Anterior Chamber Bubble Expansion With Decreases In Atmospheric Pressure

To examine the effects of reducing atmospheric pressure on the expansion behavior of an air bubble in the anterior chamber and intraocular pressure.

Department of Ophthalmology, Medical University of Vienna.

The anterior chamber of 36 human donor eyes were filled with either 30%, 50%, or 90% air. All eyes were imaged before and after gas filling (OCT). The eyes were placed in a clear, airtight box in front of the OCT. In the box, the eyes were connected to a pressure measurement device  to monitor IOP. The box itself was connected to a compressor with an interposed throttle valve, allowing control over the change in atmospheric pressure. The atmospheric pressure inside the box was reduced to 750 hPa to mimic the minimum cabin pressure of commercial air travel. Pressure was reduced by 10.9 hPa/minute, equivalent to an ascent of 91 meters per minute (standard ascent rate for commercial air travel). OCT imaging was repeated every minute.

Air bubbles expanded in accordance with Boyle's law (P1V1=P2V2). However there was a slight but consistent a time lag to be observed between a fall in atmospheric pressure and the gas bubbles' expansions. This lag was longer in eyes with larger air bubbles.

Intraocular pressure rose linearly in all groups, the rate of which was consistently faster in eyes with larger air bubbles. The maximum IOP was 103mmHg in an eye with a gas filling of 90% at minimal atmospheric pressure. 

Eyes with 30% air filling experienced an increase in IOP of up to 25mmHg at a minimum atmospheric pressure of ca 830 hPa. With an air filling of 50%, a reduction to ca 900 hPa is tolerated well. Eyes with 90% tolerate only small changes in pressure (ca 50 hPa decrease).