Oxygen toxicity

Oxygen toxicity is a possible side effect of exposure to high pressures of high concentrations of oxygen over long periods of time, typical in treament in a hyperbaric chamber or in an incubator for premature infants. It can also occur in scuba divers.
High oxygen levels can affect the nervous system, lungs, and eyes by destroying cells. These manifest themselves as symptoms in those area as nerves, lung tissue and the retina slowly degrade. If not reversed in time, the symptoms can be permanent.
As a precaution, patients on high oxygen therapy are usually exposed to normal air during part of their treatment regimen. However, if symptoms present in a patient under high pressures of oxygen, the pressure should be slowly reduced to normal and air should be substitute for oxygen.
Oxygen toxicity at Wikipedia