Central Retinal Artery Occlusion (CRAO) Eye Stroke: Sudden Painless Monocular Blindness, Cherry-Red Spot, and 90-Minute Hyperbaric or tPA Window¶

Sudden, completely painless loss of vision in one eye occurring over seconds, often described as a dark window shade pulling down or a light switch turning off, is the hallmark of central retinal artery occlusion (CRAO), medically classified as an acute ischemic eye stroke. Call your local emergency number (911 in the United States and Canada, 112 across the European Union, 999 in the United Kingdom) or consult our emergency numbers immediately and demand emergency ambulance transport directly to a Designated Stroke Center Hospital. While waiting for paramedics, evaluate the patient for concurrent cerebral stroke or transient ischemic attack (TIA), screen older adults for arteritic causes using our giant cell arteritis and temporal arteritis guide, and compare painful red-eye emergencies in our acute angle-closure glaucoma guide.

Because the retina is embryologically and anatomically an outpouching of the brain's diencephalon supplied by the central retinal artery (a branch of the ophthalmic artery, which is the very first intracranial branch of the internal carotid artery), the American Heart Association (AHA) and American Stroke Association (ASA) define acute retinal arterial ischemia as a central nervous system infarction equivalent to a cerebral stroke. Experimental and clinical human studies demonstrate that complete occlusion of the central retinal artery triggers irreversible death of the inner retinal ganglion cells beginning at 90 to 100 minutes, with massive or total retinal infarction completed by 240 minutes (4 hours). In addition, brain diffusion-weighted magnetic resonance imaging (DWI-MRI) reveals that 15 to 25 percent of patients presenting with acute CRAO have simultaneous, often silent acute ischemic brain infarctions from the exact same carotid artery plaque or cardiac embolus. Routing a patient with painless monocular blindness to a retail optometrist or waiting until the next morning forfeits both the 4.5-hour intravenous thrombolysis window (alteplase or tenecteplase) and the early hyperbaric oxygen therapy (HBOT) rescue window while leaving the patient exposed to a fatal hemispheric stroke.

Do this now¶

1. Cover one eye at a time to confirm monocular vision loss, verify that the eye is PAINLESS, and record the exact minute symptoms started ("Last Known Well" time). Have the person cover their right eye with their palm, then cover their left eye. If vision is blacked out, reduced to counting fingers or seeing only hand motions, or missing an upper or lower half in one eye without eye pain, treat it immediately as an eye stroke. Write down the exact clock minute the vision changed, as stroke teams require this timestamp to authorize intravenous clot-busting medication.
2. Call 911 / 112 / 999 immediately and request transport to a Designated Stroke Center, NOT an optometrist, urgent care clinic, or stand-alone eye clinic. Tell the dispatcher clearly: "The patient has sudden, painless blindness in one eye that started at [Time]. We suspect an acute Central Retinal Artery Occlusion, which is an eye stroke, and need a Stroke Code ambulance to a hospital with intravenous tPA and stroke neurology capabilities."
3. Lay the person completely flat on their back (supine) with their head at zero degrees elevation. Unlike congestive heart failure or traumatic brain injury where the head is elevated, lying a patient with acute CRAO completely flat maximizes mean arterial pressure and gravitational hydrostatic perfusion pressure through the ophthalmic artery and residual cilioretinal or pial collateral vessels feeding the starving retina.
4. Even if the dark curtain lifts and vision returns to 100 percent normal after 2 to 15 minutes (Amaurosis Fugax), still go to the Stroke Center by ambulance immediately. Temporary painless monocular blindness (amaurosis fugax, or "fleeting blindness") is a retinal transient ischemic attack (TIA) caused by a cholesterol crystal (Hollenhorst plaque) or platelet-fibrin clot briefly plugging the retinal artery before breaking up. The highest risk of a permanent blinding CRAO or a massive middle cerebral artery brain stroke occurs within the first 24 to 72 hours after an episode of amaurosis fugax.
5. Screen every patient aged 50 or older immediately for Giant Cell Arteritis (Temporal Arteritis) red flags. Ask specifically about new temple headache, scalp tenderness when combing hair, jaw pain or fatigue while chewing food (jaw claudication), double vision, fever, or shoulder/hip stiffness. In 5 to 10 percent of CRAO cases (arteritic CRAO), the artery is blocked by autoimmune vasculitis rather than a clot; without immediate high-dose intravenous steroids, the second eye can go permanently blind within hours to days.
6. Keep the patient Nothing by Mouth (NPO), never take home aspirin before a hospital brain scan, and avoid aggressive bystander eyeball compression. Do not give food, drink, or oral blood thinners/aspirin at home, because hospital stroke protocols require a quick non-contrast head CT scan first to rule out intracranial hemorrhage before giving intravenous thrombolytics (alteplase/tenecteplase) or dual antiplatelet therapy. Do not press forcefully on the eyeball, which can rupture an eye with prior surgery or dislodge clots unpredictably.

Clinical decision tree for sudden painless monocular vision loss¶

Use this emergency triage flowchart to distinguish thromboembolic CRAO, branch retinal artery occlusion (BRAO), transient amaurosis fugax, and arteritic CRAO, and activate the proper hospital pathway.

flowchart TD
    Start["Sudden Painless Loss of Vision in ONE Eye<br/>(Blackout, Counting Fingers, or Horizontal Curtain)<br/>Confirmed by Covering Each Eye Separately"] --> DurationCheck{"Did Vision Return to Normal<br/>Within 2 to 15 Minutes,<br/>or Is Vision Still Lost?"}

    DurationCheck -->|"Vision Returned Completely<br/>After 2 to 15 Minutes<br/>('Shade Pulled Down Then Lifted')"| Amaurosis["AMAUROSIS FUGAX (RETINAL TIA):<br/>1. Call 911 / 112 / 999 Immediately for Stroke Center<br/>2. Extreme 24 to 72 Hour Risk of Brain Stroke or CRAO<br/>3. Urgent CTA Head/Neck (Check >70% Carotid Stenosis),<br/>   Brain DWI-MRI, ECG/Telemetry, and Dual Antiplatelets"]

    DurationCheck -->|"Vision Remains Dark or Missing<br/>(Persistent Occlusion)"| AgeGCA{"Is Patient Age >= 50 Years WITH<br/>Temple Headache, Jaw Claudication,<br/>Scalp Tenderness, or PMR Stiffness?"}

    AgeGCA -->|"YES: Suspect Arteritic CRAO<br/>(5% to 10% of All CRAO Cases)"| ArteriticCRAO["ARTERITIC CRAO (GIANT CELL ARTERITIS):<br/>1. Immediate High-Dose IV Methylprednisolone<br/>   (500 to 1,000 mg IV Daily) BEFORE Temporal Biopsy<br/>2. Protects the Fellow Eye and Prevents<br/>   Contralateral Blindness Within 24 Hours to 7 Days<br/>3. Stat ESR, CRP, Platelets + Ophthalmology Consult"]

    AgeGCA -->|"NO: Suspect Non-Arteritic<br/>Thromboembolic CRAO or BRAO<br/>(90% to 95% of Cases)"| TimeWindow{"What Is the Time Elapsed Since<br/>Symptom Onset ('Last Known Well')?"}

    TimeWindow -->|"<= 4.5 Hours<br/>(Especially Within 90 to 180 Minutes)"| HyperacuteCRAO["HYPERACUTE STROKE CODE PATHWAY:<br/>1. Lay Patient Flat on Back (0 Degrees Supine)<br/>2. Stat Non-Contrast Head CT (Rule Out Bleed)<br/>3. Consider IV Alteplase or Tenecteplase (<= 4.5 hrs)<br/>   Per AHA/ASA CRAO Stroke Center Protocol<br/>4. Immediate Hyperbaric Oxygen (HBOT at 2.0 to 2.8 ATA)<br/>   if Available + IOP Reduction to Dislodge Embolus"]

    TimeWindow -->|"> 4.5 Hours to 24 Hours"| SubacuteCRAO["EARLY SUBACUTE RESCUE & STROKE WORKUP:<br/>1. Emergent Hyperbaric Oxygen Therapy (HBOT)<br/>   Window Up to 12 to 24 Hours (Choroidal Diffusion)<br/>2. Medical IOP Lowering (IV Acetazolamide + Drops)<br/>3. Inpatient Stroke Admission: Brain DWI-MRI,<br/>   Carotid CTA/Ultrasound, Echocardiogram, Telemetry"]

Pathophysiology: Dual retinal blood supply, the cherry-red spot, and the 90-minute ischemic clock¶

To understand why central retinal artery occlusion causes such profound, instantaneous blindness, why fundoscopy reveals a "cherry-red spot," and why hyperbaric oxygen can keep the retina alive even while the central retinal artery is blocked, one must examine the unique dual vascular anatomy of the human retina.

1. The dual circulation of the retina: Central retinal artery vs. choroidal choriocapillaris¶

The human retina is composed of ten microscopic histological layers that are nourished by two completely separate arterial beds (both branching off the ophthalmic artery, which arises from the supraclinoid internal carotid artery):

• Inner Retinal Layers (Supplied by the Central Retinal Artery): The central retinal artery (CRA) pierces the underside of the optic nerve about 10 to 12 millimeters behind the eyeball, travels straight down the center of the optic nerve, and emerges at the optic disc, where it divides into four main branches (superior nasal, superior temporal, inferior nasal, and inferior temporal arterioles). These arterioles are true anatomical end-arteries with zero anastomoses between branches. They supply the inner two-thirds of the retina: the nerve fiber layer, the ganglion cell layer (whose axons form the optic nerve), the inner plexiform layer, and the inner nuclear layer.
• Outer Retinal Layers and Fovea (Supplied by the Choroidal Circulation via Posterior Ciliary Arteries): The outer one-third of the retina, consisting of the photoreceptor rods and cones and the retinal pigment epithelium (RPE), contains no blood vessels of its own. Instead, it receives all of its oxygen and nutrients by passive diffusion across Bruch's membrane from the underlying choriocapillaris, a dense vascular bed fed by the short and long posterior ciliary arteries.
• The Cilioretinal Artery Variant (The 15% to 25% Anatomical Lifesaver): In 15 to 25 percent of human eyes, a small accessory vessel called a cilioretinal artery branches off the posterior ciliary (choroidal) circulation at the temporal edge of the optic disc and supplies the papillomacular bundle and central fovea. If a patient with a patent cilioretinal artery suffers a complete blockage of their central retinal artery, their entire peripheral visual field goes pitch black, but a tiny central island of 20/20 reading vision remains miraculously intact because the posterior ciliary circulation is still flowing. (Conversely, in Giant Cell Arteritis where the posterior ciliary arteries are inflamed, both circulations fail simultaneously).

+-------------------------------------------------------------------------+
|         DUAL BLOOD SUPPLY OF THE RETINA & THE CHERRY-RED SPOT           |
+-------------------------------------------------------------------------+
|  INTERNAL CAROTID ARTERY ---> OPHTHALMIC ARTERY                         |
|                                      |                                  |
|         +----------------------------+----------------------------+     |
|         |                                                         |     |
|         v                                                         v     |
|  1. CENTRAL RETINAL ARTERY (CRA)           2. SHORT POSTERIOR CILIARY   |
|     * True end-artery (no collaterals)        ARTERIES (CHOROIDAL BED)  |
|     * Feeds INNER 2/3 of Retina:              * Feeds OUTER 1/3 Retina: |
|       - Nerve Fiber Layer                       - Photoreceptors (Rods  |
|       - Ganglion Cell Layer                       and Cones)            |
|       - Inner Plexiform & Nuclear Layers        - Retinal Pigment Epith.|
|     * Blocked in Thromboembolic CRAO          * Remains OPEN in Non-    |
|       -> Inner retina swells & turns            Arteritic CRAO          |
|          OPAQUE MILKY-WHITE                   * Foveola has NO inner    |
|                                                 layers -> Red choroid   |
|                                                 shines through as a     |
|                                                 "CHERRY-RED SPOT"       |
+-------------------------------------------------------------------------+

2. Why the "Cherry-Red Spot" and "Boxcarring" appear on retinal examination¶

When an embolus or thrombus plugs the central retinal artery (usually at its narrowest anatomical bottleneck where it pierces the lamina cribrosa of the optic nerve head or at the dural sheath entry): 1. Opaque Milky-White Inner Retinal Edema: Within 15 to 60 minutes of ischemia, intracellular ATP depletion causes failure of sodium-potassium pumps in the inner retinal ganglion cells and nerve fibers (cytotoxic edema). The normally transparent inner retina swells and turns cloudy, pale, and milky-white across the posterior pole. 2. The Foveal Cherry-Red Spot: At the exact center of the macula, in a tiny 0.35-millimeter pit called the foveola, the inner retinal layers (ganglion cells and nerve fibers) are anatomically pushed aside so light can strike the photoreceptors directly. Because there are no inner retinal layers at the foveola to turn milky-white, the healthy, blood-filled red choroid and retinal pigment epithelium underneath continue to shine brightly through the ultra-thin foveola, surrounded by a halo of stark white ischemic retina. This stark contrast creates the pathognomonic cherry-red spot on fundoscopy (present in up to 90 percent of CRAO eyes). 3. Arteriolar Attenuation and "Boxcarring" ("Cattle-Trucking"): Because arterial inflow has stopped, the retinal arterioles become thread-thin, and the stagnant red blood cell column inside both the arterioles and venules breaks up into dark red segments separated by clear plasma gaps that slowly inch forward and backward like disconnected freight train cars (boxcarring or cattle-trucking). 4. Visible Intra-Arterial Emboli: In 20 to 40 percent of cases, the examiner can see the actual culprit embolus lodged at an arterial bifurcation: - Cholesterol Embolus (Hollenhorst Plaque, 74% of visible emboli): Bright, glistening, golden-yellow or orange refractile crystals arising from ulcerated internal carotid artery or aortic arch atherosclerotic plaques. - Fibrin-Platelet Embolus (15.5% of emboli): Dull, grayish-white, elongated plugs that mold to the vessel wall, arising from mural thrombi in carotid stenosis or cardiac chambers (atrial fibrillation, post-myocardial infarction). - Calcific Embolus (10.5% of emboli): Chalky, solid white, non-refractile chunks arising from calcified aortic stenosis or mitral annular calcification; because they are rock-hard and lodge proximally, calcific emboli cause the most severe, permanent infarctions.

3. The 90-to-240-minute retinal tolerance window (Hayreh's research)¶

Experimental primate studies by Dr. Sohan Singh Hayreh established the exact ischemic survival clock of the inner retina: - 0 to 90 Minutes (Complete Recovery Window): If central retinal artery flow is restored within 90 to 97 minutes of complete occlusion, the inner retina recovers with zero permanent damage and full return of vision. - 90 to 240 Minutes (Partial Salvage Window): Between 97 and 240 minutes (1.5 to 4 hours), irreversible death of retinal ganglion cells escalates rapidly; however, because most human CRAO cases retain residual trickle or collateral flow, emergency thrombolysis or hyperbaric oxygen within 4.5 hours can still salvage meaningful vision. - Beyond 240 Minutes (4 Hours): Total or near-total infarction of the inner retina occurs, resulting in permanent optic atrophy and vision limited to counting fingers or hand motion in over 80 percent of untreated eyes.

Etiology: Non-arteritic (thromboembolic) vs. arteritic (Giant Cell Arteritis) CRAO¶

Every patient with acute CRAO or amaurosis fugax must be immediately classified into one of two etiologic categories because their emergency medical treatments are completely different:

Cosmetic facial filler injections: An iatrogenic cause of blinding CRAO¶

Clinicians and patients must also recognize an iatrogenic cause of catastrophic CRAO in young adults: accidental intra-arterial injection of cosmetic dermal fillers (hyaluronic acid, calcium hydroxylapatite, or autologous fat) into the glabellar (frown lines), nasal bridge, forehead, or nasolabial fold regions. - The facial angular artery, supratrochlear artery, and supraorbital artery are direct terminal branches of the ophthalmic artery. - If a needle pierces one of these facial arteries and injects filler under high pressure, the column of filler gel is pushed retrograde into the main ophthalmic artery inside the orbit. When plunger pressure is released, systolic blood pressure shoots the filler antegrade straight into the central retinal artery, posterior ciliary arteries, and middle cerebral artery. - Unlike a blood clot, filler occlusion causes excruciating immediate orbital pain and instantaneous No Light Perception (NLP) blindness on the injection table, often with ophthalmoplegia, ptosis, forehead skin livedo reticularis, and cerebral stroke. - Emergency Management: Stop the injection immediately, inject high-dose hyaluronidase (1,500+ units) into the site and supraorbital/supratrochlear notches (with specialist retrobulbar hyaluronidase), start hyperbaric oxygen, and call 911/112/999 for Stroke Center transport.

Bedside pupillary hallmark: The Relative Afferent Pupillary Defect (Marcus Gunn pupil)¶

Any paramedic or physician can confirm severe optic nerve or inner retinal ischemia in 10 seconds in a dim room using the Swinging Flashlight Test to detect a Relative Afferent Pupillary Defect (RAPD, or Marcus Gunn pupil):

1. Have the patient look at a distant target in a dim room and shine a penlight into the healthy eye for 3 seconds: both pupils constrict briskly (direct response in the healthy eye and consensual response in the blind CRAO eye).
2. Quickly swing the penlight across the nose into the affected (CRAO) eye: instead of staying constricted, both pupils immediately dilate right into the beam of the flashlight.
3. Why this happens: Because the infarcted inner retina sends almost zero electrical signal down the optic nerve to the midbrain, the brain perceives swinging the light to the blind eye as "turning the lights off," causing both pupils to dilate paradoxically. A marked RAPD appears within seconds of CRAO and rules out functional vision loss, corneal haze, or simple cataract.

Pre-hospital and Emergency Department rescue therapies: What works and what to avoid¶

1. Intravenous Thrombolysis (Alteplase or Tenecteplase within 4.5 hours)¶

In 2021, the American Heart Association (AHA) and American Stroke Association (ASA) published a landmark Scientific Statement (Management of Central Retinal Artery Occlusion) endorsing the treatment of acute non-arteritic CRAO within 4.5 hours of symptom onset using intravenous tissue plasminogen activator (IV alteplase \(0.9\text{ mg/kg}\), maximum \(90\text{ mg}\), with 10% given as a 1-minute bolus and 90% over 60 minutes, or IV tenecteplase) at designated Stroke Centers, provided the patient has disabling monocular vision loss and no contraindications on non-contrast head CT or clinical screening. - Clinical Efficacy: Meta-analyses of patient-level data demonstrate that while spontaneous visual recovery (to 20/100 or better) occurs in fewer than 15 to 17 percent of untreated CRAO patients, administering intravenous alteplase within 4.5 hours increases the rate of meaningful visual recovery to 35 to 50 percent, with the highest recovery rates achieved when thrombolysis is started within the first 90 to 180 minutes. - Why Intra-Arterial Thrombolysis (IAT) Requires Caution: While catheter-directed intra-arterial tPA directly into the ophthalmic artery can recanalize the vessel at specialized neurointerventional centers, the prospective randomized EAGLE trial was halted early because catheterization took longer to initiate (mean > 9 hours) and carried a higher risk of intracerebral hemorrhage without superior vision outcomes compared to conservative care at late timepoints. Intravenous thrombolysis remains the fastest, most accessible evidence-based reperfusion option within 4.5 hours.

2. Hyperbaric Oxygen Therapy (HBOT): Oxygenating the inner retina via the choroid¶

Hyperbaric Oxygen Therapy (HBOT) receives an American Heart Association Class IIb recommendation and a Level 1 indication from the Undersea and Hyperbaric Medical Society (UHMS) for acute CRAO because of a brilliant physiological bypass mechanism:

+-------------------------------------------------------------------------+
|       HOW HYPERBARIC OXYGEN (HBOT) BYPASSES A BLOCKED RETINAL ARTERY    |
+-------------------------------------------------------------------------+
|  UNDER NORMAL ROOM AIR (21% O2 AT 1.0 ATMOSPHERE ABSOLUTE):             |
|  * Choroidal blood (posterior ciliary arteries) only diffuses far       |
|    enough to supply the OUTER 1/3 of the retina (photoreceptors).       |
|  * The INNER 2/3 of the retina (ganglion cells) receives 0% oxygen      |
|    when the Central Retinal Artery is blocked -> Infarcts in 90 mins.   |
+-------------------------------------------------------------------------+
|  INSIDE A HYPERBARIC CHAMBER (100% O2 AT 2.0 TO 2.8 ATMOSPHERES):       |
|  * Arterial partial pressure of oxygen (PaO2) rockets from 100 mmHg     |
|    up to 1,400 to 2,000 mmHg dissolved directly in blood plasma.        |
|  * This massive oxygen gradient drives oxygen from the open CHOROIDAL   |
|    choriocapillaris straight across the entire thickness of the retina  |
|    to keep the INNER retinal ganglion cells alive while the central     |
|    retinal artery recanalizes (available up to 8 to 24 hours post-onset)|
+-------------------------------------------------------------------------+

• Under normal room air breathing (1 atmosphere absolute [ATA]), oxygen diffusing from the open choroidal choriocapillaris can only reach the outer one-third of the retina.
• When a patient is placed inside a hyperbaric oxygen chamber breathing 100% oxygen at 2.0 to 2.8 ATA (provided the posterior ciliary arteries are open, i.e., non-arteritic CRAO), the dissolved plasma oxygen partial pressure (\(\text{PaO}_2\)) rises nearly twenty-fold (above \(1,500\text{ mmHg}\)). This enormous diffusion gradient pushes oxygen from the choroid across the full thickness of the retina to fully oxygenate the starving inner retinal ganglion cells without needing a single red blood cell to pass through the blocked central retinal artery.
• If the patient's vision improves inside the hyperbaric chamber (confirming the retinal cells are stunned in the ischemic penumbra rather than dead), customized HBOT sessions and supplemental normobaric oxygen are continued until endogenous fibrinolysis reopens the central retinal artery.

3. Medical intraocular pressure reduction and why historical maneuvers are discouraged¶

To help blood pressure push a fragile cholesterol or platelet embolus further downstream into a smaller peripheral branch arteriole (converting a total CRAO into a smaller peripheral BRAO that spares central macular vision), emergency physicians often administer immediate intraocular pressure-lowering medications: - Intravenous Acetazolamide (500 mg IV) plus topical timolol 0.5% and brimonidine/apraclonidine drops lower intraocular pressure from 16 mmHg down toward 8 to 10 mmHg. Because retinal arterial perfusion pressure equals mean ophthalmic arterial pressure minus intraocular pressure (\(\text{RPP} = \text{MAP}_{\text{oph}} - \text{IOP}\)), dropping IOP immediately increases the net forward push behind the clot. - Why Untrained Ocular Massage, Anterior Chamber Paracentesis, and Paper-Bag Breathing Are Discouraged by AHA Guidelines: - Paper-bag rebreathing / Carbogen inhalation: Breathing into a paper bag to raise carbon dioxide (\(\text{PaCO}_2\)) and dilate retinal vessels risks inducing dangerous systemic hypoxia in elderly stroke patients and has shown no clinical benefit. - Forceful bystander eyeball massage: Untrained digital compression delays stroke transport, can rupture eyes with prior cataract/corneal surgery or subluxate lenses, and is no longer recommended outside specialist ophthalmology care. - Anterior chamber needle paracentesis and vasodilators (sublingual nitroglycerin/nifedipine): Sublingual nitroglycerin or nifedipine can drop systemic blood pressure, which dangerously reduces perfusion pressure to both the ischemic retina and any concurrent cerebral stroke penumbra.

Mandatory inpatient stroke workup: Why every CRAO patient needs brain MRI and carotid imaging¶

Even if a patient presents more than 24 hours after vision loss when the retina can no longer be rescued, acute CRAO or amaurosis fugax remains a life-threatening neurovascular emergency: 1. 25% Concurrent Acute Brain Stroke on DWI-MRI: One in four patients with acute CRAO or BRAO has acute ischemic infarcts on brain diffusion-weighted MRI, and most of those brain infarcts have zero obvious limb weakness at the moment of presentation. 2. Ipsilateral Carotid Artery Stenosis or Dissection: Computed tomography angiography (CTA), magnetic resonance angiography (MRA), or carotid duplex ultrasound reveals hemodynamically significant (\(\ge 50\%\) to \(70\%\)) internal carotid artery stenosis on the same side as the blind eye in up to 40 percent of patients. Urgent carotid endarterectomy (CEA) or carotid artery stenting within 14 days prevents a catastrophic hemispheric stroke. In patients under age 50 (especially after neck trauma, chiropractic manipulation, weightlifting, or coughing), CTA/MRA of the neck is required to rule out internal carotid artery dissection. 3. Cardioembolic and Systemic Evaluation: Every patient requires a 12-lead ECG and inpatient telemetry/ambulatory cardiac monitoring (to detect occult atrial fibrillation requiring oral anticoagulation), transthoracic or transesophageal echocardiography (for valvular vegetations, left ventricular thrombus, or patent foramen ovale), lipid panel, hemoglobin A1c, and immediate ESR, CRP, and complete blood count in all patients aged 50 and older to exclude Giant Cell Arteritis.

Exact communication script for 911 / 112 / 999 and hospital stroke triage¶

When calling emergency services or arriving at an emergency department triage desk, use this exact script so the patient triggers an immediate Hospital Code Stroke rather than waiting hours in a general waiting room:

"I need an emergency ambulance for a suspected Eye Stroke at [Exact Address]. The patient is a [Age]-year-old [male/female] who developed sudden, completely painless blindness in the [left/right] eye at exactly [Time: e.g., 10:15 AM], which was [Number] minutes ago. We suspect an acute Central Retinal Artery Occlusion (CRAO). Per American Heart Association Stroke Guidelines, we need immediate Code Stroke transport to a Designated Stroke Center Hospital within the 4.5-hour window for a stat head CT, stroke neurology evaluation for intravenous thrombolysis, and hyperbaric oxygen or ophthalmology evaluation. We have the patient lying completely flat on their back."

Frequently asked questions¶

Why is painless sudden blindness in one eye treated as an emergency brain stroke when my arms, legs, and speech feel completely normal?¶

The retina at the back of your eye is actually brain tissue, and the central retinal artery that feeds it branches directly off the ophthalmic and internal carotid arteries that supply the entire front half of your brain. When a blood clot or cholesterol plaque blocks the central retinal artery, retinal cells begin dying permanently within 90 minutes, and brain MRI scans show that 1 in 4 patients with an eye stroke simultaneously have silent blood clots lodged in their brain that can trigger a massive paralyzing stroke within hours or days.

What does a "cherry-red spot" in the back of the eye mean during a central retinal artery occlusion?¶

When the central retinal artery is blocked, the inner layers of the retina lose oxygen, swell with fluid, and turn milky-white and opaque across the back of the eye. However, the tiny center-point of your vision (the foveola) naturally has no inner retinal layers and is fed by a separate layer of blood vessels underneath called the choroid; because the red choroid stays open and shines brightly through the thin foveola surrounded by the milky-white swollen retina, doctors see a vivid "cherry-red spot" during an eye exam.

Why did the doctor tell me to lie completely flat on my back instead of sitting up in a chair?¶

When the main artery feeding your retina is blocked by a clot, every millimeter of mercury of blood pressure helps push oxygenated blood through tiny backup collateral vessels around the optic nerve. Lying completely flat on your back (at zero degrees) uses gravity to maximize arterial blood pressure to your head and eyes, whereas sitting upright drops arterial perfusion pressure in the eye and accelerates retinal cell death.

How can a hyperbaric oxygen chamber save vision if the central retinal artery is still blocked by a clot?¶

The back wall of your eye has a second blood supply called the choroid (fed by the posterior ciliary arteries) that normally only supplies oxygen to the outer one-third of the retina. Inside a hyperbaric oxygen chamber at 2 to 2.8 times normal atmospheric pressure, 15 to 20 times more pure oxygen dissolves directly into your blood plasma, creating a pressure gradient strong enough for oxygen from the open choroid to diffuse all the way across the retina and keep the starving inner retinal cells alive until your body's natural enzymes dissolve the clot.

Sources checked¶

• American Heart Association (AHA) and American Stroke Association (ASA, United States): Management of Central Retinal Artery Occlusion: A Scientific Statement From the American Heart Association (Mac Grory et al., Stroke, 2021, establishing acute CRAO as a medical stroke emergency, defining the \(\le 4.5\text{ hour}\) intravenous alteplase/tenecteplase pathway, supine positioning, hyperbaric oxygen Class IIb recommendation, and inpatient neurovascular workup).
• American Academy of Ophthalmology (AAO, United States): Preferred Practice Pattern (PPP) Guidelines: Retinal and Ophthalmic Artery Occlusions (Flaxel et al., detailing clinical triage of non-arteritic vs. arteritic CRAO, BRAO, and ophthalmic artery occlusion, cilioretinal artery sparing, and concurrent 15% to 25% DWI-MRI silent brain infarction rates).
• Undersea and Hyperbaric Medical Society (UHMS, United States): Hyperbaric Oxygen Therapy Indications: Central Retinal Artery Occlusion (2.0 to 2.8 ATA oxygen diffusion across Bruch's membrane from the choriocapillaris to salvage inner retinal ischemia within the early 8-to-24-hour window).
• National Institute for Health and Care Excellence (NICE, United Kingdom) and European Stroke Organisation (ESO): Guidelines on Intravenous Thrombolysis for Acute Ischaemic Stroke and Management of Transient Ischaemic Attack (Amaurosis Fugax) (urgent carotid imaging and <14-day carotid endarterectomy targets).

Related guides¶

• Sudden vision loss, retinal detachment, and acute angle-closure glaucoma overview
• Giant cell arteritis (temporal arteritis), jaw claudication, and saving the second eye
• Acute angle-closure glaucoma: halo vision, rock-hard eye, and why dark rooms worsen pupillary block
• Stroke recognition (FAST) and emergency response
• Transient ischemic attack (TIA) mini-stroke and 24-hour stroke risk