Emergency Medicine Resident and MedED Enthusiast. Learning and teaching medicine one doodle at a time!
The Pre-brief
Central retinal artery occlusion (CRAO) is an uncommon (2/100,000 cases per year in the U.S.) but often permanently disabling condition defined by interruption of blood supply to the retina. Patients present with painless vision loss. While it is not classically a condition which lands patients in the ICU, some facilities have begun using alteplase (tPA) for this “eye stroke”, leading patients to require ICU monitoring. Treatment options are limited, vision loss is typically severe, and prognosis is accordingly poor. Given a growing body of literature, CRAO is the most recent addition to the list of approved indications for hyperbaric oxygen therapy (HBOT) as outlined by the Undersea and Hyperbaric Medical Society. While inter-facility management of CRAO patients is currently extremely variable, tPA or HBOT (or both) can be considered if appropriate resources are available.
Background and Anatomy
In a recent scientific statement by the American Heart Association, ‘retinal infarct,’ as can occur in CRAO, is included in the definition of ‘ischemic stroke’. Occlusion of the central retinal artery can be secondary to thrombosis, embolus (most common), arteritis, vasospasm, or foreign material such as embolized dermal filler.
The central retinal artery enters the eye with the optic nerve and supplies tissue of the inner layers of the retina. It is a branch of the ophthalmic artery which stems from the internal carotid artery. On clinical and fundoscopic exam, patients with CRAO will typically have a relative afferent pupillary defect, a pale appearing retina, and a classic cherry red spot can be seen in the macula. Fundoscopic exam and emergent ophthalmology consultation are prudent to exclude alternative diagnoses such as vitreous hemorrhage or detachment. With the ever-growing presence of telemedicine, it is not unreasonable to ask for remote ophthalmology evaluation of retinal imaging if this technology is available to the emergency department provider but emergent, in-person consultation is not.
Major risk factors for CRAO include giant cell arteritis, atherosclerosis, and thromboembolic disease. Advanced age is also a risk factor as there is a fivefold increase in incidence in patients over the age of 80. It is also important to note that pathophysiologically, CRAO is akin to transient ischemic attack in that both can be signs of impending major cerebrovascular accident and warrant further neurologic and cardiovascular evaluation. High grade ipsilateral carotid artery stenosis is commonly found on subsequent workups in CRAO patients.
An important anatomical consideration is that 15-30% of the population also has a cilioretinal artery which is a part of the ciliary arterial supply. This branch, when present, supplies the retina in the region of the macula. In patients with this anatomical variant, central vision can be spared even in the event of CRAO. In patients with CRAO without a cilioretinal artery, 80% have a long term visual acuity of finger counting or worse.
Care for CRAO patients varies vastly from facility to facility, but generally should include ophthalmology and neurology evaluations. Given that blindness is a potential and common outcome, these patients should be triaged emergently in order to mobilize resources and consultants and to obtain timely neuroimaging. It is not unreasonable for CRAO presentations to activate ‘stroke alert’ pathways as it is, after all, a stroke of the eye.
Treatment Options
Treatment options are incredibly limited to the extent that the American Academy of Ophthalmology CRAO guideline states the following:
“In general, there are no proven treatments to reverse the vision loss caused by CRAO, BRAO, or OAO.”
(Where BRAO, OAO=branch retinal artery occlusion and ophthalmic artery occlusion respectively)
The classic teaching and consideration for interventions such as anterior chamber paracentesis or ocular massage have no legitimate supportive literature.
Steroids are indicated in arteritic causes of CRAO, and most commonly this occurs in the setting of giant cell arteritis. Of note, tPA and HBOT as discussed below have not been studied as treatments for arteritic CRAO (~5% of CRAOs).
tPA
Similar to the thoroughly protocolized algorithm for other types of ischemic stroke, multiple meta-analyses of observational studies demonstrate an improved recovery rate in vision when tPA is administered within 4.5 hours of symptom onset. There are currently three ongoing randomized controlled trials comparing IV tPA to placebo in CRAO patients. Dosing for intravenous tPA for CRAO is done in 15mg aliquots with interval reassessments of fundoscopy and visual acuity until vision is restored or a dose of 50mg is reached. Analogous to catheter-directed therapy in certain pulmonary embolism patients, micro-catheterization of the ophthalmic artery with catheter directed thrombolysis is being explored in some centers.
HBOT and Rationale
Being one of the most metabolically active tissues in the body, the retina does not tolerate ischemia well. While the ischemia and subsequent necrosis downstream from a CRAO is what leads to vision loss, the retina does have an exploitable feature in that it is an extremely thin tissue (200-300μm). As such, diffusion of oxygen from choroidal circulation supplemented with increased pO2 can theoretically maintain retinal tissue and visual acuity. Enter HBOT. HBOT can be considered as a temporizing measure to maintain oxygenation of the retina while revascularization is otherwise pursued via other intervention or natural course (natural recanalization is typically within 72hr).
Animal studies have demonstrated that diffusion from choroidal circulation is sufficient to supply >95% of retinal needs in hyperbaric conditions. Numerous case series and retrospective case-control studies suggest improved visual acuity outcomes in CRAO patients treated with HBOT and collectively indicate better outcomes with reduction in time interval from vision loss to HBOT initiation.
Other Considerations
- HBOT or tPA need to be started as soon as possible as there is a certain point in ischemic retinal injury beyond which tissue is no longer salvageable. If presenting within 24h, HBOT can be considered. Perhaps an overused cliché in medicine but literal in this case: “Time is tissue”.
- Occlusions may occur more proximal in the ophthalmic artery such that flow to both the choroidal blood supply and the central retinal artery ceases. In this case, there is no hope for choroidal diffusion supplying oxygen to the retina, even with HBOT.
- Depending on the degree and location of occlusion, supplemental (non-hyperbaric) oxygen can sometimes be adequate to improve retinal survival via oxygen diffusion as discussed above. This should be trialed immediately in suspected CRAO as availability is ubiquitous relative to that of HBOT. However, in cases failing sea-level supplemental oxygen, escalation to HBOT should be pursued where available.
tPA plus HBOT offers an intriguing combination therapy for CRAO which is currently under further study.
The Debrief
- CRAO is the equivalent of a stroke of the eye. Stroke alert activation is therefore appropriate at presentation to expedite ophthalmology and neurology evaluations as well as neuroimaging.
- While rare, CRAOs typically have poor outcomes, with 80% of patients without the cilioretinal arterial variant having long term visual acuity of finger counting or less.
- Risk factors are similar to those of other strokes and include atherosclerosis and advanced age among other general cardiovascular risk factors.
- Treatment options are limited. tPA and HBOT can both be considered as treatment options for CRAO. Further studies will be useful for each independently as well as for both in combination as treatments for CRAO.
References
Dollery CT, Bulpitt CJ, Kohner EM. Oxygen supply to the retina from the retinal and choroidal circulations at normal and increased arterial oxygen tensions. Invest Ophthalmol. 1969;8:588–594.
Mac Grory B, Nackenoff A, Poli S, Spitzer MS, Nedelmann M, Guillon B, Preterre C, Chen CS, Lee AW, Yaghi S, et al. Intravenous fibrinolysis for central retinal artery occlusion: a cohort study and updated patientlevel meta-analysis. Stroke. 2020;51:2018–2025. doi: 10.1161/STROKEAHA.119.028743.
Mac Grory, B., Schrag, M., Biousse, V., Furie, K., Gerhard-Herman, M., Lavin, P., Sobrin, L., Tjoumakaris, S., Weyand, C., & Yaghi, S. (2021). Management of central retinal artery occlusion. AHA Scientific Statement, 52(00). https://doi.org/10.1161/STR.0000000000000366.
Murphy-Lavoie, H., Butler, F., & Hagan, C. (2019). Arterial Insufficiencies: Central Retinal Artery Occlusion. In R. Moon (Ed.), Undersea and Hyperbaric Medical Society Hyperbaric Oxygen Therapy Indications (14th ed., pp. 15–30). essay, Best Publishing Company.
