Hyperbaric Oxygen Therapy and Associated Cataracts

Excerpt

Hyperbaric oxygen therapy (HBOT) involves the administration of 100% oxygen at pressures exceeding 1 atmosphere absolute (ATA) for therapeutic purposes. A rare but potentially overlooked adverse effect of HBOT is the development of cataracts, which involves clouding of the eye's lens. This condition leads to significant loss of visual acuity and may progress to incapacitating blindness. Nuclear cataracts are the most prevalent type of cataracts that affect the central part of the lens and are commonly found in older populations. Although the exact cause of cataracts is not fully understood, recent evidence indicates that prolonged exposure to oxygen throughout one's lifetime is a primary contributing factor. This is particularly relevant when it comes to the increased partial pressure of oxygen that reaches the lens as the vitreous humor deteriorates with age.

Excessive exposure to HBOT sessions beyond the average duration of 20 to 50 sessions may increase the risk of permanent lenticular changes in the eye, such as cataracts. Experts attribute the presence of nuclear cataracts and a reversible myopic shift or negative change in refraction in patients undergoing HBOT to the likely cause of oxidative damage to the crystalline lens proteins. In an experiment involving guinea pigs exposed to hyperbaric oxygen, the average apparent diameter of proteins in the lens nucleus of animals treated with HBOT is almost double that of the control animals. These findings are similar to the aggregates identified in human nuclear cataracts.

Researchers have linked many reported symptoms to oxygen toxicity of the lens, which can cause myopia and the development and progression of cataracts. Commonly reported symptoms include eyelid twitching, blurry vision, and visual-field disturbances. Researchers believe that molecular oxygen in vivo induces the cross-linking of lens nuclear crystallins into large disulfide-bonded aggregates capable of scattering light. A similar process may be involved in forming human nuclear cataracts and could represent the end-stage of the frequently reported "myopic shift" observed in most patients undergoing 20 to 30 HBOTs. Although myopia changes are usually reversible within days to months after therapy cessation, the development of cataracts is generally permanent and might necessitate lens replacement surgery.