Transient Visual Loss

168 Clinical Pathways in Neuro-Ophthalmology, second edition

Figure 8–1. Evaluation of monocular transient visual loss (TVL).

Does Monocular TVL Occur Only in Certain

Positions of Gaze (Gaze-Evoked TVL)?

Patients who experience TVL evoked by eccentric position of gaze (gaze-evoked TVL) usually have an intraorbital mass that intermittently compresses the circulation to the optic nerve or retina (Bremner, 1999; Danish-Meyer, 2001; Knapp, 1992; Kohmoto, 1993; Mezer, 1997; Smith, 1998). The visual loss immediately clears when the direction of gaze is changed. The most common lesions are orbital cavernous hemangiomas or optic nerve sheath meningiomas. Other orbital lesions producing this sign include osteomas, neurofibromas, gliomas, medial rectus granular myoblastoma, metastases, varices, orbital trauma, thyroid eye disease, and intraocular foreign body (buckshot pellet). The examination may be normal or show evidence of an optic neuropathy with an afferent pupil defect, color vision impairment, disc edema, and optociliary collateral vessels. Other signs of orbital tumor, such as proptosis, limitation of extraocular muscle

170 Clinical Pathways in Neuro-Ophthalmology, second edition

Figure 8–2. (continued )

movement, swelling of the eyelids, chemosis, and conjunctival congestion, may be evident. Evaluation requires magnetic resonance imaging (MRI) or computed tomography (CT) scans of the orbital structures. Intermittent visual loss and exophthalmos may occur with bending over or the Valsalva maneuver (Sobottka Ventura, 2001). Gazeevoked monocular TVL has also been noted in patients with pseudotumor cerebri

(O’Duffy, 1998). It has been hypothesized that in an eccentric position of gaze, ischemic compression of a tense dilated optic nerve sheath results in elevation of intrasheath pressure compromising blood flow to the retina or optic nerve (Miller, 1991; O’Duffy, 1998).

Does the Visual Loss Occur After Prolonged

Reading (Reading-Evoked TVL)?

Reading may also induce monocular TVL. Manor et al described a 49-year-old man with a 5-year history of dimming of central vision in the left eye provoked only during reading (Manor, 1996). An orbital apex tumor situated lateral to and above the optic nerve was found. This reading-evoked visual dimming may be a variant of gaze-evoked TVL. The optic nerve, displaced laterally and superiorly and stretched by the act of reading, may have been compressed between the tumor and the contracted inferior rectus muscle. Thus, orbital neuroimaging is appropriate in patients with readinginduced TVL.

Intermittent angle closure glaucoma may cause TVL, and reading-induced TVL has been reported in one case. O’Sullivan et al described a 66-year-old patient with episodes of monocular TVL lasting 3 minutes to several hours that were precipitated by reading, writing, or watching television (O’Sullivan, 1995). Ophthalmologic exam was normal but reading over 4 hours induced corneal edema, a poorly reactive semidilated pupil, and a shallow anterior chamber with intraocular pressure of 50 mm Hg. The intermittent angle closure glaucoma and the patient’s symptoms were treated successfully by iridotomies.

Do the Episodes of Monocular TVL Last

Seconds?

Episodes of TVL lasting less than 60 seconds may occur in patients with papilledema (Wall, 1991). These transient obscurations of vision may occur in one or both eyes (individually or simultaneously) and typically last only a few seconds, though in rare cases they may last for hours. The episodes may be precipitated by changes in position, and are thought to be related to the effects of increased intracranial pressure on the flow of blood to the eye, perhaps where the central retinal artery penetrates the optic nerve sheath to enter the substance of the nerve (Miller, 1991). Similar monocular TVL lasting seconds may occur in optic nerve sheath meningiomas unrelated to increased intracranial pressure. The pathogenesis of these episodes in meningioma is unknown and may be caused by the effect of the meningioma on the central retinal artery where it enters the optic nerve (Miller, 1991). Transient obscurations of vision may also occur in an eye with congenital abnormalities of the optic disc, such as peripapillary staphyloma (see below), or optic disc drusen. A case of ice-pick headaches associated with monocular visual loss with scintillating scotoma lasting seconds has been described in a patient with a history of migraine with visual aura (Ammache, 2000). The patient was treated with oxygen inhalation and indomethacin with complete resolution of the symptoms. Finally, carotid atherosclerotic disease may rarely cause very brief episodes

172 Clinical Pathways in Neuro-Ophthalmology, second edition

of transient visual loss, but more often attacks of TVL with carotid disease last 2 to 15 minutes (see below).

Patients with transient visual obscurations first require ophthalmologic examination. If papilledema is evident (Chapter 7), these patients must have an MRI scan of the brain. If this study is normal, a spinal tap is indicated to investigate the possibility of infection or pseudotumor cerebri (idiopathic intracranial hypertension). Patients with drusen or other optic disc anomalies causing monocular TVL may require no further evaluation. If there are signs of an optic neuropathy on the side of the TVL (e.g., relative afferent pupillary defect, ipsilateral swollen or atrophic optic nerve, etc.), then MRI with attention to the orbit is warranted to evaluate a compressive lesion. Patients without apparent disc abnormalities should be screened for carotid atherosclerotic disease or other sources of emboli (see below). In selected cases, MRI should be performed to investigate the possibility of a structural brain lesion such as optic nerve sheath meningioma.

Do the Episodes of Monocular TVL Last

Minutes?

Monocular TVL lasting 5 to 60 minutes (usually 2 to 30 minutes) is strongly suggestive of thromboembolic disease. Retinal emboli may arise from the aorta (Romano, 1998), the carotid artery, or the heart. Patients often describe the TVL as a veil or shade descending or ascending over a portion of their visual field. Other patients complain of patchy visual loss (‘‘Swiss cheese’’ pattern) or peripheral constriction with central visual sparing (Bruno, 1990). Some episodes of monocular TVL are accompanied by a sensation of color or other photopsias. These may superficially be similar to migraine, consisting of showers of stationary flecks of light that disperse quickly (Bruno, 1990; Goodwin, 1987; Pessin, 1977). Most episodes of embolic monocular TVL last 2 to 30 minutes. Marshall and Meadows found that in 51 of 67 patients (76%) episodes lasted 30 minutes or less, with 29 patients (43%) experiencing episodes lasting 5 minutes or less (Marshall, 1968). Pessin et al noted that attacks lasted less than 15 minutes in 30 of 33 patients, and in 14 patients (42%) the episodes lasted 5 minutes or less (Pessin, 1977). Among 35 patients evaluated by Goodwin et al, 22 patients (63%) had attacks lasting 5 minutes or less, 8 (23%) had episodes lasting 6 to 15 minutes, and 6 patients (17%) had episodes lasting more than 15 minutes (Goodwin, 1987). Episodes of monocular TVL due to thromboembolic disease rarely last several hours.

Patients with thromboembolic disease may demonstrate emboli within the retinal vessels. Emboli may be composed of clotted blood, fibrin, platelets, atheromatous tissue, white cells, calcium, infectious organisms (septic emboli), air, fat, tumor cells, amniotic fluid, or foreign materials (e.g., talc, artificial valve material, catheters, silicone, cornstarch, mercury, corticosteroids). The most common types of emboli seen in atherosclerotic disease of the aorta=carotid arteries or cardiac disease include the following:

1.Cholesterol emboli (Hollenhorst plaques) are bright, glistening, yellow or coppercolored fragments, most often seen in peripheral arterioles in the temporal fundus. These emboli most often arise from atheromatous plaques in the aorta or carotid bifurcation.

2.Platelet-fibrin emboli are dull, white, gray, often elongated, and subject to fragmentation and distal movement. These emboli most often lodge at bifurcations of retinal vessels and arise from the walls of atherosclerotic arteries or from the heart, especially from heart valves. They may also be seen in coagulopathies.

3.Calcific emboli tend to be large, ovoid or rectangular, and chalky-white. These emboli often occur over or adjacent to the optic disc. They usually arise from cardiac (aortic or mitral) valves and less often from the aorta or carotid artery. Unlike cholesterol emboli, which often disappear in a few days, calcific emboli may remain permanently visible.

Sharma et al found the sensitivity and specificity of visible retinal emboli for the detection of hemodynamically significant (defined as greater than or equal to 60%) carotid stenosis to be 39% and 68%, respectively, in patients with acute retinal artery occlusion (Sharma, 1998). The presence of a visible embolus generated a likelihood ratio of 1.24, whereas the absence of a visible embolus generated a likelihood of 0.88. The authors concluded that the presence of a visible embolus is a poor diagnostic test for the detection of hemodynamically significant carotid artery stenosis in the setting of acute retinal artery occlusion. Klein et al described the prevalence at baseline and the 5-year incidence of retinal emboli in the Beaver Dam Study. They reported the associated risk factors, the relationship of retinal emboli at baseline to stroke, and ischemic heart disease mortality in these patients. The study consisted of 4,926 patients, aged 43 to 86 years at baseline (Klein, 1999). The prevalence of retinal emboli at baseline was 1.3% and the 5-year incidence was 0.9%. The prevalence of retinal emboli was associated with high pulse pressure, hypertension, diabetes mellitus, past and current smoking, cardiovascular disease, and the presence of retinopathy. Patients with retinal emboli had a significantly higher risk of dying with stroke than those without retinal emboli.

TVL may also occur from ocular hypoperfusion rather than embolization. In some patients, monocular TVL may occur when the patient is exposed to bright light. These patients usually have severe, ipsilateral carotid occlusive disease. Bilateral, simultaneous TVL induced by exposure to bright light may rarely occur with bilateral severe carotid stenosis or occlusion (Kaiboriboon, 2001). The light-induced TVL probably reflects the inability of a borderline ocular circulation to sustain the increased retinal metabolic activity associated with light exposure. Alternating transient visual loss to bright light has also been described with giant cell arteritis (Galetta, 1997).

One prospective study assessed the clinical features of monocular TVL and the likelihood of atherosclerotic lesions of the internal carotid artery (ICA) (Donders, 2001). Of the 337 patients, 159 had a normal ICA on the relevant side, 33 had a stenosis of 0 to 69%, 100 had a stenosis of 70 to 99%, and 45 had an ICA occlusion. An altitudinal onset or disappearance of symptoms was associated with atherosclerotic lesions of the ipsilateral ICA. A severe (70 to 99%) stenosis was also associated with duration of TVL between 1 and 10 minutes, and with a speed of onset in seconds. An ICA occlusion was associated with attacks being provoked by light, an altitudinal character, and the occurrence of more than 10 attacks.

TVL may also occur with carotid artery dissection. In a review of the clinical features of 146 patients with extracranial carotid artery dissection, 41 patients (28%) had monocular TVL. The TVL was painful in 31 cases, associated with a Horner’s syndrome in 13 cases, and described as ‘‘scintillations’’ or ‘‘flashing lights’’ (often related to

174 Clinical Pathways in Neuro-Ophthalmology, second edition

postural changes suggesting choroidal hypoperfusion) in 23 cases (Biousse, 1998b). Two of 23 patients with spontaneous carotid artery dissection experienced transient monocular blindness; in one of these patients, episodes were provoked by sitting up from a supine position (Kerty, 1999).

Postprandial transient visual loss has also been described (Levin, 1997). In one patient, episodes of splotchy visual loss occurred unilaterally on the left 1 hour after eating her largest meal of the day. The episodes lasted approximately 3 hours and were occasionally accompanied by numbness and weakness of the contralateral arm. Severe left carotid stenosis was noted. In a second patient, blotchy bilateral transient visual loss episodes lasting 2 minutes to 1.5 hours were precipitated by eating or standing from a sitting or lying position. This second patient was found to have complete occlusion of the right carotid artery and moderate stenosis of the left carotid artery. The authors proposed that postprandial visual loss may be a symptom of critical carotid stenosis, with retinal and choroidal hypoperfusion probably caused by a combination of mesenteric steal, decreased cardiac output, and abnormal vasomotor control (Levin, 1997).

Venous stasis retinopathy (hypotensive retinopathy), associated with severe carotid or ophthalmic artery occlusive disease, may also be associated with TVL (Gass, 1997). This syndrome is characterized by visual loss and ischemic retinal infarction often accompanied by signs of ciliary artery obstruction, pallor of the disc, and hypotony. Venous stasis retinopathy may simulate Purtscher’s retinopathy (multifocal areas of ischemia) and be associated with a variety of fundus pictures (Gass, 1997):

1.Minimal or no ophthalmoscopic changes in some patients with monocular TVL.

2.Few widely scattered blot and dot hemorrhages and mild dilation of retinal veins (venous stasis retinopathy), usually in patients with minimal visual complaints.

3.Dilation of the retinal arterial tree, dilation of the retinal veins, and cotton-wool patches.

4.Retinal capillary changes, including microaneurysms, cystoid macular edema, and angiographic evidence of areas of capillary nonperfusion that may be confined to the areas along the horizontal raphe.

5.Larger areas of peripheral capillary nonperfusion, retinal neovascularization, and hemorrhage.

6.Any degree of branch retinal vein occlusion, branch retinal vein occlusion, branch retinal artery occlusion, and central retinal artery occlusion.

7.Ischemic optic neuropathy.

8.Fluorescein angiography showing diffuse retinal capillary telangiectasia, delayed retinal artery circulation time, late staining of the disc, and aggregations of microaneurysms around the preequatorial zone mimicking idiopathic juxtafoveal retinal telangiectasia.

9.Any of the above associated with panuveitis, neovascular glaucoma, and a rapidly progressing cataract (ocular ischemic syndrome).

Venous stasis retinopathy may be difficult to differentiate from central retinal vein occlusion (CRVO). Helpful differentiating features include the following:

1.The retinal veins are irregular in caliber with venous stasis retinopathy.

2.Hemorrhages, microaneurysms, and capillary dilations are often peripheral rather than in the posterior pole with venous stasis retinopathy (with CRVO these changes are often diffuse rather than peripheral).

3.Venous stasis retinopathy is not associated with disc edema or optociliary veins (compared with CRVO).

The ocular ischemic syndrome (Gass, 1997; Malhotra, 2000) is a progressive disorder due to hypoperfusion of eye that may be associated with TVL and ocular discomfort or frank pain localized to the orbit and upper face that is often decreased when the patient lies down. Rubeosis iridis in an older nondiabetic patient without evidence of venous obstructive disease or other predisposing cause is suggestive of the ocular ischemic syndrome. In persons over the age of 50 with new-onset iritis, the possibility of ocular ischemic syndrome should be considered. It is usually due to atherosclerotic carotid or ophthalmic artery disease. Other less common causes for venous stasis retinopathy and the ocular ischemic syndrome include giant cell arteritis, carotid artery dissection, cavernous sinus thrombosis, Takayasu’s disease, fibromuscular dysplasia, mucormycosis, herpes zoster ophthalmicus, myelofibrosis, vasospasm, and postaneurysm repair (Borruat, 1993; Casson, 2001; Gupta, 1990; Hamed, 1992; Hwang, 1999; Lewis, 1993; Meire, 1991; Winterkorn, 1995; Zimmerman, 1995). Four of seven patients with maxillofacial arteriovenous malformations (AVMs) that had been treated previously with proximal ligation of the supplying external carotid artery had signs of ocular ischemia (Andracchi, 2000). These four patients had significant ophthalmic artery supply by the malformations, suggesting that when the ophthalmic arterial blood supply is recruited, an ophthalmic artery ‘‘steal’’ phenomenon occurs, causing ocular ischemia. This ‘‘steal’’ may be precipitated or worsened by previous surgical proximal ligation of external carotid arterial branches that are potential collaterals with the ophthalmic artery but fail to occlude the arteriovenous shunt.

Giant cell arteritis (GCA) may produce attacks of TVL lasting minutes to hours indistinguishable from those produced by atheromatous disease (Hayreh, 1998a,b) (see Chapter 5). TVL probably results from intermittent inflammatory occlusion of the ophthalmic, posterior ciliary, or central retinal arteries. A postural form of TVL has been described in giant cell arteritis and a tenuous optic disc perfusion (Wykes, 1984). Alternating monocular TVL may occur with GCA (Finelli, 1997) and may be induced by bright light (Galetta, 1997).

TVL may also occur in association with antiphospholipid antibodies, hyperviscosity and hypercoagulable states, polycythemia vera, systemic lupus erythematosus (SLE), and hepatitis C–associated type II cryoglobulinemia-mediated systemic vasculitis with mononeuritis multiplex. AVMs may divert blood flow from or reduce blood flow in the ophthalmic artery (ophthalmic steal syndrome) (Case Records of the MGH, 1999; Donders, 1998; Levine, 1990). The TVL may alternate from eye to eye. Donders et al noted that TVL occurred in 6% of patients with SLE (Donders, 1998). In patients with SLE, there was no relationship between TVL and the presence of antiphospholipid antibodies or livedo reticularis. Five of 10 patients with SLE had TVL in either eye (alternating TVL).

Vasospasm, especially associated with migraine, may also produce TVL without any of the visual phenomena typically seen during a migraine attack (Bernard, 1999; Booy, 1990; Burger, 1991; O’Sullivan, 1992; Winterkorn, 1993). Vasospasm of the retinal vessels has been documented by ophthalmoscopy during some attacks of monocular TVL. TVL, likely due to vasospasm and migraine, may be induced by exercise or sexual intercourse (Jehn, 2002; Teman, 1995). Exercise-induced TVL may last minutes to hours (Jehn, 2002). TVL in young individuals is often benign and related to migraine. Tippin et al reviewed

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83 cases of TVL or ocular infarction before age 45 years. These authors found that cerebral transient ischemic attacks occurred in nine patients but no case of stroke was found (Tippin, 1989). Forty-one percent of the patients had headaches or orbital pain accompanying their TVL spells and an additional 25.3% had severe headaches independent of the visual loss. Of the original 83 patients, 42 were reexamined after a mean period of 5.8 years. None of the patients in this group had a stroke. The clinical status at follow-up did not correlate with duration of visual loss (TVL or ocular infarction), frequency (single or recurrent episodes), gender, presence of headache or heart disease, cigarette smoking, use of oral contraceptives, or abnormal findings on echocardiogram or blood studies. The authors concluded that TVL and ocular infarction occurring in the younger patient are probably associated with a more benign clinical course than that seen in older persons, and that migraine is a likely cause for visual loss in a majority in this group. O’Sullivan et al described nine young adults (median age 19.5 years) who suffered from TVL (O’Sullivan, 1992). The attacks of TVL were short in duration and associated with premonitory symptoms in five patients and a migrainous headache in two. In five patients the visual loss progressed in a lacunar pattern (vision was lost in a series of blobs), unlike the ‘‘curtain’’ pattern characteristic of TVL in older patients. Investigation revealed no evidence of an embolic or atheromatous etiology. In two patients a minor abnormality was found on echocardiography. The authors conclude that TVL in young adults has a different clinical pattern and may have a different etiology, possibly migraine, compared with that seen in older patients. The pattern of visual loss in some of the cases suggests that the choroidal circulation rather than the retinal circulation is primarily affected.

TVL lasting 15 to 20 minutes (occasionally up to 7 hours) may occur during episodes of spontaneous anterior chamber hemorrhage (hyphema) (Kosmorsky, 1985; Miller, 1991). In these patients TVL may be associated with erythropsia (seeing red) and color desaturation. Such hemorrhages are most likely to occur after cataract extraction and are particularly apt to occur after placement of an iris fixation lens implant. Other potential causes of spontaneous anterior chamber hemorrhages include vascular anomalies of the iris (e.g., in myotonic dystrophy or Sturge-Weber syndrome), microhemangiomas, diffuse hemangiomatosis of childhood, neoplasms (e.g., melanoma or retinoblastoma), diseases of blood or vessels (e.g., leukemia, hemophilia, scurvy, lymphoma), rubeosis iridis, severe iritis, fibrovascular membranes, juvenile xanthogranuloma, occult trauma or delayed bleeding after trauma, hydro-ophthalmos, malignant exophthalmos, histiocytosis X, and postsclerotomy with cautery (Kosmorsky, 1985). Episodes of TVL lasting up to 24 hours have been described with recurrent hyphema after deep sclerotomy with collagen implant (DSCI) (Ambresin, 2001). The uveitis-glaucoma-hyphema (UGH) syndrome is an unusual cause of monocular TVL following cataract extraction and intraocular lens implantation (Cates, 1998). Patients may present with the full triad or with its individual elements, with symptoms often developing at an interval, often years, after cataract surgery. Table 8–1 compares the symptoms of TVL in retinal emboli compared with the UGH syndrome (Cates, 1998).

Intermittent angle closure glaucoma may also cause brief episodes of monocular TVL that are usually, though not always, associated with ipsilateral eye pain and occasionally simultaneous dilation of the pupil (Miller, 1991). Exercise-induced visual disturbances may also occur during attacks of pigmentary glaucoma (Jehn, 2002). Episodes of monocular TVL lasting 2 to 3 minutes induced by changes in posture have been described following scleral buckle procedure, likely due to intermittent obstruction of

Table 8–1. Comparison Between the Classic Symptoms of Visual Loss in Patients with Transient Visual Loss (TVL) Due to Retinal Emboli and the Uveitis-Glaucoma-Hyphema (UGH) Syndrome

the central retinal artery blood flow by the encircling element (Fineman, 1999). Finally, TVL may also be associated with the congenital anomalies, peripapillary staphyloma, and morning glory syndrome (Ebner, 1995; Gass, 1997; Zarnegar, 1995). Episodes of TVL with these anomalies may last 15 to 20 seconds (obscurations of vision) or up to 20 minutes, the latter mimicking TVL with thromboembolic disease. The episodes of TVL in peripapillary staphyloma may be associated with intermittent dilation of the retinal veins and may be orthostatic.

Patients with monocular TVL lasting minutes associated with visible retinal emboli need to be evaluated for carotid and aortic vascular disease and cardiac valvular disease. Stroke risk factors (e.g., smoking, hypertension, diabetes mellitus, hyperlipidemia, etc.) should be evaluated and controlled. Studies to evaluate the carotid arteries include carotid Doppler and ultrasound. Some patients may require MR angiography and conventional angiography. Cardiac investigations include transthoracic and transesophageal echocardiography and cardiac MRI. In a study of 18 patients with branch or central retinal artery occlusion, transesophageal echocardiogram revealed a possible cardiac or thoracic source of embolus in 13 patients (72%), whereas a potential carotid source of embolus was present in three of 16 patients (19%) (Kramer, 2001).

Hurwitz et al performed a prospective clinical and arteriographic study comparing patients with monocular TVL and patients with other transient hemispheral cerebral ischemic attacks (Hurwitz, 1985). In their 93 patients with monocular TVL, a potentially operable atherosclerotic carotid lesion (defined as 5 50% stenosis or ulceration on the side of TVL) was found in 66% of the patients, and the 7-year cumulative rate of cerebral infarction in these patients was 14%. In 212 patients with other hemispheric transient ischemic attacks, an operable carotid lesion was found in 51% of patients, with the 7-year cumulative rate of infarction 27%. Therefore, in approximately two thirds of patients with monocular TVL, a potentially operable carotid lesion may be found.

In patients with monocular TVL (or other carotid distribution transient ischemic attacks or nondisabling stroke) and ipsilateral carotid stenosis of 70 to 99%, carotid endarterectomy may be indicated. Surgery may be recommended in this setting if the patient is a good surgical candidate and the perioperative morbidity and mortality of the surgeon is in the 2% or less range (North American Symptomatic Carotid Endarterectomy Trial Collaborators, 1991). Carotid endarterectomy in this group reduces the 2-year ipsilateral stroke rate from 26 to 9%, and decreases the major or fatal ipsilateral stroke rate from 13.1 to 2.5%. The benefit of surgery in the 70% or greater

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stenosis patients is greatest among men, in patients with a recent stroke as a qualifying event, and in patients with hemispheric (versus visual) symptoms (Barnett, 1998). The benefit of surgery is twice as great for patients with 90 to 99% carotid stenosis versus 70 to 79% stenosis. The frequency of major functional impairment was much lower in the surgical group than in the medical group (Haynes, 1994). In patients with monocular TVL, other carotid distribution transient ischemic attack or nondisabling stroke, and 50 to 69% ipsilateral carotid stenosis, the 5-year rate of any ipsilateral stroke was 15.7% in the surgical group and 22.2% in the medical group (Barnett, 1998). Among patients with < 50% stenosis, the stroke rate was not significantly lower in the surgery group (14.9%) than in the medical group (18.7%). Therefore, carotid endarterectomy in patients with symptomatic carotid stenosis of 50 to 69% yields only moderate reduction in stroke risk, with the absolute risk reduction being about 10% at 5 years. Among patients with internal carotid artery stenosis, the prognosis is better for those presenting with transient monocular blindness than for those presenting with hemispheric transient ischemic attacks (Benavente, 2001). Decisions about treatment must take into account the recognized risk patient factors, and the surgical perioperative complication rates must be 6% or less. In the patient with less than 50% carotid stenosis, a cardiac or aortic embolic source should be sought and, if none is found, the treatment is aspirin plus control of stroke risk factors. In patients with emboli from a cardiac valvular source, especially those with cardiac dysrhythmias such as atrial fibrillation, anticoagulation is warranted if the patient is an appropriate medical candidate. Patients older than 55 years with a history of monocular TVL lasting minutes without visible retinal emboli should have an evaluation for giant cell arteritis (e.g., erythrocyte sedimentation rate, temporal artery biopsy) (class II, level C).

Patients with evidence of monocular TVL resulting from ocular hypoperfusion (e.g., venous stasis retinopathy and the ocular ischemic syndrome) might have decreased retinal artery pressure on ophthalmodynamometry. The patient should be investigated for carotid stenosis and, if this is insignificant, ophthalmic artery stenosis or occlusion is inferred. When carotid stenosis is severe, endarterectomy may be used to reestablish flow (Kawaguchi, 2001; Rennie, 2002); when the internal carotid artery is totally occluded, a superficial temporal artery to middle cerebral artery bypass procedure may be considered if the external carotid is patent (Kawaguchi, 1999). With early treatment, resolution of the hypoperfusion syndrome may occur; unfortunately, no therapy is clearly effective. In one study, carotid endarterectomy was effective for improving or preventing the progress of chronic ocular ischemia caused by internal carotid stenosis; visual acuity improved in 5 of 11 patients and had not worsened in the other 6 (Kawaguchi, 2001). Reestablishment of flow in a previously stenotic internal carotid artery may actually produce further visual difficulties by increasing perfusion to the ciliary arteries and causing dramatic increase in intraocular pressure. Carotid endarterectomy or superficial temporal artery to middle cerebral artery bypass procedure have been combined with laser panretinal photocoagulation, peripheral retinal cryotherapy, or both. These latter procedures are thought to decrease the oxygen requirement of the eye and thus reduce the drive for neovascularization. Rarely, the ocular ischemic syndrome may be improved by the calcium channel blocker, verapamil (Winterkorn, 1995).

If no thromboembolic source for the episodes of TVL is documented, then further studies should be considered. These include MRI of the brain with MR angiography to investigate for possible brain ischemia or less likely a vascular malformation, and

laboratory studies, including sedimentation rate, complete blood count, antiphospholipid antibodies, antinuclear antibodies, collagen vascular disease profile, and studies to investigate the presence of dysproteinemia (class III–IV, level U).

Young patients (< 45 years old) with monocular TVL are unlikely to have significant carotid disease. A cardiac embolic source as well as a vasculitis or coagulopathy must be sought. As noted above, monocular TVL in younger patients has a more benign clinical course than that found in an older population, and migraine is a likely cause for many episodes. Calcium channel blockers (e.g., verapamil or nifedipine), if not otherwise contraindicated, may be considered in some of these patients to reduce the frequency of episodes of TVL (Teman, 1995; Winterkorn, 1993).

Finally, all patients with monocular TVL lasting minutes should have a complete ophthalmoscopic examination to investigate such conditions as intermittent angle closure glaucoma, morning glory syndrome, and peripapillary staphyloma. Spontaneous anterior chamber hemorrhage (hyphema) should also be considered, especially in patients with associated erythropsia and in those who have undergone cataract extraction.

Episodes of monocular TVL lasting hours are rare. However, such spells may occur with thromboembolic disease, as a postprandial phenomenon associated with critical carotid stenosis, and with migraine. Monocular TVL lasting hours may be a symptom of impending central retinal vein occlusion (Biousse, 1997).

An approach to the evaluation of patients with monocular TVL is presented in Figure 8–1.

Are the Episodes of TVL Binocular?

Transient visual obscurations lasting seconds may occur in one or both eyes in patients with increased intracranial pressure and papilledema. Also, patients with bilateral severe carotid occlusive disease may rarely have bilateral TVL on exposure to bright light. Otherwise, episodes of bilateral simultaneous TVL are usually due to migraine, bilateral occipital lobe ischemia (e.g., vertebrobasilar insufficiency), or other occipital lesions.

The presence of a small area of visual loss or a mild disturbance of vision that progressively increases over 15 minutes or longer (march and buildup) is highly characteristic of migraine (Russell, 1996). This visual abnormality is usually bilateral and homonymous. The patient need not have headaches for this diagnosis to be made. Most patients describe abnormal positive visual symptoms associated with the episodes. Most commonly, fortification spectra are described around an area of scotoma. These scintillations or distortions within the area of visual disturbance may resemble ‘‘heat waves’’ or ‘‘water running down a glass.’’ The typical migraine visual aura starts as a flickering, uncolored, zigzag line in the center of the visual field that gradually progresses and expands toward the periphery of one hemifield and often leaves a temporary scotoma (Fisher, 1999). A migrainous visual accompaniment often occurs in individuals over age 50 and often occurs in the absence of headache in this age group (Wijman, 1998). These episodes probably are not associated with an increased stroke risk. The spells are usually stereotyped, begin gradually, and progress, last several minutes to 1 hour, and usually include positive visual phenomena (bright images, colors, movement of images) and affect both eyes. In a study by Wijman et al, the

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migrainous visual accompaniments were never accompanied by headache in 58% of patients, and 42% of individuals had no history of recurrent headache (Wijman, 1998). The risk of stroke in these patients was 11.5%, significantly less than the 33.3% noted in patients with transient ischemic attacks but not significantly different from the rate of 13.6% in those with neither migrainous accompaniments nor transient ischemic attacks. Associated symptoms may include nausea, aphasia, eye pain, diplopia, dizziness, tinnitus, numbness, and paresthesias.

Rarely, the positive visual phenomena of migraine may persist for months to years, unassociated with electroencephalographic or MRI findings (Liu, 1995). Patients with persistent migrainous visual phenomena (migraine aura status) may demonstrate occipital hypoperfusion on brain single photon emission tomography (SPECT) (Chen, 2001; Luda, 1991). This persistent migrainous phenomena may be responsive to lamotrigine (Chen, 2001). In another form of migraine aura status, patients may experience a large number of consecutive (mostly) visual auras, very often without headache. Between the auras, the patient is without symptoms. Episodes can last for weeks, and within this period several migraine auras can occur on one day. Haan et al described three such patients with migraine aura status treated successfully with acetazolamide (Haan, 2000).

Abnormal visual disturbances similar to those with migraine, often associated with headache, may rarely occur with cerebral structural lesions, such as AVMs of the occipital lobe or brain tumors, but these usually do not have the characteristic buildup and resolution of visual symptoms. Instead, these lesions usually produce symptoms that steadily increase in frequency and duration until they are present daily.

Occipital lobe tumors may rarely produce scintillating scotomas that mimic migraine (Biousse, 1998a; Miller, 1991; Pepin, 1990; Riaz, 1991). In most of these cases, the tumors were diagnosed only after the patients eventually developed papilledema or when a homonymous visual field defect was documented. Riaz et al described three patients with classical migraine for many years’ duration that preceded the diagnosis of meningioma (Riaz, 1991). In two patients, the tumors were occipital and in one frontotemporal. Visual symptoms in two of these patients were exceptional by their constant localization to the same hemianopic field, whereas in the third patient they involved either hemianopic field. The visual phenomena sometimes occurred independent of headache.

Arteriovenous malformations of the occipital lobes may also produce visual symptoms and headache that may simulate migraine (Haas, 1991; Kupersmith, 1996, 1999; Kurita, 2000; Spierings, 2001). Visual symptoms with occipital AVMs are usually brief, episodic, unformed, and not associated with the angular, scintillating figures that occur with migraine. They also tend to occur consistently in the same visual field. However, the clinical symptoms classically noted with migraine may occasionally occur with occipital AVMs. Kupersmith et al described the clinical presentations of 70 patients with occipital AVMs (Kupersmith, 1996). At the time of presentation, headache was present in 39 (56%); the headache was throbbing in 19 cases (27%) with preceding homonymous positive visual phenomena with migraine-like features in the field contralateral to the AVM in 15 cases. A visual disturbance in the opposite field, not necessarily associated with headache, occurred in 39 patients (56%). Patients often described episodes of scintillating scotomas, jagged flickering fortification images, transient and permanent homonymous hemianopia, blurred vision in a hemifield, hemifield spots, tunnel vision, and diplopia. Three patients had transient field loss as a prodrome to grand mal

seizures and two others had episodes of flickering vision associated with seizure activity on electroencephalography. Only 5 of the 23 patients with visual symptoms who had a homonymous field defect did not have recurrent headaches. Fifteen additional patients without visual symptoms, 8 of whom had no recurrent headaches, had homonymous visual field defects. The authors concluded that if ‘‘migraine’’ headache or visual symptoms are restricted to one side of the head (even if the visual field exam is normal), then a neuroimaging study should be performed to investigate the possibility of an occipital AVM. Migraine in this setting is a diagnosis of exclusion. Whereas some features of headache and visual symptoms are similar for occipital AVMs and migraine, the two disorders are usually distinguishable. Kurita and Shin described a man with periodic right-sided throbbing headaches heralded by a visual prodrome of scintillating bright lights in the left visual field lasting several minutes (Kurita, 2000). The headaches decreased 18 months after radiosurgery for a right occipital AVM. Positive visual phenomena resembling migraine have also been described with cerebral venous sinus thrombosis (Newman, 1989). Finally, scintillating scotomas occasionally occur in patients with SLE, but it is not clear if they are a manifestation of a cerebrovascular disorder related to lupus or simply the coexistence of two separate disease processes (Miller, 1991).

Panayiotopoulos et al described nine patients with idiopathic occipital epilepsy and visual seizures (Panayiotopoulos, 1999). The ictal elementary visual hallucinations were stereotyped for each patient, usually lasting seconds. They consisted of mainly multiple, bright colored, small circular spots, circles, or balls. Mostly, they appeared in a temporal hemifield, often moving contralaterally or in the center, where they may be flashing. They may be multiple and increase in size in the course of a seizure and may progress to extraoccipital manifestations and convulsions. Blindness occurred usually from the beginning and postictal headache, often indistinguishable from migraine, was common. Three of nine patients had ictal blindness as the only seizure manifestation. Most patients responded to carbamazepine. Elementary visual hallucinations in occipital seizures are entirely different from the visual aura of migraine. They are mainly colored, have a circular pattern, have the same onset regarding localization, are often brief (lasting seconds, occasionally minutes), develop rapidly, and then individual components may multiply or move together to the contralateral side. They often occur daily and may be associated with other seizure manifestations. Conversely, the visual aura of migraine start with predominantly flickering achromatic or black and white (rarely colored) linear and zigzag patterns in the center of vision that gradually expand over minutes toward the periphery of one hemifield and often leave a scotoma. Migraine rarely occurs daily.

Dreier et al described two patients with migraine who experienced migrainous auralike symptoms several minutes after the onset of acute headache induced by subarachnoid hemorrhage (Dreier, 2001). The cases suggest that subarachnoid hemorrhage is a trigger for migrainous aura.

Symptoms similar to the scintillating scotomas of migraine may also occur with acute vitreous or retinal detachment (Miller, 1991). In these patients, the visual symptoms are clearly monocular, last longer than typical migrainous visual aura, and occur without any associated headache. Scintillating scotomas, as well as monocular TVLs, have also been described associated with internal carotid artery dissection (Biousse, 1998b; Ramadan, 1991). The first of the three patients described by Ramadan et al developed sudden severe right occipital headache followed minutes later by nausea and bright

182 Clinical Pathways in Neuro-Ophthalmology, second edition

dots in both visual fields that spread centrifugally during a 10-minute period and persisted for several hours (Ramadan, 1991). The second perceived scintillating and nonmarching ‘‘snowflakes’’ in the entire visual field of the right eye that lasted 10 minutes, during which time the right eye lost vision. This was followed by right frontotemporal sharp pain that lasted for another hour. The third patient noted the abrupt onset of seeing stationary, sharp-edged gray shapes (triangles, squares, and zigzag lines), outlined in bright red and blue and superimposed on a glaring background. These positive visual phenomena were perceived in the left eye and lasted for 3 days. She later developed another episode of visual phenomena in the left eye associated with left supraorbital and temporal throbbing headache. The first patient’s episode was binocular but atypical for classic migraine in that the positive visual phenomena lasted for hours; in the other two patients the symptoms were monocular, and in one of these the positive symptoms lasted for days, again atypical features for classic migraine. As noted above, in a study of 146 patients with extracranial carotid artery dissection, 41 patients (28%) had transient monocular visual loss that was described as ‘‘scintillations’’ or ‘‘flashing lights’’ (often related to postural changes suggesting choroidal hypoperfusion) in 23 cases (Biousse, 1998b).

Patients with restrictive thyroid ophthalmopathy may occasionally complain of flashing lights in the superior visual field on upgaze, possibly phosphenes as a result of either compression of the globe by a tight inferior rectus muscle or traction on the insertion of the inferior rectus muscle (Danks, 1998). Twelve of 30 patients with thyroid ophthalmopathy had flashing lights on upward gaze and all had tight inferior rectus muscles (Danks, 1998).

Binocular episodes of TVL may be due to bilateral occipital ischemia secondary to disease of the vertebrobasilar circulation (rarely bilateral retinal ischemia from systemic hypotension or bilateral carotid disease). Episodes of visual loss or blurring in patients with vertebrobasilar transient ischemic attacks (TIAs) usually occur in association with other symptoms of transient brainstem, cerebellar, or posterior cerebral ischemia, including vertigo, dysarthria, dysphagia, diplopia, weakness, sensory disturbances (especially perioral numbness), coordination difficulties, and gait instability. Visual loss or blurring of vision in these patients is bilateral and symmetric, may be hemianopic or diffuse, and usually lasts several minutes or occasionally less than a minute (but not seconds, as noted with obscurations of vision noted with papilledema and increased intracranial pressure). The scintillating and expanding scotomas of migraine rarely occur with vertebrobasilar TIAs, and migrainous visual phenomena usually last 20 to 30 minutes, somewhat longer than visual loss noted with vertebrobasilar TIAs. Also, Hilton-Jones et al described a patient with a large frontal lobe tumor who experienced frequent, stereotyped episodes of bilateral, simultaneous visual loss lasting 5 to 30 minutes (Hilton-Jones, 1982). This patient reportedly did not have papilledema.

Other unusual causes of transient bilateral visual loss should be mentioned. For example, transient bilateral blindness lasting minutes to hours may rarely occur with giant cell arteritis, due to either vertebrobasilar insufficiency or bilateral impending anterior ischemic optic neuropathy (Diego, 1998). Bilateral blurred vision lasting minutes to several hours during sexual arousal may be associated with narrow-angle glaucoma (Friedberg, 1999). As noted above, transient bilateral blindness may be the sole manifestation of occipital epilepsy (Panayiotopoulos, 1999). In fact, prolonged (48 hour) visual loss may occur with occipital seizures (status epilepticus amauroticus)

(Sawchuk, 1997). Transient bilateral cortical blindness lasting 24 hours has been described with preeclampsia (Kesler, 1998), and transient cortical blindness lasting hours, days, or even several weeks may occur after cerebral angiography (Gibson, 1982). Temporary bilateral blindness (pupils normal or nonreactive) may occur with irritability, confusion, bradycardia, nausea, hypertension, dyspnea, and seizures during or after transurethral prostatic resection (TURP) (Barletta, 1994). This TURP syndrome is thought due to excessive absorption of nonelectrolyte irrigating fluid through the prostatic venous sinuses into the general circulation. Glycine toxicity on the optic nerves or cortex, due to excessive glycine absorption, is the likely mechanism of visual loss. The symptoms and signs of the TURP syndrome resolve within 24 hours with intravenous pyridoxine and arginine hydrochloride.

Bilateral TVL lasting several weeks may occur with the reversible posterior leukoencephalopathy due to immunosuppressive therapy (cyclosporine or tacrolimus) after transplantation. Patients on interferon-a for myeloma or interleukin-2 therapy for malignancy or HIV disease may develop TVL. TVL may occur in eclampsia, acute hypertensive encephalopathy associated with renal disease, or acute intermittent porphyria (Hinchey, 1996; Karp, 1996; Kuperschmidt, 1995).

What Is the Evaluation for Binocular TVL?

The evaluation of patients with bilateral TVL depends on a thorough history, especially directed at the characteristics and temporal course of the episodes of TVL and any associated symptoms, and a complete neuro-ophthalmologic examination, including visual field testing. If the episodes last seconds and papilledema is present, then MRI is indicated. If MRI is negative, then a spinal tap is warranted. If episodes of bilateral visual loss occur only on exposure to bright light, then evaluation of the carotid arteries is indicated. Patients with typical expanding migraine scintillations and positive phenomena lasting 20 to 30 minutes that have been noted to occur on different sides at different times and headaches that have been documented to occur on different sides at different times usually do not require further workup. Abnormalities on visual field examination suggesting a retrochiasmal lesion or atypical migraine-like phenomena should prompt neuroimaging (class III–IV, level C). Patients with visual symptoms that are brief, episodic, unformed, and not associated with the angular, scintillating figures might also require MRI or MR angiography (class III–IV, level U). When either ‘‘migraine’’ headache or visual symptoms are restricted to one side of the head (even if the visual field exam is normal), a neuroimaging study for occipital AVM is reasonable (class III–IV, level U). Patients with migraine and symptoms or signs of collagen vascular disease require a collagen vascular disease profile. Electroencephalography or a trial of anticonvulsant medications is warranted if occipital epilepsy is likely (class III, level U).

The evaluation and treatment of patients with vertebrobasilar TIAs is controversial. MRI and MR angiography are usually suggested, especially to evaluate the vertebrobasilar circulation, and intraarterial angiography may be considered. A cardiac embolic source should always be considered and, if warranted, transthoracic or transesophageal echocardiography may be performed (class III–IV, level C). Treatment includes control of stroke risk factors and antiplatelet drugs or anticoagulation.

184 Clinical Pathways in Neuro-Ophthalmology, second edition

An approach to the evaluation of patients with bilateral TVL is presented in Figure 8–2.

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