This is due to an increase in the refractive power of the lens, since axial length and keratometry readings do not reveal a corneal or length basis for a myopic shift. It is usually reversible with time.A possible side effect of hyperbaric oxygen therapy is the initial or further development of cataracts, which are a increase in opacity of the lens of the eye which reduces visual acuity, and can eventually result in blindness. This is a rare event, associated with lifetime exposure to raised oxygen concentration, and may be under-reported as it develops very slowly. The cause is not fully understood, but evidence suggests that raised oxygen levels may cause accelerated deterioration of the vitreous humour due to degradation of lens crystallins by cross-linking, forming aggregates capable of scattering light. This may be an end-state development of the more commonly observed myopic shift associated with hyperbaric treatment. Mechanism
The biochemical basis for the toxicity of oxygen is the partial reduction of oxygen by one or two electrons to form reactive oxygen species, which are natural by-products of the normal metabolism of oxygen and have important roles in cell signalling. One species produced by the body, the superoxide anion (O−2), is possibly involved in iron acquisition. Higher than normal concentrations of oxygen lead to increased levels of reactive oxygen species. Oxygen is necessary for cell metabolism, and the blood supplies it to all parts of the body.
In either case, unless there is a prior history of epilepsy or tests indicate hypoglycaemia, a seizure occurring in the setting of breathing oxygen at partial pressures greater than 1.4 bar (140 kPa) suggests a diagnosis of oxygen toxicity.Diagnosis of bronchopulmonary dysplasia in newborn infants with breathing difficulties is difficult in the first few weeks. However, if the infants breathing does not improve during this time, blood tests and x-rays may be used to confirm bronchopulmonary dysplasia. In addition, an echocardiogram can help to eliminate other possible causes such as congenital heart defects or pulmonary arterial hypertension.The diagnosis of retinopathy of prematurity in infants is typically suggested by the clinical setting. Prematurity, low birth weight, and a history of oxygen exposure are the principal indicators, while no hereditary factors have been shown to yield a pattern. Prevention
The prevention of oxygen toxicity depends entirely on the setting. Both underwater and in space, proper precautions can eliminate the most pernicious effects. Premature infants commonly require supplemental oxygen to treat complications of preterm birth. In this case prevention of bronchopulmonary dysplasia and retinopathy of prematurity must be carried out without compromising a supply of oxygen adequate to preserve the infants life. Underwater
Oxygen toxicity is a catastrophic hazard in scuba diving, because a seizure results in high risk of death by drowning. The seizure may occur suddenly and with no warning symptoms. The effects are sudden convulsions and unconsciousness, during which victims can lose their regulator and drown.