Oxygen toxicity or oxygen toxicity synrome (also known as the "Paul Bert effect" or the "Lorrain Smith effect") is severe hyperoxia caused by breathing oxygen at elevated partial pressures. These above-normal concentrations of oxygen within the body can cause cell damage in two principal regions: the central nervous system (CNS); and the lungs (pulmonary). Over time, it can also cause damage to the retina and may be implicated in some retinopathic conditions.