The communication will allow air to be forced from the sinuses into the orbit in the presence of a pressure gradient from forceful expiratory efforts, nose-blowing or even a sneeze. Orbital emphysema is typically a harmless disorder because air escapes as quickly as it enters the fracture site, and the increase in intraorbital pressure is usually transient, lasting for as long as the sneeze or nose blowing. However, when orbital soft tissues, such as fat, falls back on the sino-orbital communication, a one-way ball valve will be created, leading to the entrapment of air. When sufficient air accumulates, it will result in acute compartment syndrome and vascular compromise, causing complications including proptosis, visual impairment, central retinal artery occlusion, compressive optic neuropathy, and other severe complications caused by orbital compartment syndrome.There are three variations of orbital emphysema, namely palpebral emphysema, true orbital emphysema, and orbitopalpebral emphysema. Palpebral emphysema
Palpebral emphysema refers to emphysema of the eyelids alone. It is a rare kind of orbital emphysema which is usually caused by fractures of the lacrimal bone. The lacrimal sac ruptures as a result of the fracture, allowing air from the nasal cavity to enter the tissues of the eyelid. Alternatively, facial subcutaneous air may simply pass into the eyelids along fascial plane to produce palpebral emphysema. As long as the orbital septum is intact, air is confined in the eyelids. True orbital emphysema
True orbital emphysema occurs when there is air behind an intact orbital septum.
The pressure will be transmitted to orbital tissues and then to the globe, resulting in an increase in intraocular pressure which may cause visual loss when the nutrient vessels supplying the optic nerve are compressed. Stage IV
Stage IV orbital emphysema develops when the intraorbital air mass  results in an intraocular pressure of more than 60 to 70 mmHg. The significantly elevated intraocular pressure will lead to central retinal artery occlusion, which may result in permanent and irreversible damage to the retina. Clinical Diagnosis
The diagnosis of orbital emphysema is usually made by physical examination of the eyelids, and, or by computer tomography (CT). Physical examination
Physical examination of the eyelid can be done by the palpation for the pathognomonic cracking, crepitation, and tense tissue on the upper and lower eyelids. The findings of the examination are supported with the medical history of the patient and confirmed with orbital CT.

Computed tomography (CT)
Computed tomography is effective and sensitive in the diagnosis of orbital emphysema, as it can confirm the anatomical location and size of air, bony defects, indentation of the eyeball, and the condition of the optic nerve, as well as the presence of any extraocular muscle entrapment and herniation of preorbital fat into the sinus cavities. The location of the orbital emphysema is present near the site of the fracture. The scans are usually taken along the transverse plane. Transverse images allow the evaluation of fractures in medial and lateral orbital walls.