Andy C. O. Cheng
Dr Andy Cheng graduated from the Medical Faculty of the University of Hong Kong with honours and further attained the Master of Medical Science degree with distinction in HKU specializing in morphological science and neuroscience. He holds the Diploma in Practical Dermatology qualification from the Cardiff University. He is currently the Fellow of the Royal College of Surgeons of Edinburgh, College of Ophthalmologists of Hong Kong and Hong Kong Academy of Medicine. Dr Cheng is the Honorary Consultant Ophthalmologist of the Hong Kong Sanatorium & Hospital and the Honorary Clinical Assistant Professor of the Chinese University of Hong Kong. He has subspecialties interest in Orbit & Oculoplastic surgery and Neuro-Ophthalmology.
Orbital emphysema is an uncommon condition, which is defined as the presence of air within the fascial layers of the orbit . It occurs most commonly after orbital/facial trauma or surgery, e.g. dacryocystorhinostomy, orbital decompression and functional endoscopic sinus surgery. Rarely, it can occur with sinusitis (especially with gas-forming microorganisms), nose blowing, sneezing, during air travel with pressure changes or Valsalva manoeuvre [1–7].
Orbital emphysema occurs mostly from defects in the orbital walls, especially the medial lamina papyracea and orbital floor (Fig. 20.1). Air migrates from the ethmoid, the maxilla and, less commonly, the frontal sinus through the defect into the orbit. Air enters the orbit intermittently during episodes of acute rise in pressure in the respiratory passage, which can happen after nose blowing, coughing or sneezing . Serious orbital emphysema may result from a small fracture site or when orbital tissues fall back to the defect acting as a one-way valve . Subsequent pressure rise may build up within the orbit resulting in an orbital compartment syndrome (please see previous chapter). If not promptly identified and treated, it can result in severe and permanent visual loss. Fortunately, most cases of orbital emphysema are benign and self-limiting requiring only close monitoring and advice against nose blowing or deliberate Valsalva action .
Axial CT scan of orbit showing right orbital emphysema due to fractured lamina papyracea
Depending on the severity, orbital emphysema may present as an incidental finding in CT scan of the orbit in mild cases. In severe cases, it can present with symptoms and signs of orbital compartment syndrome, including acute proptosis, eyelid swelling, severe pain, diplopia with limited ocular motility and even severe visual loss. There may be associated eyelid emphysema with crepitus felt over the eyelids. The orbital pressure may be very high with “tightness” felt on retropulsion. The intraocular pressure may also be grossly elevated, documented to be >70 cm H2O in some cases . CT scan of the orbit may show pneumo-orbitae and tenting of posterior globe of less than 120°  (please see chapter on orbital compartment syndrome). The acute rise in orbital pressure may cause ischaemic optic neuropathy, central retinal artery occlusion and stretch and compressive optic neuropathy, resulting in permanent visual loss.