ESSEN, Germany, Feb. 26 (UPI) -- Patients who have undergone intraocular gas injection to treat retinal hemorrhages are at risk of blindness during airline travel, German researchers warn.

Researchers at the Essen University Clinic in Germany said that ophthalmologists inject gas into the eye mainly during the surgical treatment of retinal hemorrhages or injuries. The purpose of the gas is to help press the detached retina to the wall of the eye.

However, there is a risk of subsequent expansion of the gas bubble during airplane travel, at high altitudes, or under nitrous oxide anesthesia. This expansion can damage the retinal vessels, and the risk remains present for weeks after the surgical procedure, the researchers said.

The researchers told the journal Deutsches Arzteblatt International that ophthalmologists should inform patients before any operation of this type about the possibly dramatic consequences of air travel, travel to high altitudes and nitrous oxide -- laughing gas -- anesthesia.

Three months after an intraocular gas injection there should be no risk for the eye deriving from the remaining gas bubble, the researchers said.