Introduction
Learning Objectives:
·
To review the epidemiology, pathophysiology and
presentation of retinal artery occlusion
·
To review evidence behind treatment options for
retinal artery occlusion
·
To review the concept of disease prevention in
epidemiology
Time Credit:
2 Hours
Case
A 76 year old female presents with a 24 hour history of
decreased vision in her left eye.
She says the vision loss occurred suddenly, and has not had any other
symptoms such as flashes, floaters, or pain in the eye. Her ocular history is significant for
cataract surgery in both eyes over ten years ago, while her medical history is
significant for longstanding hypertension and dyslipidemia. On exam, visual acuities are 20/25 in
the right eye and 20/40 in the left eye.
Intraocular pressure and anterior segment exam are normal in both
eyes. The fundus appearance of the
left eye is shown below.
What is the most likely
diagnosis?
• Branch retinal artery occlusion
CORRECT
• Central retinal artery occlusion
INCORRECT - in the fundus photograph one can clearly see that the blockage is distal to the bifurcation of the central retinal artery. A central retinal artery occlusion would typically present with a worse visual acuity than the case in question.
• Branch retinal vein occlusion
INCORRECT - The fundus appearance is consistent with an arterial rather than venous occlusive pathophysiology, the latter of which classically appears as “blood and thunder.”
• Central retinal vein occlusion
INCORRECT - The fundus appearance is consistent with an arterial rather than venous occlusive pathophysiology, the latter of which classically appears as “blood and thunder.”
Introduction
Retinal artery occlusion is an important cause of vision
loss in the elderly, and is caused by any event causing significant blockage of
a retinal artery. Such a blockage
is termed either a central retinal artery occlusion (CRAO) or branch retinal
artery occlusion (BRAOs) depending on whether the occlusion occurs before or
after the bifurcation of the retinal artery, respectively. Central retinal artery occlusions occur
at an incidence of approximately 0.85 cases per 100,000 per year,1 with BRAOs being less
common. Of all retinal artery
occlusions, CRAOs account for 58% of cases, BRAOs for 38% and cilioretinal
artery occlusions for the remaining 5%.2 There is a slight male predominance.
Anatomy
A clear understanding of the blood supply to the retina is imperative
in understanding the pathophysiology of a retinal artery occlusion. The outer retinal pigment epithelium
and photoreceptors are supplied mainly by the choroid, which gets its vascular
supply from ciliary arteries which themselves originate from the ophthalmic
artery (a branch of the internal carotid artery). On the other hand, the inner neural retina is supplied
mainly by the central retinal artery, the first intraorbital branch of the
ophthalmic artery which enters the optic nerve 8-15 mm behind the globe. In 14% of the population, a
cilioretinal artery branching from the short posterior ciliary is present,
providing additional blood supply to the macula from the choroidal circulation.
Etiology
Retinal artery occlusion is the result of any event causing
obstruction of the retinal vasculature and corresponding infarction of the
inner retina. While most cases
occurring in elderly individuals are thromboembolic in origin, there are
numerous potential causes of retinal arterial occlusion that must be considered
especially in the young (<40 years old) or atypical patient.
Briefly, the causes of retinal artery occlusions include:
· Emboli: emboli are a common
cause of retinal artery occlusion, and are usually of calcific, cholesterol (“Hollenhorst”),
or platelet-fibrin composition.3 There may be a history of amaurosis fugax
or transient ischemic attack, especially in the presence of carotid artery
disease. The most common sources of
embolus is a carotid artery plaque, but cardiac lesions (e.g. aortic or mitral
vavular lesions) or other cardiac pathology such as patient foramen ovale,
tumor in the left atrium, or myxoma may produce emboli.3, 4 Rarely, intravenous drug users may have
BRAO or CRAO secondary to talc.
· Intraluminal thrombi: occlusion may
be due to an unstable thrombus or hemorrhage into thrombus
· Vasculitic/inflammatory: Any
vasculitis of small or medium size arteries (e.g. temporal arteritis, takayasu
aortitis, systemic lupus erythematosus, polyarteritis nodosa, Wegener’s
granulomatosis, Churg-Strauss disease) has the potential to cause retinal
artery obstruction.5 The most common vasculitic etiology is
temporal (giant cell) arteritis, which causes 1-2% of cases of CRAO (often
termed “arteritic” as opposed to “non arteritic” CRAO).6
· Infectious: toxoplasmosis,
mucormycosis, syphilis, dengue fever have been reported to be associated with
retinal artery occlusion.7
· Thrombophilic disorders:
antiphospholipid antibody syndrome, protein S/C deficiencies, and hematologic
malignancies (i.e. lymphoma, leukemia) can all cause thrombophilia leading to
retinal artery occlusion.
Antiphospholipid antibiody syndrome is associated especially with
multiple BRAOs and should be considered in the young patient.
· Hypoperfusion: significant internal
carotid stenosis may cause hypoperfusion in the setting of a drop in blood
pressure.3
· Raised intraocular pressure: raised
intraocular pressure from even causes such as pressure on the eye during
surgery have been reported to cause retinal artery occlusion
· Vasospasm: vasospasm secondary to
retinal migraine (a subtype of ophthalmic migraine) or cocaine use may cause
retinal artery occlusion8-10
Risk Factors
Risk factors for thromboembolic CRAO are virtually identical
to those of systemic atherosclerosis and include diabetes mellitus, smoking,
renal disease, arterial hypertension, ischemic heart disease, and TIA/strokes.3, 11 Studies have shown that the majority of
patients with CRAO have a systemic vascular condition,12, 13 with 75% having evidence of atherosclerosis11 and 45% having carotid
atherosclerosis in the form of an ipsilateral plaque or stenosis.14 Another study found that nearly 50% of
patients with CRAO have a structural
cardiac abnormality.15
Presentation
The typical presentation of CRAO is a patient with sudden,
painless, and profound vision loss.
A recent history of amaurosis fugax is not uncommon. Although most commonly unilateral, bilateral
CRAO occurs in 1-2% of cases.13 The condition most commonly occurs in
the seventh decade but can occur in younger patients especially with valvular heart lesions or thrombophilia.12
Approximately 90% of patients with CRAO have vision between
counting fingers and light perception at presentation.13 A relative afferent pupillary defect is
often present within seconds of onset.6 Initially, the fundus exam will appear
unremarkable, however the retina will take on the classic white-yellow
appearance with a cherry red spot over the macula (it usually takes at least 1
hour for this to occur). The white
appearance is due to ischemic necrosis, inner layer edema, and pyknosis of the
ganglion cell nuclei. The cherry
red spot is due to a combination of a thin nerve fibre layer and nourishment
from the underlying choroid. In
25% of cases of CRAO, a patent cilioretinal artery supplying the papillomacular
bundle is present; such patients typically have a slightly better visual acuity
at presentation.16 Retinal vessels may appear
attenuated or segmented (“box carring” or “cattle-tracking”). In its late stages, the whitish-yellow
appearance of the retina is replaced by a homogenous scar.
Retinal emboli are seen in 20-40% of cases of CRAO,17 and the appearance of
such emboli can suggest its origin.
While glistening yellow emboli are often from atherosclerotic plaques
within the carotid arteries, calcific emboli typically originate from cardiac
valves.6, 18 Large nonglistening platelet-fibrin
emboli are commonly seen at the optic disc.6, 19
With BRAOs, more than 90% occur in the temporal retinal arteries, although it is debatable
as to whether there is a true predominance for the temporal arteries, or such
arteries are more likely to be symptomatic.2 Presenting visual acuity depends on the
location of the occlusion, especially in relation to the macula.