Cerebral collateral circulation helps maintaining cerebral perfusion in acute ischemic stroke, the role of Primary collaterals (circle of Willis) is more evident; however, the role of secondary collaterals especially ophthalmic artery in predicting stroke outcome is controversial. Our study aimed to evaluate the role of ophthalmic artery flow in predicting stroke outcome.
Thirty patients with acute stroke and significant extracranial carotid stenosis were included in the study, we found that ROAF was present among 10 patient (33.3%), this was in agreement with the range appeared in previous studies, Grilo and colleagues studies ROAF in cases with carotid stenosis (967 cases), they found that the frequency of ROAF increase with increasing severity of stenosis being 43% in cases with > 80% stenosis, there was a significant association between ROAF and increasing severity of stenosis with excellent specificity and negative predictive value . Reynolds and colleagues found ROAF to be present in 56 out of 101 artery stenosis more than 80% . Tsai and colleagues Found it 25% in stenosis, 62.5% in occlusion .
In our study we divided the patients into two groups according to ophthalmic artery flow direction, we did not find significant difference in risk factors between patients with ROAF and FOAF.
As regard MRS which is a reflection of functional outcome, it was shown that patients with ROAF had better MRS after 3 months in comparison to FOAF, but not statistically significant. However, in comparing the difference between MRS after 3 months from discharge, it was statistically significant among ROAF group. This could suggest that ROAF might have a role in improving functional outcome, yet the results still non-significant comparing both groups which could be due to sample size.
The impact of ophthalmic artery in hemodynamics is still controversial, while some studies suggested that its presence indicates poor outcome due to impaired cerebral hemodynamics, others found it to save as compensatory mechanism in cases where the primary collaterals are insufficient. In Tsai and colleagues 2013, they found that the presence of ROAF was significantly related to poor functional outcome, and that the difference in hemodynamics in orbital arteries between stenotic side and the non-stenotic side indicates that ROAF act as a shunt to a low resistance intracerebral circulation due to impaired hemodynamics, or insufficient circle of willis ; however, it was different in methodology and follow up, also intracranial stenosis was present among 49.1% of all cases and 80% in ROAF patients, which was also found to be more significantly related to poor outcome.
Sung and colleagues investigated 128 subjects (101 with acute stroke, and 27 without stroke) with unilateral high-grade stenosis or occlusion, they found that acute stroke group had a significant higher percentage of ROAF, carotid occlusion, intracranial stenosis; however, multivariate analysis demonstrated that intracranial stenosis is the only significant risk factor. In addition, they found ROAF was present more among group without stroke and had combined extracranial and intracranial stenosis than group with stroke and combined stenosis, although it was not statistically significant, they suggested that the presence of ROAF might modify stroke risk in patients with combined extra and intracranial stenosis .
They then compare between four subgroups according to ophthalmic artery flow and intracranial stenosis; they found a trend towards better outcome from ROAF and mild or no intracranial stenosis. In addition, in patients with same degree of intracranial stenosis, stroke outcome improved by 10–20% in ROAF groups, suggesting that ROAF serve partial hemodynamics compensation, but still not complete protection against stroke risk due to small caliber and low blood flow in comparison with the arteries of circle of willis .
A more recent study tried to investigate effect of ROAF on midterm functional outcome following carotid artery stent, they found that stenting could be effective treatment option regardless the ophthalmic artery flow direction, and that patients without ROAF were more likely to have improved functional outcomes (16); however, the study design was different from ours and the outcomes were assessed after carotid artery stent which also affects the functional outcome.
Our study had some limitations, the small sample size, the assessment for extra cranial stenosis was done using duplex, CT angiography was not available for all patient and also the lack of conventional angiography; furthermore, the effect of intracranial stenosis and other collaterals were not investigated.