**6. Epidemiology of orbital cellulitis**

Orbital complications of sinusitis have been reported to range anywhere between 0.5 to 3.9%. [1], [17], [27] However, the incidence of abscess formation vary considerably from 0-25% in the reported series. [15] No cases of abscess formation was reported in the published series from the Children's Memorial Hospital in Chicago including 87 patients with orbital cellulitis and from Children's Hospital in Pittsburgh including 104 orbital celulitis cases. [28], [29] On the other hand, a larger study of 6,770 patients from the Hospital for Sick Children in Toronto revealed that 2.3% developed orbital complications; of which 10.7% had abscess formation. [19] Another study reported 20.8% incidence of abscess formation among the 158 patients admitted for orbital cellulitis. There was a 20.8% incidence of abscess formation. [30] Among other series which has reported orbital complications of sinus disease, the incidence of abscess formation had varied from 6.25 to 20 % to as high as 78.6%. [18], [31], [32] One may attribute differences among these studies due to the inclusion criteria, age group and the severity of the complications studied by these authors. The incidence of major complications following sinusitis may be low, however such complications may be associated with considerable morbidity and mortality. [8], [15] According to the published report, in the pre-antibiotic era, orbital cellulitis resulted in death from meningitis in 17% of cases and blindness in 20%. [6] However, in the antibiotic era, incidence of menengitis was reported as 1.9% in patients with orbital cellulitis, despite prompt treatment with systemic antibiotics. [33]

**Figure 9.** External photographs as well as CT-scan (axial and coronal views) of a 7-year-old boy who presented with upper respiratory infection followed by painful diplopia, left eye proptosis and decreased vision. His symptoms did not improve with a course of systemic antibiotics. This patient required drainage of his orbital abscess which resulted in immediate resolution of his symptoms.

In-spite of systemic antibiotics and surgical intervention, orbital abscesses may have devas‐ tating outcome. [15] According to the series in which final visual results have been reported, a significant percentage of patients have been left with non-seeing eyes ranging anywhere from 7.1% to as high as 23.6%. [10] Visual loss in these cases have been attributed to optic atrophy, central retinal artery occlusion, or exposure keratopathy with corneal ulcer formation. [8], [10], [19] Some of the other hypothesized mechanisms of vision loss are septic optic neuritis, embolic or thrombotic lesions in the vascular supply of the optic nerve, choroid or retina. It has been postulated that delayed medical and surgical intervention may produce unacceptable visual outcome. [19], [20], [22]- [25] Among our 218 patients with diagnosis of orbital cellulitis, there were 116 cases of radiologically confirmed subperiosteal abscess, (Figure 9), 87% of them required drainage, and the remaining 13% were observed closely until their resolution while those patients were being treated with systemic antibiotics. [8] Thirty-nine eyes (17.8%) had endophthalmitis causing orbital cellulitis which required evisceration (9.6%) or enucleation (8.2%). Seven orbits required exenteration and 6 infected orbital implants had to be removed. Six patients had dacryocystitis that required a dacryocystorhinostomy to treat orbital cellulitis in addition to the administration of systemic antibiotics. [8]
