Viral infections of the orbit are uncommon and may mimic a bacterial cellulitis in early phases and hence need a high degree of suspicion, directed investigations, and appropriate management to prevent widespread damage and long-term sequelae. The most well-defined viral orbital infection is caused by herpes simplex virus (HSV) and herpes zoster virus (HZV) [1]. The varicella zoster virus can cause both chicken pox and shingles. In most of the cases, the primary infection usually occurs during childhood, following which the virus travels in a retrograde fashion to the dorsal root ganglia or sensory ganglia, where it may remain dormant for long periods. When the patient is immunosuppressed or when the virus-specific cell-mediated immunity decreases, it gets reactivated and travels along the trigeminal nerve or its branches to the orbit. Apart from the classical dermatomal pattern of skin lesions, orbital involvement may be in the form of retrobulbar neuritis, third, fourth, and sixth cranial nerve palsies manifesting with diplopia and ophthalmoplegia [1]. Most of these clinical features recover to a certain extent in 6–8 months, but may have a long-term sequelae [1].

Paraskevas et al. [2] described a case of a painful ophthalmoplegia with simultaneous orbital myositis with the involvement of the trigeminal nucleus and oculomotor nerve. Magnetic resonance imaging demonstrated abnormal signal intensity in recti muscles along with the trigeminal nucleus in brain stem. Serum and CSF were positive for HZV DNA, and the patient was effectively treated with acyclovir and methylprednisolone successfully. Rozenbaum O et al. [3] described a case of HSV-2-induced diffuse orbital cellulitis as a first presenting symptom of acute retinal necrosis. Although orbital inflammation resolved rapidly following initiation of antiviral, the intraocular inflammation worsened and the patient’s vision could not be salvaged. Tornerup et al. [4] similarly presented a case of acute retinal necrosis presenting with signs of orbital inflammation, proptosis, and optic neuritis. CT scan was suggestive of thickened optic nerves, and polymerase chain reaction isolated HSV-1 DNA from the vitreous samples. The patient was successfully treated with intravenous acyclovir and oral prednisolone. Lee MS et al. [5] based on their case suggested that retrobulbar neuritis can precede acute retinal necrosis in HIV+ patients.

With increasing incidence of HIV infections, newer features of orbital infections and presentations are being unraveled. In a large epidemiological study on ocular manifestations in AIDS, among the 553 patient studies, 3 patients each presented with retrobulbar neuritis, lateral rectus palsy, and ptosis secondary to involvement of oculomotor nerve [6]. Opportunistic infections like varicella zoster and orbital tuberculosis with their sequelae may occur when the CD4 counts drop below 500 cells per microliter [6]. HIV infection-related orbital involvement with malignancies like Kaposi sarcomas and lymphomas are well known. Scheschonka et al. [7] reported AIDS-related Kaposi sarcoma of the lacrimal gland and discussed the role of a high suspicion and imaging modalities in managing these cases. Rarely orbital complications with the use of antiretroviral drugs have been reported to cause enophthalmos due to atrophy of the orbital fat secondary to lipodystrophic effect of the drugs [8].

Numerous other viral infections rarely cause orbital infections notably Epstein-Barr virus, hepatitis B virus, hepatitis C virus, and dengue virus. Epstein-Barr virus (EBV) may involve the orbit through its role in promoting orbital and adnexal lymphomas. Chronic infections with EBV have been reported to present as orbital myositis in conjunction with a generalized myositis with ineffective immunotherapy and poor prognosis [9]. EBV has also been reported and quantified in certain idiopathic orbital inflammatory pseudotumors and may present with the entire spectrum of proptosis, diplopia, chemosis, and periocular edema [10].Chronic EBV infections have also been reported to cause orbital Langerhans cell histiocytosis in pediatric age group, presenting as bilateral proptosis with extensive orbital bony wall involvement [11].

Urticaria and periorbital edema can rarely be a prodromal presenting sign of an acute hepatitis B infection [12]. Numerous viral agents have been implicated in orbital neoplasia with their typical orbital symptomatology. Notable among these are hepatitis C virus, herpes simplex virus 8 (HHV-8), and human papillomavirus (HPV) [13, 14].

Mucormycosis, also known as phycomycosis or zygomycosis, is the most aggressive fungal orbital infection, most commonly seen in patients with diabetic ketoacidosis and occasionally in post-renal transplant patients [16, 17]. It is caused by fungi in the order Mucorales and species implicated include Mucor, Rhizopus, and Absidia [18]. The infection usually starts when the respiratory tract and sinuses are inoculated by the ubiquitous spores. In the event of immunosuppression, the hyphae of the organism tend to invade tissues and are characteristically known to invade blood vessels causing infarction and the typical black eschar [19]. Orbit and intracranial invasion is usually secondary to sinus infections, can be rapid, and lead to quick mortality if untreated. The earliest feature can be painful ophthalmoplegia with rapidly developing proptosis and orbital cellulitis and sudden loss of vision [16]. Imaging with a CT scan and MRI would demonstrate hazy sinuses with destruction of sino-orbital walls and soft tissue density alterations in the orbit.

Upon suspicion, a prompt multidisciplinary approach is needed. Tissues should be obtained for microbiology workup and histopathological examination. Diagnosis is clinched by demonstrating large nonseptate-branching hyphae. The underlying cause like diabetic ketoacidosis should be aggressively treated, and wide surgical excision with frozen section control is usually performed followed by thorough irrigation with antifungal agents along with their systemic use [20, 21]. On occasions exenteration and extended exenteration may have to be performed based on the extent of disease.

Aspergillus is a deuteromycete fungus and is ubiquitous in nature. It has septate hyphae, and Aspergillus flavus and A. fumigatus are commonly implicated pathogenic species (Fig. 34.1). Although routinely harmless, it is an opportunistic pathogen, known to occur in immunocompromised status and in drug addicts. Disseminated aspergillosis is rare and is not known to involve the orbit, since mortality occurs much before it invades the orbit [16]. Localized invasive sino-orbital aspergillosis is more common and may present with proptosis, dystopia, and painful ophthalmoplegia with an occasional fistula formation and fungal abscess [22–24].Although slow growing, if untreated, it may lead to widespread local invasion with catastrophic complications and death [22]. Diagnosis is based on tissue biopsy for microbiological workup (smears and fungal culture, polymerase chain reaction for fungal DNA) and histopathological diagnosis (Figs. 34.2 and 34.3). CT scans may show the involved sinuses, breach of sino-orbital walls, mass lesions, and extent of spread. Once established, if widespread locally, a surgical debulking followed by systemic antifungals like voriconazole for a prolonged duration (months) based on response should be initiated (Figs. 34.4, 34.5, 34.6, 34.7, 34.8, 34.9, and 34.10) [24].