Central
retinal artery occlusion treated with oxygen: A
literature review and treatment algorithm
H.
Murphy-Lavoie , F. Butler , C. Hagan
UHM 2012, Vol. 39, No. 5:943-953
ABSTRACT
Central retinal artery occlusion (CRAO) is an
uncommon eye disorder, but one that typically produces severe and irreversible
vision loss in the affected eye. The retina has a dual blood supply, with the
retinal circulation supplying the inner layers and the choroidal circulation
supplying the outer layers. In CRAO, vision loss results from cell death in the
inner retinal layers despite relative sparing of the outer layers.
If supplemental oxygen is provided, however,
oxygen from the choroidal circulation may diffuse in adequate quantity to the
inner layers of the retina to maintain retinal function and restore vision. In
some patients this can be achieved with normobaric hyperoxia; in others,
hyperbaric oxygen (HBO2) may be required.
The challenge is to provide the supplemental
oxygen early enough after the onset of vision loss to prevent irreversible
damage to the retina. In experimental models of complete CRAO, the ischemic
time window before permanent retinal damage occurs is just over 90 minutes; in
the clinical setting where occlusion may be incomplete, return of vision may be
achieved even after delays of eight to 24 hours.
In patients with a clinical picture of CRAO who present within 24 hours of
vision loss, supplemental oxygen should be started immediately at the highest possible
fraction of inspired oxygen (FiO2). If vision is not quickly restored, emergent HBO2 should be undertaken if feasible. If the patient responds to HBO2, follow-up treatment with supplemental oxygen should be
customized to maintain retinal viability until the obstructed retinal artery
recanalizes, which typically occurs within the first 72 hours. This paper
reviews the pertinent literature on CRAO and HBO2 and provides a treatment algorithm.
Based on the American
Heart Association classification of evidence, treatment of CRAO with hyperbaric
oxygen therapy is Level IIb . There is fair
to good evidence to support its use with retrospective case series but no prospective
randomized controlled trials. It is acceptable, safe, considered efficacious
but lacks confirmation of efficacy by
Level 1 studies. There is no evidence of harm, and consistently positive
results, when HBO2 is started shortly
after onset on vision loss. In addition, there are no alternative therapies
with similar outcomes, that would present ethical considerations for a proposed
randomized trial. The relatively rare incidence of this condition does not lend
itself to randomized controlled trials, as evidenced by the paucity of trials
for other therapies in treating this condition. As of 2012, a Medline search revealed only four small randomized
controlled trials for all of the proposed therapies, none
of which revealed clinically positive results. The hopeless and recalcitrant nature of this
condition when left untreated mandates we utilize all potentially helpful treatments,
including hyperbaric oxygen therapy.
