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CURRENT OPHTHALMOLOGY
Year : 2001  |  Volume : 49  |  Issue : 1  |  Page : 5-14

Carotid artery disease and ocular vascular disorders


1 MS,DNB. Kannuri Santhamma Retina Vitreous Centre, L.V. Prasad Eye Institute, Hyderabad, India
2 MS. Kannuri Santhamma Retina Vitreous Centre, L.V. Prasad Eye Institute, Hyderabad, India
3 MD DM. Kannuri Santhamma Retina Vitreous Centre, Department of Neurology, Nizam's Institute of Medical Sciences, Hyderabad, India

Correspondence Address:
Nazimul Hussain
MS,DNB. Kannuri Santhamma Retina Vitreous Centre, L.V. Prasad Eye Institute, Hyderabad, India

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Source of Support: None, Conflict of Interest: None


PMID: 15887709

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Keywords: Carotid artery disease, ocular ischaemic syndrome, anterior ischaemic optic neuropathy, transient monocular visual loss, carotid endarterectectomy


How to cite this article:
Hussain N, Jalali S, Kaul S. Carotid artery disease and ocular vascular disorders. Indian J Ophthalmol 2001;49:5-14

How to cite this URL:
Hussain N, Jalali S, Kaul S. Carotid artery disease and ocular vascular disorders. Indian J Ophthalmol [serial online] 2001 [cited 2020 Apr 5];49:5-14. Available from: http://www.ijo.in/text.asp?2001/49/1/5/22665

* REFERENCE NOS. 1, 6, 12

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* REFERENCE NOS. 1, 6, 12

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Carotid artery obstruction is the most common abnormality associated with ocular vascular insufficiency or ischaemic syndrome. Obstruction may be due to atheromatous plaque, external compression, arteritis, or dissection of the artery. However, an atheromatous lesion of the carotid artery is the most frequent underlying lesion responsible for chronic inadequate vascular supply to the globe resulting in ocular ischaemic syndrome (OIS). It is estimated that more than 50% of patients with OIS have significant, demonstrable carotid artery occlusion or stenosis at the time of presentation.[1-4]


  Background Top


In 1961, Hollenhorst proposed the significance of retinal emboli, which are seen as bright orange cholesterol plaques [Figure - 1] at the bifurcation of retinal arterioles in 11% of 235 patients with carotid artery occlusive disease.[2] Two years later Kearns and Hollenhorst reported ocular signs and symptoms occuring secondary to severe carotid artery, disease, [5,6] and termed this condition "Venous stasis retinopathy". There was confusion over this term, since mild central retinal vein obstruction was also designated as "venous stasis retinopathy", which was a distinctly different entity. Hence, the term "ocular ischaemic syndrome" was later coined to describe clinical features in eyes seen in association with chronic carotid artery obstructive disease. [5,6]


  Predisposing factors Top


Various carotid artery diseases can give rise to ocular ischaemia. Atherosclerosis accounts for most of the cases responsible for OIS. [1, 5, 6] Stenosis or obstructive lesions are due to atheromatous plaque thickening.[6] Characteristic signs and symptoms of OIS are associated with severe hypoperfusion of the eye, which usually reflects severe carotid occlusive disease. [1,4] Embolic ischaemic optic neuropathies and compression of the intracranial optic nerve by supraclinoid carotid arteries remain debated as a cause of OIS.[7] It is generally believed that 90% or greater ipsilateral carotid artery stenosis is necessary to induce ocular ischaemia secondary to carotid artery obstruction.[6] It has been shown that a 90% obstruction of the carotid artery reduces the perfusion pressure within the corresponding central retinal artery by about 50%. [8,9] This obstruction can affect either the common carotid system or the internal carotid artery. Ophthalmic artery obstruction has also been reported as a cause of OIS. These are due to emboli dislodged from the atheromatous plaque of carotid artery. [1,6]

Inflammatory lesions causing aorto-arteritis involving the aortic arch and the common carotid are also responsible for decreased flow in the carotid system. Giant cell arteritis in OIS has been reported by Hamed et al.[10] In this study they excluded haemodynamically significant stenosis of the internal carotid artery as the cause of OIS, in patients with giant cell arteritis. Duker and Belmont[11] reported ocular ischaemia secondary to carotid artery dissection. Harino and associates reported OIS secondary to Eissenmenger syndrome.[12] It has been suggested that systemic hypoxia without hypoperfusion can lead to neovascular response.[12] Barral and Summers[13] reported an extremely rare case of OIS in a 19-month-old child with Moyamoya disease and neurofibromatosis. In such a setting, ocular ischaemia is not expected and may go unrecognised. Carotid occlusion can be associated with CNS vasculopathy in Moyamoya disease and has been frequently reported in the Japanese population.[13] The carotid artery can be affected by numerous other disorders such as fibromuscular dysplasia, spontaneous or traumatic dissection and radiation, Takayasu's arteritis, external compression or rarely, emboli from heart and coagulation disorders.[14]


  Clinical presentations Top


Carotid artery disorders, mainly atheromatous lesions, can give rise to ocular ischaemia, seen in elderly patients aged 50-80 years. No racial predilection is seen or identified. Men appear to be affected more than women by a ratio of 2:1. [3, 6, 15, 16]


  Symptoms Top


Patients with carotid artery disease may present with transient or monocular ipsilateral ocular symptoms and signs that can herald a devastating cerebral stroke.[14] Asymptomatic retinal emboli, transient monocular visual loss (TMVL), and central retinal artery occlusion are the most common clinical presentations. In the later situations, the patient would present with transient or profound sudden onset of visual loss.[14] Other patients may present with slow onset of unexplained visual loss or visual loss with minimum ocular signs. Mizener et al[3] reported 39 eyes of 32 patients with OIS where 41% of the eyes presented with sudden loss of vision, 15% with amaurosis fugax, and 13% with ocular or orbital pain; 21% were asymptomatic.

TMVL (also called Amaurosis fugax) is the most common and perhaps the most frequently reported ocular symptom of carotid artery occlusive disease. Patients usually complain of partial or complete, acute onset monocular visual loss.[14] It usually manifests as a sudden, painless, temporary monocular visual loss lasting as short as 2 minutes to as long as 30 minutes and is usually followed by complete recovery. The ocular examination between episodes shows either normal retinal anatomy or abnormalities confined to the retinal vasculature only. The association between amaurosis fugax and ipsilateral carotid artery disease was first noted by Fisher.[17] He reported the association of TMVL with subsequent development of contralateral hemiplegia and emphasized the high incidence of occlusion of internal carotid artery (ICA) in these individuals. Subsequently he reported platelet fibrin emboli in the retinal circulation of a man with TMVL.[18]

Lesions of common or internal carotid artery usually cause TMVL by embolising material to retinal circulation. With emboli, a black or dark shade sweeps across the visual field of the affected eye, disappearing after few minutes. Occasionally emboli may be observed ophthalmoscopically as they traverse the retinal arterioles.[19] Severe stenosis of the carotid circulation result in retinal and or choroidal hypoperfusion and hence less commonly cause transient visual loss. Intermittent thrombosis mechanisms owing to reduced blood flow have been reported in patients with extreme narrowing of the carotid artery.[20] Emboli are the aetiologic agents usually invoked for cases in which carotid stenosis is less marked.[19]

Some patients may remain asymptomatic despite significant carotid artery obstructive lesions associated with slow onset of reduced blood flow to the eye producing anterior or posterior segment ischaemia or both. This can occur when critical hypoperfusion is not achieved to manifest permanent ocular symptoms or signs. Until such stage is reached, certain situations which reverse the flow of shunt with increased demand of perfusion in other regions may give rise to transient ischaemia with visual symptoms. [5, 14, 16]

A positive visual phenomenon is also induced by situations that either decrease perfusion pressure such as postural change or increase retinal oxygen demand such as exposure to bright light. Postprandial transient visual loss has been reported by Levin and Mootha[16] in two patients with severe carotid disease. The probable mechanism was combination of mesenteric steal, decreased cardiac output, and abnormal vasomotor control in the presence of severe carotid disease resulting in reduced perfusion pressure of retinal-choroidal circulation. Visual phenomenon due to exposure to bright light reflects the inability of borderline ocular circulation to sustain the increased retinal metabolic activity. Thus chronic hypoperfusion of the eye probably induces delay in the regeneration of visual pigments in the photoreceptors resulting in blurred vision or transient blindness that persists until pigments are regenerated.[21]

In some patients with severe carotid artery stenosis and nonfunctional collateral circulation, the compromised circulation is adequate to supply both the eye and the brain. In this situation minimal changes in the systemic arterial pressure, rise in venous pressure, rise in intraocular pressure and stealing or diversion of blood flow may shift the flow from one direction to the other. Situations which reduce systemic blood pressure may also alter cerebral autoregulatory mechanisms thereby leading to changes in ophthalmic artery blood flow. [14,22]

The major immediate complication of TMVL is irreversible visual loss, mostly due to occlusion of central retinal artery [Figure - 2] or its branches. In carotid artery occlusive disease, TMVL can herald a cerebral infarction. When carotid occlusive disease is related to atherosclerosis, TMVL is a marker of systemic atheromatous disease and therefore is associated with high risk of vascular death.[23]

In the event of slow onset of chronic ocular hypoperfusion secondary to a slowly progressive severe carotid occlusive disease, the ocular changes manifest as hypotensive retinopathy or sometimes as venous stasis retinopathy. Visual loss in such instances occurs insidiously in two-thirds of patients, but in approximately 12% of patients it may be abrupt, probably due to central retinal artery obstruction. The slow visual loss could be painful or painless. Pain encountered in 40% of patients with OIS[1] is usually described as a dull ache localised either to the eye or the periorbital region, that may typically get better in the supine position.[22] The term "ocular angina" has been used to describe this type of pain. The probable causes of ocular angina are ischaemia of the globe, increased IOP due to neovascular glaucoma [Figure - 3], dural ischaemia or a combination of the three. In some cases of carotid artery disease, patients may experience referred pain from the carotids to the orbital region, but without obvious ocular involvement. This is rare in patients with atheromatous lesions, but is more often seen in carotid dissection.[14] Rarely, patients can present with severe pain due to neovascular glaucoma.


  Signs Top


At presentation, the visual acuity is variable in patients with OIS. Approximately 43% of eyes initially have 6/6 to 6/15 vision whereas 37% have counting fingers or less. Negative light perception is unusual but can develop later in the course of the disease. Whether treated or not, approximately one-fourth of patients maintain 6/6 to 6/15 vision at the end of one year while nearly 60% have counting fingers or worse vision.[1] Mizener et al[3] described that 64% of eyes had visual acuity worse than or equal to 6/120 (20/400) and 15% had visual acuity of 6/12 (20/40) or better, at the initial visit.

Neovascularisation of the iris (NVI) often develops in eyes with acute central retinal vein occlusion or other small vessel retinal disease. However, NVI [Figure - 3] can also occur in eyes with chronic hypoperfusion due to carotid artery obstruction. It may be present in approximately two-thirds of eyes with OIS at the time of the initial visit. Mizener et al[3] reported NVI in 34 of 39 eyes with OIS at the time of presentation.

It is known that severe carotid artery disease precipitates ocular ischaemia due to chronic ophthalmic artery insufficiency. This insufficiency eventually leads to NVI and gives rise to neovascular glaucoma. However, many patients of OIS and NVI do not show any sign of retinal capillary dropout or retinal neovascularisation. It has been suggested that uveal ischaemia alone could be responsible for NVI in such eyes. This may follow release of vasoproliferative agents from chronically ischaemic iris and probably posteriorly from ischaemic peripheral retina and choroid. Brown et al[5] reported 12 eyes with NVI in patients with carotid obstructive disease or central retinal artery occlusion. Whether choroidal ischaemia in addition to retinal ischaemia increases the risks of producing ocular neovascularisation is not known. Choroidal hypoperfusion may produce outer retinal ischaemia in addition to choroidal ischaemia and produce stimulus for iris neovascularisation. There may be other factors contributing to the NVI. In ICA obstruction, the blood flow may occur to the ipsilateral brain via the retrograde flow from the external carotid artery. It could produce an ophthalmic artery steal syndrome, which in effect shunts blood away from the globe and contributes to ischaemia.[24] Decreased blood flow to the eye results both from the blocked ICA and secondarily induced ophthalmic steal effect.

Anterior chamber flare is present in most eyes with rubeosis iridis. Sometimes, an anterior chamber cellular response can also be seen. It is generally mild but keratic precipitates can develop. This occurs due to poor endothelial cell barrier function of the new vessels in the iris.

The venous stasis manifests in dilated, but not tortuous retinal veins, peripheral microaneurysms and blossom-shaped haemorrhages in the midperipheral retina. These are the most common fundus changes of chronic ischaemia in carotid obstruction. The retinal arteries are generally narrowed and occasionally the entire retina appears featureless with white thread-like arteries. This presentation is often mistaken as a normal retina if the examination is not meticulous and complete. Venous beading [Figure - 4] is also seen but not as much as in diabetic patients.

Dot and blot retinal haemorrhages are seen approximately in 80% of affected eyes. They are larger and darker than those seen in diabetic retinopathy. They are most commonly seen in the midperipheral retina but can extend into the far periphery or into the posterior pole. However, they are less numerous than those seen in other vascular diseases of retina and are often not confluent.

Retinal microaneurysms can be seen in the posterior pole but are more likely in the midperipheral retina. Posterior segment neovascularisation could occur on the optic disc (NVD) (30-35%) or elsewhere in the retina (NVE) (80%). Vitreous or subhyaloid haemorrhage occurs from rupture of new vessels. Other lesions seen are cotton wool spots, retinal arterial pulsations and cholesterol emboli. The arterial pulsations may extend a disc diameter or more from the nerve head into the surrounding retina. [1, 14, 25]

Ischaemic optic neuropathy in patients with carotid artery disease [Figure - 5] results from emboli in the posterior ciliary vessels, pial vessels or both.[26] It also results from reduced perfusion pressure secondary to severe carotid occlusive disease and poor collateral blood supply. [4, 8, 27, 28] The [Table - 1] shows the symptoms and signs seen with OIS. [1, 6, 12]

Before the advent of modern imaging systems such as computer tomography (CT) and magnetic resonance imaging (MRI), it was popular to consider compression of the intracranial optic nerve by supraclinoid carotid arteries as the cause of progressive unilateral or bilateral unexplained optic neuropathy. However, MRI studies have shown that in asymptomatic patients with an unexplained optic neuropathy, though the supraclinoid artery frequently comes in contact with the intracranial optic nerve, anatomic compression is infrequent. [7,8] The risk of optic nerve compression is directly proportional to the diameter of the carotid artery.[7]

Acute carotid artery occlusion may give rise to third-order Horner's syndrome secondary to damage to the sympathetic pathway distal to the superior cervical ganglion. It is presumed to be due to both ischaemia (via vasa nervosum) and compression (enlarged occluded carotid) of the pericarotid sympathetic fibres. It has been reported in patients with atheromatous occlusion of ipsilateral carotid artery, but is more common in carotid artery dissection. [8, 24, 29] Rarely, acute ocular motor palsy can reveal occlusion of ipsilateral ICA. It has been reported in patients with atheromatous carotid disease and carotid artery dissection.[30-32]

In low-tension glaucoma (LTG) because of histologic similarities between the cavernous degeneration of the optic nerve and cerebral lacunar state in patients with cerebral small vessel disease, it has been suggested that LTG may be a small vessel disease of the optic nerve.[33-36] However, Muller et al[37] in their comparative study with retinal ischaemic syndrome (RIS) and anterior ischaemic optic neuropathy (AION) found that patients of RIS and AION had proven ischaemic eye disease mostly of atherosclerotic macro-or microangiopatnic origin. They have demonstrated that LTG exhibits no striking association with significant atherosclerotic carotid artery stenosis. They have also shown that hemispheric cerebral ischaemia ipsilateral to the affected eye was significantly rarer in LTG patients than in RIS patients. Vascular risk factors except high blood pressure were less frequent in LTG patients than in RIS and AION patients. Jampol and associates also found no evidence of LTG in their prospective study of 18 patients who had survived multiple episodes of hypertension and shock.[38]


  Systemic associations of OIS Top


The clinical manifestations of OIS are often seen in patients with associated systemic diseases such as diabetes and hypertension. Hence misdiagnosis is likely with diabetic retinopathy, arterial occlusion, and hypertensive retinopathy. The important clues to an underlying carotid artery aetiology are: marked asymmetry of retinopathy, gross disproportion in the extent of anterior and posterior segment pathology, and disproportionate visual loss along with other signs and symptoms mentioned in the table.

Sivalingam et al[4] have reported association of systemic arterial hypertension and diabetes mellitus in 73% and 56% respectively in patients with OIS. By the time of presentation for ocular problems, patients with OIS may have already experienced a stroke (TIA), myocardial infarction or peripheral vascular disease. [1,11] Mizener et al[3] have reported increased incidence of systemic arterial hypertension, coronary artery disease, stroke or TIA, and diabetes mellitus in patients with OIS compared to general population. Cigarette smoking has also been attributed to be an associated finding. [1,14]


  Diagnostic Workup Top


When carotid artery disease is suspected in a patient with ocular signs and symptoms, a prompt noninvasive vascular workup is mandatory to confirm the carotid disease, establish its cause (atheroma, dissection, vasculitis, compression), assess the severity of lesion (percentage of stenosis or occlusion) and its ocular and cerebral tolerance (hypoperfusion of the ipsilateral eye and cerebral hemisphere). These include cerebral angiography, arteriography, digital subtraction angiography, ultrasonography, doppler scan, magnetic resonance angiography and spiral CT angiography.


  Cerebral angiography Top


Cerebral angiography remains the gold standard to assess carotid atherosclerotic disease. [8,32] In a large series of 1010 patients with amaurosis fugax or amaurosis fugax and TIA, 23% had normal angiogram and 77% had varieties of abnormalities.[40] The observed abnormalities in angiogram included irregularity of the vessel walls (23%), stenosis (37%), occlusion (13%) and other abnormalities such as kinks, loops, and fibromuscular dysplasia (3%).


  Arteriography Top


Selective contrast arteriography is the most reliable method of demonstrating the carotid artery lesion. This method is limited by the requirement for the large volume of concentrated contrast material, relative insensitivity of radiographic film to small attenuation differences between tissues and contrast material, and the technical difficulty of the procedure. It also carries a 3.7% intraoperative and perioperative complication rate. [6, 14, 40, 41]


  Digital subtraction angiography Top


Intravenous digital subtraction angiography is safer and highly specific. In one study digital subtraction angiography demonstrated a lesion at the carotid bifurcation in 96% of the patients. While conventional angiography offers advantages in spatial resolution, digital subtraction angiography serves both as a screening and as a definitive preoperative angiography. It is most useful in the evaluation of the extracranial carotid arteries and of renovascular hypertension.[34] However, this procedure is ordered only when a patient is considered for carotid endarterectomy due to its specificity and demonstrable capability. [8, 10, 32, 42]


  Ultrasonography Top


Carotid ultrasonography is the mainstay of noninvasive evaluation of extracranial carotid artery disease. Carotid duplex scanning ([Figures:6] and [Figure - 7]) is more definitive where simultaneous real time B-mode ultrasound images [Figure - 7] are compared with single gated pulse doppler ultrasound [Figure - 6]. It can measure accurately the degree of extracranial stenosis and also provide information regarding local plaque morphology. Carotid duplex scanning cannot differentiate between 99% stenosis of carotid artery and complete occlusion. However, this distinction is important since the patient remains a surgical candidate even when the artery is marginally patent. [1, 8, 13, 32, 42]


  Doppler Scan Top


Conventional doppler scanning is not capable of describing the circulation of smaller calibre vessels within the retrobulbar space, including the ophthalmic, central retinal and short posterior ciliary arteries. The colour doppler imaging (CDI) on the other hand, facilitates study of the orbital vasculature by colour coding the doppler frequency shift of the blood flow, superimposing this colour on B-scan anatomic detail and thereby allowing localisation, orientation of vessel angles and flow velocity.[43] Using this imaging technique in patients with ipsilateral ICA disease, lesions' ranging from 70% stenosis to total occlusion have been reported.[42] Ho et al[42] demonstrated markedly reduced central retinal artery peak systolic blood flow velocity in all eyes with OIS. The CRA peak systolic blood velocity ranged from 1.3 to 6.0 cm/sec (mean 3.5 cm/ sec) while in the control group it was 10.3 ± 2.1 cm/sec. They also documented reversal of the ophthalmic artery blood flow in 12 of 16 eyes with OIS. The mean systolic blood flow velocity of the ophthalmic artery was 21.9 cm/sec whereas in controls it was 30.6 ± 8.9 cm/sec. The short posterior ciliary artery (SPCA) peak systolic blood flow velocity ranged from not detectable to 8.6 cm/sec. This was significantly less than the control group mean of 9.1 ± 2.6 cm/sec. Thus hypoperfusion of the globe secondary to carotid artery obstructive disease was convincingly demonstrated by CDI.[35] CDI is useful not only for evaluation of OIS but also in understanding the natural history and pathophysiology, and thereby forming the basis for rational treatment of this condition. [8, 10, 32, 42, 44]


  Magnetic resonance angiography (MRA) Top


Magnetic resonance angiography (MRA) is considered a sensitive technique in screening for carotid atherosclerosis and evaluating intracranial haemodynamics. It is probably as sensitive as duplex scanning in demonstrating extracranial carotid artery stenosis, but is not good at demonstrating plaque morphology. It is sometimes difficult to interpret and may overestimate the degree of stenosis. [8, 32, 42]


  Spiral CT angiography Top


Spiral CT angiography is another noninvasive technique that provides accurate depiction of blood column even in regions of extensive carotid artery stenosis, and may prove useful in patients with suspected carotid artery disease. [2, 42]


  Management Top


Treatment of OIS remains difficult and controversial. The therapeutic management is directed towards management of rubeosis iridis, neovascular glaucoma and restoring blood flow to the eye with surgery involving the carotid vascular system.


  Management of ocular neovascularisation Top


Most patients of OIS have underlying carotid artery obstructive disease and associated diabetes mellitus or systemic hypertension. Hence, fundus flourescein angiography is often ordered to determine the cause of NVI and /or neovascular glaucoma (NVG). As a disproportionate correlation exists between visual loss and anterior or posterior segment findings, panretinal photocoagulation (PRP) alone may not induce regression of neovascularisation or the neovascular glaucoma. [1, 4, 15] This is because the underlying cause of ocular ischaemia is still unattended, and uveal tissue ischaemia continues to release angiogenic agents. Hence, results of clinical trials of PRP for proliferative diabetic retinopathy cannot automatically be applied to OIS unless diabetic retinopathy is solely responsible for it.[5]

Results of anterior retinal cryoablation (ARC) as a treatment of OIS are not very well described in the literature. However, PRP with or without ARC still remains the initial modality of treatment of ocular neovascularisation in OIS.


  Management of neovascular glaucoma Top


In OIS, patients with NVG need to be treated to lower the IOP as much as possible so as to improve ocular perfusion, to prevent further loss from various types of vascular occlusion or glaucoma and control pain secondary to NVG. Medical control of IOP is preferred. However, we must remember that the underlying cause for ocular ischaemia persists. While aqueous suppressants and cycloplegics have been used, cyclocryotherapy, ARC, trans-scleral cyclophotocoagulation (TSCPC) and rarely retrobulbar alcohol injection to relieve pain are advocated in recalcitrant cases. In theory the possibility of IOP lowering exists with trabeculectomy, especially when combined with mitomycin C. [3,5]


  Management of Carotid Artery Disease Top


Once an underlying carotid artery dysfunction is identified, the patient should be evaluated by a neurologist and management decided as a team (ophthalmologists and neurologists). Treatment may be either medical or surgical.


  Surgical therapy Top


Surgical excision of the atheroma at the cervical carotid artery bifurcation, the "carotid endarterectomy" is an accepted surgical procedure of amaurosis fugax and other carotid artery distribution-related transient ischaemic attacks. It has become apparent that atherosclerotic lesions and ulcerated plaques are present in the carotid artery system in a majority of adults with TMVL and other TIAs. Most anterior circulation TIAs and strokes including those involving the eye are ascribed to carotid occlusion or embolism. Theoretically, excision of such lesion should be preventive. [1, 23, 45]

The NASCET (North American Symptomatic Carotid Endarterectomy Trial, 1991) study[45] has demonstrated that symptomatic patients with 70% or greater stenosis of internal carotid artery benefit from endarterectomy. Independently, the ECST (European Carotid Surgery Trial, 1991)[46] has also shown that surgery significantly reduces both morbidity and mortality rate in patients with high grade stenosis and recent ipsilateral neurologic event. However, in the NASCET study, patients with hemispheric and ocular events were grouped together for analysis. Hence, it was not clear if patients with ocular TIA alone were at high enough risk of stroke to qualify for endarterectomy. Further analysis of the NASCET data has shown that the estimated incidence of two-year ipsilateral stroke for hemispheric TIA was 43.5% and 16.6% for ocular TIA.[47]

Further, patients with ocular TIA alone did not suffer a single major stroke, defined as functional deficit persisting beyond 90 days. While the incidence of stroke per year in patients with ocular TIA was 8.5% in the NASCET study,[47] the other natural history study of Trob[48] estimates the incidence not more than 4% per year. Given the relatively benign progression of the disease, many physicians recommend that those patients with isolated ocular TIA be best managed with medical therapy alone, irrespective of the degree of stenosis, while others recommend endarterectomy, sometimes even in asymptomatic patients.[49-51] We recommend that patients with ocular TIA be subjected to endarterectomy only if the attacks are recurrent and / or are accompanied by hemispheric symptoms; and if the surgeon's surgical success rate is high.

Reports of the results of endarterectomy in eyes with OIS are few. Theoretically, increasing ocular circulation should cause regression of the neovascular response and improve IOP in hypotonic eyes or decrease IOP in eyes with NVG. But IOP may rise following endarterectomy if NVG is caused by angle closure by fibrovascular tissue. In such eyes, aqueous production is low, secondary to impaired ciliary body perfusion due to carotid stenosis. With sudden reversal of stenosis following endarterectomy, ciliary body perfusion improves and aqueous production increases but the anterior chamber still remains closed resulting in severe rise of IOP. [1, 4, 5, 16, 27, 31] Macular oedema also has been reported after carotid endarterectomy in OIS.[52]

While the ocular signs may reverse with improved perfusion following carotid endarterectomy the visual prognosis at the end of one year may still remain poor due to previous chronic damage.[4] There is at least one report[53] of NVI and NVG following endarterectomy. This rare complication could be due to reperfusion syndrome, sudden increase of blood flow in a previously ischaemic eye and circulation of angiogenic elements. This particular case reported by Nguyen et al[53] responded to PRP.

Patients with total carotid artery obstruction do not benefit from surgery. In such instances, the thrombus often propagates to the next major vessel. Earlier, extracranial to intracranial surgery was advocated but this has shown no benefit in preventing ischaemic strokes.[54] However, in cases of carotid bifurcation stances, external carotid artery endarterectomy with ligation of internal carotid artery is the procedure of choice. [49, 50]


  Medical therapy Top


Aspirin is the standard initial treatment. It inhibits platelet aggregation by blocking the cyclo-oxygenase pathway of platelet activation. Meta analysis of numerous studies has documented 20-25% risk reduction in stroke reccurence with aspirin.[55] The dose ranges from 75 to 1300 mg and no trial has shown difference in effectiveness according to dose. In view of gastrotoxicity at higher dosage, low to medium doses (75 to 325 mg) are preferable. The side effects include dyspepsia, tinnitus and gastrointestinal bleeding.

Ticlopidine inhibits platelet aggregation induced by adenosine diphosphate by blocking the glycoprotein IIb/III a and has been shown to be slightly more effective than aspirin.[56] However, it can cause rash, diarrohea and neutropenia. Regular monitoring of blood counts is usually warranted every 2 weeks for the first 3 months and less frequently thereafter. The recommended dose is 250 mg twice a day.

Dipyridamole is a platelet adhesion inhibitor, but the mechanism of action has not been fully elucidated. There is evidence to suggest that a combination of low dose aspirin (25 mg) and extended release dipyridamole (200 mg) is the most effective antiplatelet strategy at present, reducing the stroke risk by 37% compared to placebo.[57]

Clopidrogel is a new antiplatelet drug not available as yet in India. It also prevents platelet aggregation by inhibiting the glycoprotien II b / IIIa receptor. The safety and side effects profile for clopidrogel and aspirin are similar. Unlike Ticlopidine it does not cause neutropenia, but is far more expensive. The recommended dose is 75 mg per day.[58]

In conclusion, it is clear that the ophthalmologist plays an important role in early diagnosis of patients with ocular ischaemic syndrome and other ocular manifestations of carotid artery diseases. The disorders are often unrecognized and misdiagnosed as diabetic retinopathy, optic atrophy, brain tumour, central retinal artery or vein occlusion. Appropriate diagnosis coupled with systemic and ocular management can help decrease the fatality due to cerebral and systemic complications. Patients with visual loss disproportionate to the ocular findings especially with regards to neovascularisation of the iris, disc pallor and other ocular findings as shown in the table without classic diabetic and hypertensive retinopathy should be evaluated for carotid artery disease and OIS. Patients with TMVL or retinal artery occlusion also need carotid artery evaluation. Recommended workup would involve a thorough internist's examination (including myocardial disease or stroke), blood profile (sugar, electrolytes and proteins) and urine analysis (albuminuria). These patients should undergo carotid artery evaluation; the investigation usually recommended would be carotid duplex scan or colour doppler scan. If significant haemodynamic obstruction is noted, then either MRA or Spiral CT angiography can be advised in consultation with a neurophysician. Ocular treatment should be carried out simultaneously with the neurological treatment. Early diagnosis of such cases can reduce the morbidity and mortality rate by decreasing the incidence of stroke and myocardial infarction.



 
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    Figures

  [Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7]
 
 
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