20 / 20
Which of the following problems can be caused by wearing contact lenses?
  • A
    A reduction in colour vision, especially at high altitudes.
  • B
    Poor peripheral vision and occasional misting.
  • C
    The lenses may become dislodged when the humidity is too high.
  • D
    Increased corneal damage due to mild hypoxia and dehydration.


Contact lenses provide better peripheral vision and are, therefore, preferred by many pilots. But there are a few things to consider:

Aircrews spend much of their flying time at cabin altitudes of 8 000 ft. At these altitudes, substantially less oxygen is available relative to sea level. Since the amount of oxygen passing through a contact lens is directly related to the partial pressure of oxygen in the surrounding air (the cornea does not have its own blood supply), the amount of oxygen available under a contact lens will also diminish at higher altitudes.

In addition, low cabin humidities may dehydrate soft lenses, inducing a further decrease in oxygen available beneath these lenses by as much as 15 percent. Such reductions in oxygen availability may result in hypoxia with consequent corneal edema and other stresses to ocular physiology.

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