Hyperbaric oxygen therapy may rescue vision in central retinal artery occlusion (CRAO) when treatment begins within hours of vision loss. By dissolving enough oxygen into plasma to supply the inner retina from the choroidal circulation alone, HBOT keeps the retina alive while attempts are made to restore arterial flow. CRAO is a sub-presentation of UHMS condition #6 (Arterial Insufficiencies) and is recognised by Health Canada as one of the 14 conditions for which provincial health insurance covers HBOT at hospital-based programmes. Treatment is profoundly time-sensitive: the retinal cells begin to die within 90 to 100 minutes of complete arterial occlusion.
Quick Answer
Does HBOT help central retinal artery occlusion? Hyperbaric oxygen therapy may rescue vision in central retinal artery occlusion (CRAO) when treatment begins within hours of vision loss. By dissolving enough oxygen into plasma to supply the inner retina from the choroidal circulation alone, HBOT keeps the retina alive while attempts are made to restore arterial flow. CRAO is a sub-presentation of UHMS condition #6 (Arterial Insufficiencies) and is recognised by Health Canada as one of the 14 conditions for which provincial health insurance covers HBOT at hospital-based programmes. Treatment is profoundly time-sensitive: the retinal cells begin to die within 90 to 100 minutes of complete arterial occlusion.
Central retinal artery occlusion (CRAO) is the ophthalmic equivalent of a stroke: sudden, painless, severe vision loss in one eye caused by interruption of blood flow through the central retinal artery (an end-artery branch of the ophthalmic artery that supplies the inner retinal layers). Patients typically describe "a curtain coming down" or complete blackout in one eye, with vision typically reduced to counting fingers or worse on initial examination. The classic fundoscopic findings (retinal pallor with a characteristic cherry-red spot at the macula, where the underlying choroidal circulation shows through the otherwise pale retina) appear within minutes to hours of the occlusion.
CRAO is a recognised acute neuro-ophthalmic emergency. It affects approximately 1 to 2 per 100,000 people per year, with peak incidence in the seventh decade. Most cases are caused by embolic events, often from carotid atherosclerotic disease, atrial fibrillation, or rarely from cardiac sources (including endocarditis). Other mechanisms include giant cell arteritis (which is the indication for emergency high-dose corticosteroids if suspected), in-situ thrombosis on a stenotic vessel, vasospasm, and external compression from orbital pathology. Patients with CRAO have a substantially elevated short-term and long-term risk of cerebrovascular events; up to 25 percent will have a stroke or TIA within the next year, and the diagnosis triggers an urgent stroke-equivalent work-up in modern protocols.
The time-sensitivity of treatment is profound. Animal models demonstrate that retinal cells begin to die within 90 to 100 minutes of complete arterial occlusion, with progressive and largely irreversible damage by approximately 240 minutes. The practical implication is that any therapy with a chance of preserving vision must be delivered within hours, not days, of symptom onset. This time-pressure makes CRAO a hyperbaric emergency in the same operational tier as decompression sickness and arterial gas embolism.
Hyperbaric oxygen therapy treats CRAO by exploiting a unique anatomical feature of the retina: dual blood supply. The inner retina (the layers containing the ganglion cells, the neural elements responsible for vision) is supplied by the central retinal artery, which is occluded in CRAO. The outer retina (the photoreceptors and the retinal pigment epithelium) is supplied by the underlying choroidal circulation, which remains intact even when the central retinal artery is completely occluded. The distance between the choroid and the inner retina is small (the full thickness of the retina is approximately 250 microns), and at normobaric oxygen the choroidal circulation cannot deliver enough oxygen across this distance to keep the inner retina alive when the central retinal artery is blocked.
Inside a hyperbaric chamber at 2.4 to 2.8 ATA on 100 percent oxygen, plasma oxygen content rises 10- to 15-fold, raising choroidal pO2 to several hundred mmHg. At these tensions, dissolved oxygen can diffuse from the choroid across the full thickness of the retina, supplying the inner retinal layers from below even with the central retinal artery completely occluded. This essentially keeps the retina alive while attempts are made to restore arterial flow.
The second mechanism is restoration of perfusion through bubble-shrinkage in the rare CRAO cases caused by gas embolism (after diving accident, neck or thoracic surgery, or central-line placement). HBOT recompresses the bubble, restores arterial flow, and accelerates nitrogen washout. This mechanism does not apply to the more common embolic and thrombotic CRAO cases.
The third mechanism is anti-inflammatory and anti-reperfusion-injury. Once arterial flow is restored (whether spontaneously, with anterior-chamber paracentesis, with intra-arterial thrombolysis, or with HBOT-supported recovery), the resulting reperfusion can extend ischaemic injury through reactive oxygen species and neutrophil-mediated inflammation. HBOT blocks neutrophil adhesion to retinal endothelium, reduces lipid peroxidation, and supports endogenous antioxidant systems, limiting the secondary injury.
Typical Treatment Protocol
There is no single universally adopted protocol for CRAO; the most widely used Canadian and US regimens follow one of two patterns. The first is the standard recompression approach using US Navy Treatment Table 6 (recompression to 2.8 ATA on 100 percent oxygen for 75 minutes followed by stepwise decompression with intermittent air-breaks; total approximately 285 minutes), used for the initial session, followed by daily sessions at 2.4 to 2.5 ATA on 100 percent oxygen for 90 minutes for the next 7 to 14 days. The second is a single-session protocol at 2.4 to 2.5 ATA for 90 minutes daily from the outset, typically delivered for 5 to 14 days. The first session must begin as quickly as possible after the diagnosis is established. Most Canadian programmes will accept CRAO as an emergency and aim to start the first session within hours of onset. Other components of CRAO management (anterior-chamber paracentesis to mechanically reduce intraocular pressure and dislodge an embolus, ocular massage to promote movement of an embolus, sublingual nitrate or carbogen breathing to dilate retinal vessels, intra-arterial thrombolysis at specialised stroke centres) may be combined with HBOT as part of a multi-pronged approach. The decision is made jointly by ophthalmology, neurology, and hyperbaric medicine.
Level B - Moderate Evidence
Supported by controlled studies and clinical evidence
Animal models demonstrate that retinal cells begin to die within 90 to 100 minutes of complete central retinal artery occlusion, with progressive and largely irreversible damage by approximately 240 minutes. This time-sensitivity is the foundation of CRAO treatment urgency.
The retina has dual blood supply: the inner retinal layers from the central retinal artery (occluded in CRAO) and the outer retinal layers from the choroidal circulation (intact in CRAO). HBOT exploits this anatomy by raising choroidal pO2 enough to supply the inner retina from below across the full thickness of the retina.
Several case series and observational cohorts (Hadanny 2017, Menzel-Severing 2012, Murphy-Lavoie and others) suggest improved visual outcomes when HBOT is started within the first 6 to 8 hours of symptom onset, with diminishing but still meaningful benefit through 24 hours. Randomised trials are limited and ethically constrained by the rarity and time-sensitivity of the condition.
CRAO carries a substantially elevated short-term cerebrovascular risk: up to 25 percent of patients will have a stroke or TIA in the year following the event. Stroke work-up (carotid imaging, echocardiography, cardiac monitoring, ESR if giant cell arteritis suspected) is completed in parallel with HBOT and forms an essential part of CRAO management.
Standard adjunctive protocol is either US Navy Treatment Table 6 for the initial session followed by daily sessions at 2.4 to 2.5 ATA on 100 percent oxygen for 90 minutes for 7 to 14 days, or a single-session protocol at 2.4 to 2.5 ATA from the outset for 5 to 14 days. The first session must begin as quickly as possible after diagnosis.
Other components of CRAO management (anterior-chamber paracentesis, ocular massage, sublingual nitrate or carbogen breathing, intra-arterial thrombolysis at specialised stroke centres) may be combined with HBOT as part of a multi-pronged approach. The decision is made jointly by ophthalmology, neurology, and hyperbaric medicine.
Highest-evidence-tier studies tagged to this condition in the Canada Hyperbarics research database, ranked by evidence tier (1 = meta-analysis or RCT, 2 = cohort, 3 = case series), most recent first.
Korean J Ophthalmol · 2022 · Meta-Analysis
Clin Ophthalmol · 2021 · Clinical Guideline
Undersea Hyperb Med · 2018 · Clinical Study
Cureus · 2026 · Case Report
Studies in our database that include a ClinicalTrials.gov registration. Trial registration is a marker of methodological rigour because the protocol, primary outcome, and analysis plan are deposited before enrolment begins.
The British journal of ophthalmology · 2024 · Prospective Study · PMID 37722767
Sudden painless vision loss in one eye is a neuro-ophthalmic emergency. Patients should call 911 or go directly to the nearest emergency department; vision-saving treatment depends on the time elapsed since onset. The receiving emergency department arranges immediate ophthalmology assessment (typically by phone or telemedicine to the on-call ophthalmologist), basic stroke work-up (ECG, CBC, lipids, glucose, ESR if giant cell arteritis is suspected), and contacts the nearest hospital hyperbaric programme.
For CRAO of less than 24 hours' duration, most Canadian programmes will accept the patient as a hyperbaric emergency and aim to start the first session within hours. The first session is typically US Navy Treatment Table 6 (2.8 ATA on 100 percent oxygen for 75 minutes with stepwise decompression, total approximately 285 minutes) or a 90-minute session at 2.4 to 2.5 ATA. Multiplace chambers accommodate the longer Table 6 protocol; monoplace chambers are used for the shorter daily-session protocol.
After the initial session, daily sessions at 2.4 to 2.5 ATA on 100 percent oxygen for 90 minutes are typically delivered for the next 7 to 14 days. Some programmes deliver twice-daily sessions for the first 24 to 48 hours. Visual acuity, fundoscopy, and (where available) optical coherence tomography are repeated at intervals to track recovery. Stroke work-up (carotid imaging, echocardiography, cardiac monitoring) is completed in parallel because of the substantially elevated short-term cerebrovascular risk after CRAO. The ophthalmology team coordinates ongoing care with neurology, internal medicine, and hyperbaric medicine.
Central retinal artery occlusion is a sub-presentation of the Health Canada-recognised UHMS condition #6 (Arterial Insufficiencies), which also encompasses Enhancement of Healing in Selected Problem Wounds. CRAO is covered as an emergency hyperbaric indication at the 11 hospital-based hyperbaric programmes across seven provinces under provincial health insurance.
In Ontario, OHIP covers treatment at the three hospital programmes (Toronto General / UHN, Hamilton General Hospital, The Ottawa Hospital). Toronto General has particularly close working relationships with the major teaching-hospital ophthalmology services. CritiCall Ontario at 1-800-668-4357 is the standard line for inter-facility transfer when the patient is at a community hospital without an in-house chamber. In British Columbia, treatment is at Vancouver General Hospital with BC Ambulance critical-care transport. In Alberta, both Misericordia Edmonton (Covenant Health) and the Foothills Medical Centre / AJECCC Calgary (Alberta Health Services) accept CRAO referrals, with the Alberta hospital billing code 13.99I (per 15 minutes). RAMQ covers treatment at Hôpital du Sacré-Cœur de Montréal and Hôtel-Dieu de Lévis in Quebec. MSI (Nova Scotia), MCP (Newfoundland and Labrador), and Saskatchewan also cover their respective hospital programmes.
The practical limitation for CRAO is the time-sensitivity. Patients who present at community hospitals without an in-house chamber face a window-of-opportunity decision: transfer to a hyperbaric programme that may take hours, against the rapidly closing biological window. Most Canadian programmes will accept CRAO as a hyperbaric emergency for up to 24 hours after symptom onset, with the strongest signal of benefit in patients treated within the first 6 to 8 hours.
Hyperbaric oxygen therapy for the 14 Health Canada-recognised conditions, including Central Retinal Artery Occlusion, is delivered at the 11 hospital hyperbaric programmes located in seven provinces (Ontario, Quebec, British Columbia, Alberta, Nova Scotia, Newfoundland and Labrador, and Saskatchewan). The six provinces and territories without an in-province hospital programme (Manitoba, New Brunswick, Prince Edward Island, Yukon, Northwest Territories, and Nunavut) route patients to the nearest receiving hospital programme. Use the links below for province-specific coverage, referral pathway, and emergency routing details.
Hospital + Private
OHIP (Ontario Health Insurance Plan)
Hospital Only
MSP (Medical Services Plan)
Hospital + Private
Alberta Health / AHCIP
Hospital Only
RAMQ
Disrupted
Saskatchewan Health Authority
No Hospital Chamber
Manitoba Health
Hospital Only
MSI (Medical Services Insurance)
No Hospital Chamber
Medicare NB
Hospital Only
MCP (Medical Care Plan)
Out-of-Province Referral
Health PEI
Out-of-Province Referral
Yukon Health and Social Services
Out-of-Province Referral
NWT Health and Social Services
Out-of-Province Referral
Nunavut Department of Health
For acute or emergency presentations of Central Retinal Artery Occlusion, call 911 first. The receiving emergency department coordinates urgent transfer to the nearest hospital hyperbaric programme through the relevant provincial transfer network (CritiCall Ontario at 1-800-668-4357, BC Patient Transfer Network, EHS Nova Scotia, or equivalent). For diving-related emergencies, the Divers Alert Network (DAN) emergency hotline is 1-919-684-9111.
Untreated pneumothorax is the only absolute contraindication, because trapped intrathoracic air expands on decompression. Concurrent treatment with bleomycin or disulfiram are formally contraindicated but rarely encountered in this acute setting. Relative contraindications including severe chronic obstructive pulmonary disease with bullous lung disease, uncontrolled seizure disorder, and uncontrolled hypertension are weighed against the high risk of permanent vision loss without treatment, and treatment generally proceeds. Giant cell arteritis is not a contraindication to HBOT but it must be recognised early because it requires emergency high-dose corticosteroids regardless of HBOT decisions.
Central retinal artery occlusion (CRAO) is sudden, painless, severe vision loss in one eye caused by interruption of blood flow through the central retinal artery, which supplies the inner retinal layers. It is the ophthalmic equivalent of a stroke. Most cases are caused by embolic events from carotid disease, atrial fibrillation, or cardiac sources. Treatment is profoundly time-sensitive because retinal cells begin to die within 90 to 100 minutes of complete occlusion.
As quickly as possible, ideally within the first 6 to 8 hours of symptom onset, with diminishing but still meaningful benefit through 24 hours. Sudden painless vision loss in one eye should be treated as a neuro-ophthalmic emergency: call 911 or go directly to the nearest emergency department. The receiving department arranges immediate ophthalmology assessment and contacts the nearest hospital hyperbaric programme.
The retina has dual blood supply: the inner retinal layers from the central retinal artery (occluded in CRAO) and the outer retinal layers from the choroidal circulation (intact in CRAO). At hyperbaric pressures of 2.4 to 2.8 ATA on 100 percent oxygen, dissolved oxygen content in plasma rises enough that the choroidal circulation can supply the inner retinal layers from below, across the full thickness of the retina. This essentially keeps the retina alive while attempts are made to restore arterial flow.
Yes. CRAO is a sub-presentation of the Health Canada-recognised UHMS condition #6 (Arterial Insufficiencies) and is covered as an emergency indication at all 11 hospital-based hyperbaric programmes under OHIP, MSP, AHCIP, RAMQ, MSI, MCP, and Saskatchewan Health. The practical limitation is geographic and time-related: patients at community hospitals without an in-house chamber face a window-of-opportunity decision about transfer.
Several case series and observational cohorts report improved visual outcomes when HBOT is started within the first 6 to 8 hours of symptom onset. The evidence base is observational and ethically constrained by the rarity and time-sensitivity of CRAO; randomised trials are limited. The combination of HBOT with other CRAO measures (anterior-chamber paracentesis, ocular massage, intra-arterial thrombolysis at specialised centres) is the current standard multi-pronged approach.
In some cases, yes; in many cases, partially. Outcome depends primarily on time from onset to first treatment, the completeness of the original occlusion, and the underlying cause. Patients treated within the first 6 to 8 hours have the highest probability of meaningful visual recovery. Patients with cilioretinal artery sparing (a normal anatomical variant where part of the macula is supplied separately) generally have better outcomes regardless of treatment.
Typical course is 7 to 14 sessions. The first session is most often US Navy Treatment Table 6 (2.8 ATA on 100 percent oxygen for 75 minutes with stepwise decompression, total approximately 285 minutes) or a 90-minute session at 2.4 to 2.5 ATA. Daily sessions at 2.4 to 2.5 ATA on 100 percent oxygen for 90 minutes follow for the next 7 to 14 days. Some programmes deliver twice-daily sessions for the first 24 to 48 hours.
CRAO management is multi-pronged. Common other measures include anterior-chamber paracentesis (to mechanically reduce intraocular pressure and dislodge an embolus), ocular massage (to promote movement of an embolus along the artery), sublingual nitrate or carbogen breathing (to dilate retinal vessels), and intra-arterial thrombolysis at specialised stroke centres (for highly selected cases). High-dose corticosteroids are added if giant cell arteritis is suspected. Stroke work-up runs in parallel because of the elevated cerebrovascular risk.
CRAO carries a substantially elevated short-term cerebrovascular risk: up to 25 percent of patients will have a stroke or TIA in the year following the event. The same disease process (embolism from carotid disease, atrial fibrillation, or cardiac sources) that caused the retinal artery occlusion can cause a cerebral artery occlusion next. Stroke work-up includes carotid imaging (Doppler ultrasound, CT angiography, or MRA), echocardiography (to look for cardiac sources of embolism), cardiac rhythm monitoring (to detect atrial fibrillation), and ESR (to screen for giant cell arteritis). Initiation of secondary stroke prevention (antiplatelet therapy, anticoagulation if indicated, statin, blood-pressure control) is part of the standard CRAO management plan.
All 11 Canadian hospital hyperbaric programmes accept CRAO as an emergency indication. The Canada Hyperbarics verified directory at canadahyperbarics.ca/facilities/ lists all programmes with phone numbers, addresses, and current operational status. In an emergency, the local emergency department or ophthalmology team will arrange the referral; in Ontario, urgent inter-facility transfer is coordinated through CritiCall Ontario at 1-800-668-4357.