Mask squash

• orbital barotrauma is a potentially vision-threatening condition
  • is a complication of compressed air scuba diving and may be caused by improper mask fitting or poor diving technique
• ocular barotrauma (mask squeeze, mask barotrauma) may be explained using basic principles of hydraulics
  • according to Pascal's principle, pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid, as well as to the walls of the container
    • increasing water pressure with depth is transmitted to the relatively incompressible body tissues (fluids) including blood, blood vessels, interstitial tissues and skin
      • as the gas in the facemask is relatively compressible compared with the ocular tissues behind the mask, tissue displacement can occur traumatically at this gas-fluid interface subject to a pressure change
        • if equalization is not properly effected, the relative vacuum that occurs within the mask leads to a strong suction force onto the face and eyes (mask squeeze)
  • clinical features
    • in mild cases, an imprint of the mask on the face may be found.
    • more significant possible clinical features include:
      • relative drop in the extravascular atmospheric pressure may cause haemorrhages in ocular tissues such as skin, conjunctiva, retina and orbital structures
      • orbital haemorrhages may potentially threaten vision, and lead to permanent visual deficit from compressive optic neuropathy if not urgently addressed with orbital decompression
      • vitreous or intraretinal haemorrhages and a Purtscher-like retinopathy may also be seen
  • clinically it is important to differentiate the signs and symptoms of ocular barotrauma from decompression sickness or arterial gas embolism (AGE)
    • there are case reports of neurological symptoms e.g. diplopia, occurring secondary to ocular barotrauma (2)
      • the authors (2) noted that an AGE can present with a variety of neurologic symptoms such as loss of consciousness, dizziness, paralysis, abnormal sensation, blurred vision, or convulsions. Symptoms often present during ascent or within minutes of surfacing
        • in this case the patient's only complaint was diplopia
          • he had no other neurologic symptoms such as blurred vision, loss of consciousness, persistent symptoms of altered mentation, or numbness or weakness in an extremity, to suggest an AGE
          • in this case report the patient was noted to have proptosis of his right eye as well as periorbital petechiae and a subconjunctival hemorrhage on the right
          • a subconjunctival hemorrhage and petechia are common physical examination findings of mask barotrauma - the patient had an orbital CT scan done, and an orbital hemorrhage was noted
          • normal vision was restored when the haematoma and swelling resolved
      • both CT and MRI have been used to diagnose orbital barotrauma
• for further information on ocular and other injuries related to diving, the reader may refer to the Divers Alert Network at http://www.diversalertnetwork.org.

Reference:

• 1) Yeoh R et al.Barotraumatic ocular haemorrhage sustained while scuba diving. Clin Experiment Ophthalmol. 2008 Aug;36(6):581-2
• 2) Latham E et al. Diplopia due to mask barotrauma. Journ of Emerg Med 2008.
• 3) Andenmatten R et al. Orbital hemorrhage induced by barotraumas. Am J Ophthalmol 1994;118(4):536 -7.