Ophthalmic disorders and flying

• eye surgery or penetrating eye injury - flying is contraindicated for at least seven days. Specialist opinion must be sought
  
  
• retinal surgery - requires specialist opinion. It may take two to six weeks for intraocular gas to be absorbed sufficiently to allow flying (see table below)

The following table is provided as a guide only to the timeframe that should elapse between a medical event and the intended flight. The timeframes may be changed following considered medical assessment of a specific case (3,4):

Ophthalmological procedures for retinal detachment also involve the introduction of gas by intra-ocular injections, which temporarily increase intra-ocular pressure (3)

• depending on the gas, it may be necessary to delay travel for approximately 2 weeks if sulphur hexafluoride (SF6) is used and 6 weeks with the use of perfluoropropane (C3F8). For other intra-ocular procedure and penetrating eye injuries, 1 week should elapse before flying

For up to date advice then check current guidance (3,4) before advising on fitness to fly.

Physiology of Changes of Intraocular gas volumes with changes in atmospheric pressure:

Altitude-associated changes in the volume of intraocular gas bubbles can be explained by Boyle’s law (P1V1 = P2V2) where P1 = first pressure, V1 = first volume, P2 = second pressure, V2 = second volume

• Boyle's Law - the absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system
• the equation states that the product of pressure and volume is a constant for a given mass of confined gas and this holds as long as the temperature is constant. For comparing the same substance under two different sets of conditions, the law can be usefully expressed as: P1V1 = P2V2
  • this equation shows that, as volume increases, the pressure of the gas decreases in proportion. Similarly, as volume decreases, the pressure of the gas increases
    
• decreases in absolute intraocular pressure (atmospheric pressure + intraocular pressure (IOP)) are observed as altitude increases, due to the falling surrounding atmospheric pressure (5,6)
  • concurrently, and in accordance with Boyle’s law, the intraocular bubble expands
    • using a rabbit model, it was demonstrated that the recorded fall in absolute intraocular pressure lags slightly behind the drop in atmospheric pressure
    • the investigators demonstrated that the larger the volume of intraocular gas, the greater this lag
    • the delay in pressure equilibration causes the elevated IOP readings that are observed with increases in altitude

Cabin pressurization:

• a critically important factor in determining of the risk of air travel
• in commercial aircraft cruise at high altitudes (typically 36,000-40,000 feet), and have cabin pressurization systems that protect passengers and crew from the physiological challenges associated with decreased environmental pressures
• aircraft cruising at altitudes of 36,000–40,000 feet have an equivalent effective cabin altitude of 6,000–8000 feet above sea level
  • regulations set by the Federal Aviation Administration in the US stimulate that cabin altitude should not exceed 8000 feet during normal operations (7)

Reference:

• Notes:
  • patients must have no air or gas trapped in the eyeball
  • these are only guidelines and each airline has its own regulations and medical standards

Reference:

1. 'Medical guidelines for air travel', Aviation, Space and Environmental Medicine, October 1996, 67, 10, 11.
2. Doctor (April 2005). Ready Reckoner - Fitness to fly.
3. Civil Aviation Authority. Fitness to Fly (Accessed 16/9/2020)
4. International Air Transport Association. Medical Manual 11th Edition (2018).
5. Lincoff H, Weinberger D, Reppucci V, Lincoff A. Air travel with intraocular gas. I. The mechanisms for compensation. Arch Ophthalmol (Chicago, Ill 1960). 1989;107(6):902–906
6. Foulsham W et al. Altitude-associated intraocular pressure changes in a gas-filled eye. Retin Cases Brief Rep 2020 : 10.1097/ICB.0000000000000852.
7. Bagshaw M Commercial aircraft cabin altitude. J R Soc Med 2007;100(2):64