Ocular effects of hyperbaric oxygen therapy

Introduction

Hyperbaric Oxygen Therapy (HBOT) is a therapeutic procedure that involves the exposure of a patient to 100% oxygen at pressures greater than atmospheric pressure at sea level [1]. This elevated concentration of oxygen can enhance the body’s natural healing process and is used to treat various medical conditions. The fundamental premise behind HBOT is to increase the amount of oxygen in the bloodstream, thereby accelerating the healing of tissues and enhancing the body’s innate ability to repair itself [1]. HBOT is typically administered inside a specially designed chamber where the patient breathes pure oxygen. The elevated atmospheric pressure inside the chamber can be adjusted depending on the specific treatment requirement [1].

HBOT has gained considerable recognition in the medical community for its therapeutic applications. The Undersea and Hyperbaric Medicine Society, a leading authority in this field, has officially endorsed HBOT for 14 medical conditions supported by scientific and clinical evidence [2]. Preliminary studies in ophthalmology suggest potential ‘off-label’ safe applications of HBOT, including central retinal artery occlusion, traumatic optic neuropathy, and retinal detachment [3]. Conversely, HBOT was found to not be beneficial in treating glaucomatous eyes and may come along with potential side effects such as myopic shifts [4]. We have summarized the key ophthalmic HBOT literature in Table 1.

Table 1.

Hyperbaric oxygen therapy in ophthalmology literature.

Authors	Key Findings	URL Reference
Altintas et al. [7]	Case reports showing that early administration of hyperbaric oxygen therapy (HBOT) within 24–48 h of acute central retinal artery occlusion (CRAO) significantly improves visual outcomes and may reverse retinal ischemia, presenting a promising treatment approach for this sight-threatening condition.	https://www.clinophthaljournal.com/articles/ijceo-aid1003.pdf
Rozenberg et al. [10]	HBOT led to significant improvement in best corrected visual acuity (BCVA) compared to standard of care (SOC) in patients with central retinal artery occlusion (CRAO), resulting in better final BCVA outcomes after adjusting for confounding factors.	https://pubmed.ncbi.nlm.nih.gov/34140653/
Soares et al. [11]	HBOT was beneficial in improving visual outcomes in patients with central retinal artery occlusion (CRAO), as evidenced by significant improvements in BCVA and normalization of fluorescein angiography (FA) results in two cases.	https://pubmed.ncbi.nlm.nih.gov/28500127/
Hwang et al. [15]	HBOT showed promising results in improving visual acuity and color vision in patients, with sustained improvements observed even after discontinuation of HBOT.	https://iovs.arvojournals.org/article.aspx?articleid=2373489
Cifu et al. [16]	HBOT at either 1.5 or 2.0 atmospheres absolute (ATA) equivalent did not significantly impact post-concussive eye movement abnormalities in military servicemembers with mild traumatic brain injury (TBI), as compared to a sham-control group.	https://pubmed.ncbi.nlm.nih.gov/25436771/
Bennett et al. [17]	Myopic shift, a common occurrence following HBOT, is more significant when using a hood system than an oronasal mask, and recovery is slower and less complete with the hood, suggesting the preferential use of an oronasal mask in an air environment when possible.	https://pubmed.ncbi.nlm.nih.gov/31828742/
Evanger et al. [18]	HBO can induce a temporary myopic shift, which is more pronounced when administered with a hood system compared to an oronasal mask. However, this myopic shift gradually recovers within 10 weeks, and no significant changes in crystalline lens transparency were observed.	https://pubmed.ncbi.nlm.nih.gov/15291940/
Evanger et al. [19]	Myopic shifts were observed in phakic eyes but not in pseudophakic eyes during HBO therapy, suggesting that these refractive changes are primarily attributed to changes in the crystalline lens.	https://pubmed.ncbi.nlm.nih.gov/21399553/

Retinal detachment and Central Retinal Artery Occlusion

Patients with sickle cell anaemia often experience complications like proliferative retinopathy, eventually resulting in a retinal detachment [5]. Traditional treatment methods, such as scleral buckling procedures, are poorly effective as the sickling of red blood cells hampers the circulation in the eye’s anterior segment during surgery [6]. Performing a modified scleral buckling procedure within a hyperbaric oxygen chamber was found to prevent the complications related to sickling, ensuring improved outcomes [7].

Central Retinal Artery Occlusion (CRAO) is an acute ophthalmic emergency characterized by rapid, painless vision loss [8]. It presents a significant clinical management challenge due to the limited effectiveness of current treatments. However, emerging evidence suggests that HBOT is a promising intervention [9]. In patients treated with HBOT, no complications, such as neovascularization, were observed, attesting to the safety of this approach [7]. A comparative study confirmed the potential advantages of HBOT, showing superior Best-Corrected Visual Acuity (BCVA) in CRAO patients treated with HBOT compared to those receiving standard care alone [10]. The physiological mechanism underlying these benefits appears to be hyperoxia-induced rapid restoration of retinal oxygen levels, thereby reducing the risk of retinal cell death and improving overall retinal function [11]. Objective measures, including BCVA and fluorescein angiography, further substantiated the visual improvements associated with HBOT [11].

Intraocular pressure and glaucomatous eyes

While HBOT is a recognized treatment for hypoxia-linked conditions, its implications on intraocular pressure (IOP) and eye health are multifaceted. While HBOT has been shown to reduce IOP in healthy subjects, its effects on glaucomatous eyes are uncertain. Additionally, the method of HBOT administration - hood versus oronasal mask—can influence its ocular impact. Hood administration, which involves exposing the eye directly to higher oxygen levels, can elevate the risk of oxidative damage, suggesting that oronasal mask delivery might be safer. Indeed, as HBOT’s popularity grows, it is crucial to approach its application cautiously, especially for patients with pre-existing ocular conditions [12]. Further research will be required to determine the effects of HBOT on the translaminar pressure gradient [13, 14].

Traumatic optic neuropathy and eye movement irregularities

While HBOT shows promise in improving visual outcomes for acute post-surgical or post-traumatic optic neuropathy, its efficacy in treating eye movement irregularities related to mild traumatic brain injury (mTBI) has been proven in a study by Hwang et al. Between 2008 and 2009, four patients with acute optic neuropathy were treated with HBOT and high-dose intravenous corticosteroids within 24 h of injury. The results indicated improvements in visual acuity and color vision, which stabilized, negating the need for further HBOT sessions [15].

Contrastingly, a comprehensive study at the Naval Medicine Operational Training Center involving 60 military servicemembers with at least one mTBI found no significant effects of HBOT on eye movement irregularities. Utilizing a validated computerized eye tracking method, various eye movements such as fixation, saccades, and smooth pursuit were analysed before and after HBOT sessions. Both between-group and within-group analyses revealed no significant improvements in eye movement irregularities when HBOT was compared to a sham control [16].

Change in refraction

Refractive changes have been reported as a potential ocular side effect of multiple exposures and dosage of HBOT [17]. The study by Evanger et al. studies the use of HBOT on the crystalline, which overall manifests with changes in refraction over the treatment [18]. In this study, the myopic shifts have been found to be attributable to changes in the crystalline lens. This mechanism has been attributed to the oxidative stress that causes an aggregation of proteins in the lens nucleus, inducing opacification of the lens [19]. More frequent vision testing may be required in this population to detect these changes earlier [20–22].

Conclusion

The future of HBOT in ophthalmology is promising, particularly for conditions where traditional treatments fall short. Real-time monitoring could help tailor treatments to individual patient needs, reducing side effects. Advancements in protocol and delivery systems are expected to mitigate these risks (such as oxidative stress) over time. Overall, HBOT’s therapeutic potential, technological advancements, and improved safety protocols could make it a cornerstone of next-generation ophthalmic care.

Author contributions

MR: writing; EW, JO, and MM: writing and intellectual support; AGL: review and intellectual support.

Competing interests

The authors declare no competing interests.