Hyperbaric Related Myopia and Cataract Formation

Issues of Concern

Hyperbaric Myopia

One of the most commonly observed side effects in patients receiving prolonged HBOT is hyperoxic or hyperbaric myopia. Myopia, or “nearsightedness,” is a refractive disorder of the eye that often arises from either of 2 mechanisms. The first is axial elongation of the eye, measured from the posterior cornea to the retina, which prevents accurate image focus on the retina. The second is increased refractive power of the lens or cornea, resulting in anterior displacement of the focal point relative to the retina. In both cases, image focus occurs anterior to the retina, resulting in blurred vision. Visual disturbance is more pronounced with distant objects.

Many cases of myopia are anatomic in origin. However, acute myopic shifts in vision may have different etiologies. Such changes are often observed in hyperosmolar states, particularly with medications causing miosis and ciliary spasm. Myopic shifts are also common in the early stages of cataract development.[8][9]

Progressive myopic changes in the eye are a complication of repetitive HBOT. The exact mechanism remains incompletely understood, but oxygen toxicity is thought to induce changes in the crystalline lens, leading to increased lens rigidity and increased refractive power. The ultimate effect is a myopic shift with patient-reported blurred vision. Most myopic changes are reversible after cessation of therapy. Many studies report persistence of this effect for days to months. In a study by Lyne involving 26 patients undergoing HBOT at 2.5 atm for more than a month, 18 patients developed myopic changes ranging from 0.5 to 5.5 diopters. Reversal of myopia occurred rapidly within the first few weeks and then progressed more slowly over months, up to a year. Patients underwent pretreatment and follow-up assessments, including refraction studies, axial length measurements, keratometry, fundus examination, and tonometry. Examination results revealed no additional ocular effects of HBOT and suggested that observed myopic changes were attributable to lens alterations.[10]

Another study conducted by Palmquist et al involved 25 patients with daily exposures ranging from 150 to 850 at 2 to 2.5 atm. Myopic changes occurred in 24 of 25 patients, though additional ocular changes were also observed. These additional changes are discussed in the section regarding cataract formation. The study also suggested a possible increased risk of irreversible refractive changes when the number of therapies exceeds 100. Standard HBOT practice in the US typically utilizes 20 to 50 treatments.[11]

A study by Evanger et al suggested that increased oxygen delivery across the cornea, in addition to arterial circulation, may be a major mechanism underlying lenticular oxygen toxicity observed during HBOT. The study compared 20 patients receiving oxygen via hood delivery with 12 patients receiving oxygen via oronasal mask. Patients receiving oxygen via hood, with greater ocular oxygen exposure, demonstrated a higher incidence of myopia, greater refractive changes, and longer recovery time after cessation of therapy.[12][13] Evidence also suggests that HBOT at higher pressures may increase the incidence and severity of myopia.

Cataract Formation and Progression

Cataract formation and progression are known but less common complications of HBOT. A cataract is an opacity of the crystalline lens that can impair vision and lead to blindness. Major risk factors for cataract formation include increasing age, smoking, alcohol consumption, UV exposure, diabetes, prolonged steroid therapy, and malnutrition. Although exact mechanisms are incompletely understood, cataracts are believed to result from oxidative and toxic insults to the crystalline lens. Cataract development is less likely within the standard duration of HBOT. However, when cataracts develop or progress, lens changes are irreversible and may require surgical lens replacement.

In the study previously mentioned by Palmquist et al, 15 patients had clear lenses with no evidence of cataract prior to therapy. Nuclear cataracts developed in 7 of these 15 patients, with the first evidence appearing at 150 treatments. These changes were not fully reversible after cessation of prolonged therapy.

Cataract formation is generally considered to occur only in extreme cases involving HBOT. This view is supported by multiple studies, including the Lyne research, in which patients underwent extensive examinations that revealed no cataract formation or progression of existing cataracts after more than a month of treatment. As mentioned, the most common hyperbaric regimen in the US typically consists of 20 to 50 treatments. The risk for permanent lenticular changes, including cataract formation, appears to increase beyond standard treatment duration.

A reported exception involved a 49-year-old woman who developed cataracts after only 48 treatments. No identifiable risk factors for cataract development were present, including diabetes, prolonged UV exposure, or steroid therapy. Available evidence suggests that certain patients may have predisposing conditions that contribute to earlier cataract formation within standard treatment duration. Hyperbaric cataract formation may be a more severe manifestation of oxygen toxicity on the same spectrum as lenticular changes observed in hyperbaric myopia.

Evidence from animal studies suggests that HBOT accelerates normal age-related changes in the lens, including αA-crystallin truncation in the lens nucleus. In essence, hyperbaric oxygen accelerates lens aging, leading to cataract formation.[14][15]

Clinical Significance

Patients should be provided information regarding the risk of temporary myopic changes in vision and permanent cataract formation during informed consent counseling and prior to initiation of HBOT. Although guidelines have not been established, baseline ophthalmologic examination may be considered to detect preexisting lenticular pathology and monitor for progression of visual disturbances. This examination may be particularly beneficial for patients at increased risk of cataract formation, including individuals who have diabetes, are older than 50 years, have an extensive smoking history, receive steroid therapy, and have prior radiation exposure.

Baseline examination of visual acuity, along with serial monitoring, may detect myopic changes. Patients should be informed that these manifestations are usually reversible within days to months after cessation of therapy. Depending on severity, most patients do not require prescription lenses. Given the transient nature of HBOT-related myopia, commercially available adjustable glasses may be used. Lens correction may be adjusted as myopia develops during therapy and subsequently regresses after cessation of HBOT. However, cataract formation is usually permanent and typically requires lens replacement surgery. Given the high success rate of cataract surgery, this adverse effect is generally considered manageable. HBOT should not be discontinued when clinically indicated solely due to the development of myopia or cataracts, given the relatively benign and manageable nature of these effects.

Other Issues

Optic neuritis has historically been considered a contraindication to HBOT. However, several studies and case series in the literature demonstrate benefit, or at least no harm, from the use of HBOT in this condition.[16][17][18][19]

Enhancing Healthcare Team Outcomes

HBOT has been shown to have detrimental effects on the eye, manifesting primarily after repeated sessions. Insufficient evidence supports cataract or glaucoma development after a single session. Patients undergoing repeated HBOT should receive follow-up with an ophthalmologist and an internist to assess for ocular symptoms. Modifiable risk factors for eye disease should be addressed, and patients should be encouraged to maintain a healthy diet, wear sunglasses when outdoors, and avoid smoking. Healthcare workers should avoid prescribing HBOT without a valid clinical indication.

Nursing, Allied Health, and Interprofessional Team Interventions

In multiplace chamber settings, oxygen delivery via mask rather than hood appears to reduce the myopic effects of HBOT. This approach has been associated with a lower incidence of refractive changes.[20]

Nursing, Allied Health, and Interprofessional Team Monitoring

Hyperoxic myopia and likely cataract formation can also occur in divers. Visual acuity monitoring and periodic ophthalmic examinations are required, particularly in professional divers.[21]