to have a more indolent course [12]. Orbital fungal infections such as mucormycosis and aspergillosis can have aggressive clinical behavior, and a high of suspicious is required for prompt diagnosis [13].