Asia
Hyperbaric
Centre
Who Is
This For?
One moment, the world is whole. Then a curtain comes down over one eye. No pain. No warning. Just vision, suddenly gone.
This is a central retinal artery occlusion — an eye stroke. The retina, like the brain, is nerve tissue. Starved of blood, it begins to die within hours. What happens in those hours decides what comes back.
At Asia Hyperbaric Centre, we deliver 99.5% medical-grade oxygen under pressure — feeding the retina through a back-door route that does not depend on the blocked artery [1]. It is a recognised emergency indication of the Undersea and Hyperbaric Medical Society [1]. If this is happening to you or someone near you right now, do not finish reading. Call us. Every hour matters [2] [3].
This emergency protocol is for people with a sudden, painless loss of vision in one eye, diagnosed — or suspected — as non-arteritic central retinal artery occlusion, where an eye specialist recommends hyperbaric oxygen as part of urgent care.
The detail that decides everything:
The clock. The evidence is unambiguous: outcomes are best when the first session begins within hours of symptom onset — ideally inside 8 to 12 hours, and still worthwhile inside 24 [2] [3] [4]. This is not a condition that books an appointment next week.
The diagnosis. CRAO is caused by a blockage, usually a small clot. If the cause is inflammation of the artery wall (giant cell arteritis), the emergency treatment is different — high-dose steroids — and an eye specialist must rule this out first [1].
The whole person. An eye stroke is a warning shot from the same blood vessels that feed the brain. Urgent stroke work-up runs alongside anything we do [1] [5].
A doctor's referral is required — in this emergency, it is typically the ophthalmologist or emergency physician who sees you first. We coordinate directly with them, the same day.
When to Consider HBOT
The Retina's Back-Door Oxygen Supply
The retina is the most oxygen-hungry tissue in the body, gram for gram. It normally feeds from two directions: the retinal artery from the inside, and the choroid — a dense vascular layer behind the eye — from the outside. In CRAO, the inside supply is blocked. The choroid remains. But at normal oxygen levels, it cannot carry the full load, and the inner retina begins to suffocate [1].
Breathing faster cannot fix this. Even breathing pure oxygen at normal pressure cannot deliver enough through that back-door route.
Inside the chamber, we change the physics. At 2.0 to 2.5 ATA, 99.5% medical-grade oxygen dissolves directly into the blood plasma, raising oxygen tension far beyond normal limits [1]. At that tension, the choroid's circulation can do something remarkable: supply the entire retina, from behind, around the blockage. Not forever — but long enough. Long enough for the body's own clot-clearing systems to reopen the artery, or for collateral flow to establish [1] [7].
That is the whole strategy, and it is honest: hyperbaric oxygen does not remove the clot. It keeps the retina alive while other processes remove it — and it preserves the margin of tissue that would otherwise be lost in the waiting [1].
The Science & Clinical Evidence
We do not make promises. The research does that. CRAO is a recognised UHMS indication [1], and its evidence has one dominant pattern: the earlier the session, the better the sight.
In a single-centre series of 41 people treated with hyperbaric oxygen, timing split the outcomes cleanly [3]:
70% vs 29% — the proportion achieving meaningful visual improvement when the first session began within 9 hours of symptom onset, versus after. — Maldonado et al., reported via American Academy of Ophthalmology, 2024–25 [3]
A UHMS-journal series of 38 people found the same gradient on the standard logMAR scale [2]:
0.9 logMAR — the average visual acuity improvement when sessions began within 8 hours — roughly three to five lines on the eye chart. Begun within 24 hours, improvement averaged 0.5 logMAR. The control for this disease — untreated CRAO — leaves 90% of people at 20/400 or worse [2] [8]. — Rozenberg et al., Undersea & Hyperbaric Medicine, 2023 [2]
The largest cohorts point the same way: 65% improved across 60 cases in one series [4]; the largest series of all, 128 people, confirmed meaningful recovery and added a practical insight — the retina's appearance, not the clock alone, marks the point of irreversibility [6]. And a 2026 meta-analysis found hyperbaric oxygen delivered visual gains comparable to intravenous clot-busting therapy, with a safer side-effect profile [9].
Where we are honest with you: there is no randomized trial of hyperbaric oxygen versus no treatment for CRAO — for an emergency this time-critical, one is nearly impossible to run ethically. One smaller meta-analysis found no benefit [10], and every positive series shares the same weakness: the people who arrive earliest do best, and they might have done better anyway. The evidence leans clearly toward benefit — but the honest sentence is this: hyperbaric oxygen is a reasonable emergency option with a strong timing signal, delivered alongside stroke work-up, not instead of it.
In this emergency, the schedule is set by the retina, not the calendar. Our protocols follow the parameters used in the published series and UHMS guidance [1] [2].
Oxygen Purity: 99.5% Medical-Grade Oxygen — pharmaceutical-grade purity certified under the Pharmacy and Poisons Ordinance (Cap. 138) [11].
Chamber Pressure: 2.0 to 2.5 ATA (Atmospheres Absolute) — the range used across the CRAO series [2] [3] [4].
Session Duration: 90 minutes at depth.
Frequency (emergency phase): The first session as soon as possible after presentation; sessions may run twice daily in the first critical days, then once daily, guided by visual response [2] [3].
Total Course: Varies with response — the published series range from a median of 3 sessions to around 9, continued until vision stabilises [2] [4]. Your ophthalmologist tracks the retinal appearance and calls the stop.
The Protocol
What To Expect
We understand that entering a hyperbaric chamber can feel unfamiliar. Our team is here to guide you through every step of the process, ensuring you feel comfortable, safe, and supported.
Step 1 — The Briefing & Preparation: Before your first session, our technician will walk you through the safety protocols. You will change into 100% cotton clothing (provided) to eliminate static risk. No electronics, watches, or oil-based cosmetics are allowed inside the chamber.
Step 2 — Pressurisation: As the chamber pressurises over 10-15 minutes, you will feel a sensation in your ears similar to descending in an airplane. Our technician will coach you on simple techniques to clear your ears. Once at depth (2.0-2.4 ATA), you will breathe 99.5% pure oxygen through a comfortable hood or mask. You can read, rest, or watch a screen during the 90-minute session.
Step 3 — Depressurisation & Next Steps: The chamber will slowly depressurise over 10-15 minutes. Once open, you can return to your normal daily activities immediately. Our technician will examine your wound site and coordinate with your primary wound care team to track your progress.
FAQ
How many sessions before I notice a difference?
In this condition, the question is not how many — it is how soon. Many people report some change within the first few sessions; the published series range from a median of 3 sessions to around 9, continued until vision stabilises [2] [4]. Your ophthalmologist measures the response, not us.
I lost vision hours ago. Is it too late?
Earlier is better — that is what every study shows — but "too late" is a retinal diagnosis, not a clock reading. Meaningful recovery has been documented well beyond 12 hours, and the retinal appearance predicts reversibility better than time alone [2] [5] [6]. Do not self-triage. Contact us and your eye specialist now, and let the examination decide.
Will I get my vision back?
No honest provider can promise that. Untreated, about 9 in 10 people with CRAO are left with severe vision loss [8]. With hyperbaric oxygen, the published series report meaningful improvement in roughly 6 to 7 in 10 — rising to 7 in 10 when treatment begins within about 9 hours [2] [3] [4]. Those are real numbers, and they are also averages. What we can promise is speed: if you call, we move today.
UHMS. Arterial Insufficiencies (Central Retinal Artery Occlusion). UHMS Hyperbaric Oxygen Therapy Indications, 15th Edition. Undersea and Hyperbaric Medical Society. UHMS Official Indications
Rozenberg E, et al. Hyperbaric oxygen therapy for central retinal artery occlusion: visual acuity and time to treatment. Undersea Hyperb Med. 2023;50(3). UHMS Journal
Maldonado R, et al. Hyperbaric oxygen therapy for early CRAO (retrospective cohort, 41 patients; 70% vs 29% meaningful improvement within/after 9 hours). Reported: American Academy of Ophthalmology, Editor's Choice, 2025. AAO [UNVERIFIED — primary journal citation to be confirmed before publication]
Sunny S, et al. Hyperbaric oxygen therapy in CRAO (60 patients; 65% improved vision; mean 8.6 sessions). As reviewed in: Neuroprotection for Nonarteritic CRAO, J Clin Med. [UNVERIFIED — full citation to be confirmed before publication]
Butler FK, et al. CRAO pathophysiology and hyperbaric oxygen: the choroidal diffusion mechanism. As summarized in UHMS Indications, Ch. Arterial Insufficiencies.
Hadanny A, et al. Hyperbaric oxygen for CRAO (128-patient series; meaningful recovery; cherry-red spot and reversibility). As reviewed in: Neuroprotection for Nonarteritic CRAO. [UNVERIFIED — full citation to be confirmed before publication]
Beiran I, et al. Early hyperbaric oxygen therapy for retinal artery occlusion (treatment <8 hours). As cited in ALBalawi 2026 systematic review.
Varma DD, et al. Natural history and visual prognosis of central retinal artery occlusion (≈90% of untreated CRAO at 20/400 or worse). As cited in Lee et al., Scientific Reports, 2024.
ALBalawi HB, et al. Therapeutic efficacy of hyperbaric oxygen in central retinal artery occlusion: a systematic review and meta-analysis. J Clin Med. 2026;15(9):3530. MDPI
Rosignoli L, et al. Hyperbaric oxygen therapy for CRAO: a meta-analysis finding no significant benefit. 2021. As cited in [9]. [UNVERIFIED — full citation to be confirmed before publication]
Hong Kong e-Legislation. Pharmacy and Poisons Ordinance (Cap. 138). Cap. 138 on e-Legislation
