My optician explained it to me this way. The idea of removing extended wear lenses is do to the oxygen or lack of at altitude. The higher you go the harder for your eyes to breath. Long term effect is damage to the eyes that can eventually lead to not being able to wear contacts. This is in only a very few cases though. I personally have been wearing contacts (extended wear) for the last 10 years flying helicopters at altitudes as high as 10,000 ft. with the door off and have had no deterioration of vision and no odd side effects beside occasional drying. All depends on the person and their conditions I guess