Optic Neuritis

Typical optic neuritis is an inflammatory optic neuropathy caused by demyelinating disease (Balcer, 2006) (Fig. 15.5). Visual loss in the affected eye typically occurs rapidly over several hours to a few days. Decreased color vision and contrast sensitivity are highly characteristic (Baier et al., 2005; Trobe et al., 1996). In addition, pain with eye movements precedes the vision loss in approximately 90% of cases (Optic Neuritis Study Group, 1991). The pain typically lasts 3 to 5 days; if it persists for longer than 7 days, optic neuritis should be considered less likely, and further workup should be pursued. Visual field defects commonly are present; they can be either diffuse or discrete scotomas and are nonspecific. Fundus examination reveals mild disc swelling in approximately one-third of affected eyes, which is considerably less prominent than the disc swelling associated with papilledema (Balcer, 2006; Beck, 1998) (Fig. 15.6). In the majority of patients, the fundus appearance is normal.

Fig. 15.5 Axial T1-weighted post-gadolinium MRI with fat saturation in a patient with right optic neuritis. Note swelling and enhancement of the right optic nerve (black arrow) consistent with inflammation.

(Reprinted with permission from Prasad et al., 2010.)

Fig. 15.6 Fundus photograph of the right eye in a patient with acute right optic neuritis. Note mild nerve fiber layer swelling, greatest at the temporal portion of the disc (black arrow), without hemorrhages or cotton-wool spots.

(Reprinted with permission from Prasad et al., 2010.)

The prognosis for recovery of vision generally is good but is in relation to the severity of the initial deficit. Recovery typically begins within 1 month. The likelihood of progression of optic neuritis to multiple sclerosis (MS) is best predicted by brain magnetic resonance imaging (MRI) at the time of diagnosis. In the Optic Neuritis Treatment Trial, the risk of developing MS within 15 years was 72% among patients with one or more characteristic brain lesions, whereas it was 25% if the MRI was normal (Optic Neuritis Study Group, 2008). With features that are atypical for optic neuritis, however (e.g., painless visual loss, severe disc edema, disc or peripapillary hemorrhages, macular exudate), the risk of developing MS is significantly lower (Beck et al., 2003).

Following an episode of optic neuritis, the optic nerve often demonstrates pallor, suggesting that axonal loss has accompanied the episode of demyelination (Fig. 15.7). Optical coherence tomography (OCT) is a noninvasive imaging method that quantifies the atrophy of the nerve fiber layer (Balcer, 2006). It provides a reliable structural marker that complements clinical assessments of visual function.

Fig. 15.7 Top, Fundus photographs of the left eye in a patient with prior left optic neuritis, demonstrating mild temporal pallor (black arrow). Below, Optical coherence tomography (OCT) measurement of retinal nerve fiber layer thickness confirms and quantifies temporal nerve fiber layer thinning (corresponding to the papillomacular bundle). Thickness measurement is shown in black line, with normal range depicted in green zone; measurements within the yellow zone are borderline, and within the red zone are abnormally low.

(Reprinted with permission from Prasad et al., 2010.)

Neuromyelitis optica (NMO), or Devic disease, is characterized by necrotizing demyelinating lesions of bilateral optic nerves and the spinal cord (Wingerchuk, 2006). It is believed to be a humorally mediated disease distinct from MS. The spinal lesion characteristic of NMO often extends contiguously over three or more vertebral segments. A serum antibody, neuromyelitis optica immunoglobulin G (NMO-IgG), which targets the autoantigen aquaporin 4 (AQP4), may be a useful marker in diagnosing the condition, although the exact specificity remains unknown (Jarius et al., 2008). Treatment with rituximab, a chemotherapeutic monoclonal antibody, may be of particular benefit in this group of patients (Wingerchuk, 2006).

Treating optic neuritis with high-dose intravenous (IV) corticosteroids reduces the risk of developing MS over the following 2 years (Beck et al., 1992). In the long term, however, this acute treatment is unlikely to affect the likelihood of progression to MS. In addition, IV corticosteroid treatment may hasten visual recovery, particularly for visual fields and contrast sensitivity, but does not significantly affect long-term visual outcomes. Because low-dose oral corticosteroids may be associated with an increased risk of recurrence of optic neuritis, this therapy should be avoided (Beck et al., 1992). In addition to IV corticosteroids, recent studies support the early use of immunomodulating treatments for high-risk patients to reduce the likelihood of progression to MS within 2 to 5 years (Balcer, 2006).

Ischemic Optic Neuropathy

Arteritic anterior ischemic optic neuropathy (AAION) is usually related to giant cell arteritis (GCA), also referred to as temporal arteritis. Its incidence increases with age, with most patients being older than 70.

GCA typically affects the extracranial medium- to large-caliber arteries, because they possess elastic lamina, which is the initial site of inflammation in this disorder (Salvarani et al., 2008). The condition is associated with polymyalgia rheumatica, consisting of proximal muscle ache, arthralgia, and stiffness, as well as with jaw claudication, fever, malaise, and scalp tenderness. The diagnosis is suggested by an elevated erythrocyte sedimentation rate and C-reactive protein and is confirmed by evidence of giant cells and endovascular inflammation on temporal artery biopsy. Acute vision loss is the presenting symptom in 7% to 60% of cases and is generally more severe than in NAION. In approximately 25% of cases, vision is limited to hand motion perception or worse (Balcer et al., 2003). In suspected cases, treatment with corticosteroids should not be delayed until a biopsy is obtained. Intraveous corticosteroids may help delay the progression of visual loss and decrease the likelihood of fellow eye involvement. The prognosis for recovery in the affected eye, however, is poor despite treatment (Hall and Balcer, 2004).

The optic disc in AAION typically has a chalky-white edematous appearance, and disc hemorrhages are likely to be present (Fig. 15.8). Coexisting retinal ischemia with cotton-wool spots is very typical for AAION. Fluorescein angiography reveals choroidal hypoperfusion (Fig. 15.9). Occasionally, GCA can be limited to the retro-orbital nerve and present without disc swelling; this situation is termed arteritic posterior ischemic optic neuropathy (PION).

Fig. 15.8 Fundus photograph of the right eye in a patient with ischemic optic neuropathy from temporal arteritis. Note blurring of the nasal disc margin, with pallor and swelling of the nerve head (black arrow). The patient also has inner retinal ischemia evidenced by large cotton-wool spots (black asterisks).

(Reprinted with permission from Prasad et al., 2010.)

Fig. 15.9 Late-phase fluorescein angiography of the left eye in a patient with giant cell arteritis, revealing nonperfused choroid (black asterisks) consistent with occlusion of posterior ciliary vessels.

(Reprinted with permission from Prasad et al., 2010.)

Nonarteritic AION is the most common cause of unilateral optic nerve swelling in adults older than 50 and is commonly associated with vascular risk factors such as diabetes or hypertension (Fontal et al., 2007). Other risk factors include a crowded optic nerve head and nocturnal hypotension, possibly precipitated by antihypertensive therapy (Arnold, 2003; Mathews, 2005). Swelling of a crowded optic nerve within the scleral canal may provoke a cycle of further vascular compression, ischemia, and swelling.

Although the clinical profile of NAION may occasionally overlap with the findings of optic neuritis (Rizzo et al., 1991), typical features of NAION include nerve fiber hemorrhages, altitudinal visual field loss, moderate to severe disc edema, and the absence of pain (Figs. 15.10 and 15.11). Because the optic nerve head is supplied by an end-arterial system of short posterior ciliary arteries and the circle of Zinn-Haller, sectoral ischemic disc swelling is common. NAION may follow ocular surgery, because an associated increase in intraocular pressure may compromise optic nerve head perfusion (Fontal et al., 2007).

Fig. 15.10 Fundus photographs in a patient with acute nonarteritic ischemic optic neuropathy in the right eye, demonstrating peripapillary edema (black arrows) with a small cup-to-disc ratio in the left eye (white arrow), suggesting a “disc at risk.”

(Reprinted with permission from Prasad et al., 2010.)

Fig. 15.11 Fundus photographs of the right eye in a patient with right nonarteritic anterior ischemic optic neuropathy. Note blurring of the disc margin and swelling of the optic nerve head (black arrows), splinter hemorrhages (white arrows), as well as dilated capillaries and luxury perfusion of the nerve head (asterisk).

(Reprinted with permission from Prasad et al., 2010.)

Many patients with NAION will have a stable deficit, although one minority may experience visual loss progressing over one month. Spontaneous improvement may occur in the first 6 months, although in many patients this reflects improved ability with eccentric fixation (Hayreh and Zimmerman, 2008). In 30% to 40% of patients, subsequent involvement of the fellow eye also occurs, and this rate is increased by the presence of vascular risk factors. When the second eye is affected in AION, optic atrophy has already developed in one eye, and acute disc edema occurs in the fellow eye; this clinical presentation is called the pseudo–Foster Kennedy syndrome. (A true Foster Kennedy syndrome is produced by optic atrophy due to compression, typically from an expanding tumor, and papilledema in the fellow eye secondary to increased ICP.) Occasionally, premonitory disc swelling in an asymptomatic eye will be noted, which may progress to frank visual loss or remit spontaneously (Hayreh and Zimmerman, 2007). Recurrence of NAION in an affected eye, however, is rare, possibly because optic nerve atrophy following the initial event decompresses the nerve. There does not appear to be a significantly higher rate of stroke in patients with nonarteritic ischemic optic neuropathy, suggesting that its pathophysiology may differ from simple vasoocclusion (Arnold and Levin, 2002).

Other Causes

Inflammatory conditions are an important cause of subacute optic neuropathy. Optic discs may appear swollen or normal, the latter indicating retrobulbar involvement. Optic nerve involvement is common in neurosarcoidosis, which can be accompanied by anterior uveitis or posterior segment vitritis (Prasad et al., 2008) (Fig. 15.12). Visual loss due to this condition is often steroid responsive. Optic neuropathy and retinal involvement may also occur with other inflammatory disorders, such as systemic lupus erythematosus and Sjögren disease (Fig. 15.13). Occasionally, optic nerve infiltration produces optic disc edema without affecting visual function, but more often there is a decrease in visual acuity and visual field loss.

Fig. 15.12 Coronal T1-weighted post-gadolinium MRI in a patient with left optic neuropathy from neurosarcoidosis. Note swelling and enhancement of right optic nerve (white arrow).

(Reprinted with permission from Prasad et al., 2010.)

Fig. 15.13 Optic disc pallor and multiple cotton-wool spots in a patient with systemic lupus erythematosus.

Infectious conditions are another frequent cause of optic neuropathy (March and Lessell, 1996). Neuroretinitis, in which optic neuropathy coexists with characteristic peripapillary or macular exudates, should be distinguished from acute demyelinating optic neuritis (Fig. 15.14). The initial clinical presentation of these conditions may be similar, but the characteristic macular star of neuroretinitis will appear within 1 to 2 weeks, establishing the diagnosis. The distinction is critical because neuroretinitis has no association with an increased risk of MS and may be due to cat scratch disease (Bartonella henselae), syphilis (Treponema pallidum), or Lyme disease (Borrelia burgdorferi). In most cases, Bartonella infection is self-limited and does not require treatment, but in severe cases doxycycline may be effective (Balcer et al., 2003). Other infectious causes of optic neuropathy include human immunodeficiency virus (HIV) and opportunistic infections including toxoplasmosis, cytomegalovirus, and cryptococcosis. Paranasal sinusitis or mucocele may lead to either compressive or inflammatory optic neuropathy.

Fig. 15.14 Neuroretinitis in a 6-year-old boy. Such exudates, although usually not present in optic neuritis, indicate an inflammatory cause for the disc edema.

(Reprinted with permission from Beck, R.W., Smith, C.H., 1988. Neuro-Ophthalmology: A Problem-Oriented Approach. Little, Brown, Boston.)

Paranasal sinus disease can cause a condition that mimics optic neuritis, with acute optic neuropathy and pain on eye movements, or can cause a progressive optic neuropathy resulting from compression (Rothstein et al., 1984). Consider optic neuropathy due to sinusitis and mucocele in patients who have clinical evidence of optic neuritis with seemingly atypical features, particularly elderly patients with severe sinus disease, a history of fevers, ophthalmoplegia, or progression of vision loss beyond 2 weeks.

Several compressive mass lesions cause a progressive optic neuropathy. The optic disc swells in cases of intraorbital compression, but in cases of retro-orbital compression, disc swelling only occurs if ICP is elevated. Chronic disc edema due to compressive lesions may be accompanied by optociliary shunt vessels and glistening white bodies on the disc surface (pseudodrusen from extruded axoplasm) (Fig. 15.15). Important causes of compressive optic neuropathy include neoplasm (including optic nerve sheath or skull base meningioma, pituitary adenoma, and craniopharyngioma), sinus lesions, bony processes (such as fibrous dysplasia), enlarged extraocular muscles (as in Graves disease ophthalmopathy), or aneurysms (Fig. 15.16). Meningiomas of the optic nerve sheath occur primarily in women and can cause acuity loss associated with either disc swelling or atrophy.

Fig. 15.15 Fundus photograph of the right eye in a patient with chronic disc swelling. Note blurred disc margins (black arrows) and an optociliary shunt vessel (white arrow).

(Reprinted with permission from Prasad et al., 2010.)

Fig. 15.16 Axial T1-weighted postcontrast MRI in a patient with an extensive sphenoid wing meningioma (asterisk) causing left optic nerve compression, ocular motor palsies, and proptosis.

(Reprinted with permission from Prasad et al., 2010.)

Primary optic nerve neoplasms include benign juvenile pilocytic glioma in children and (rarely) malignant glioblastoma in adults (Fig. 15.17). Juvenile pilocytic astrocytoma is often associated with neurofibromatosis type 1 and may be managed conservatively with frequent ophthalmological examination through adolescence (Listernick et al., 2007). When clinical or radiographic progression is detected, chemotherapy should be first-line therapy, followed by radiation and rarely surgery. Malignant optic nerve glioblastoma is much rarer, affects adults, and has a considerably worse prognosis (Spoor et al., 1980). Other neoplastic conditions include lymphoma, leukemia, carcinomatous meningitis, and optic nerve metastasis. Almost any form of carcinoma can metastasize to the optic nerve; breast and lung carcinomas are the most common.

Fig. 15.17 Axial fluid-attenuated inversion recovery (FLAIR) MRI in a patient with bilateral optic nerve gliomas (juvenile pilocytic astrocytomas) (white arrows). The patient had stigmata of type 1 neurofibromatosis.

(Reprinted with permission from Prasad et al., 2010.)

Optic neuropathy may occur as a delayed effect of radiation therapy. It can occur with or without disc edema and can sometimes be difficult to distinguish from tumor recurrence (Danesh-Meyer, 2008). Radiation optic neuropathy is suggested by exposure (typically 50-Gy dosage), characteristic 6- to 24-month time lag to symptoms, and accompanying radiation changes in proximal tissues. Progression occurs over weeks to months, and spontaneous recovery is rare. Corticosteroids may help by reducing edema in the affected optic nerve.

Visual loss in a patient with known or suspected cancer raises the possibility of a paraneoplastic optic neuropathy or retinopathy (Damek, 2005). In paraneoplastic optic neuropathy, evidence of other neurological dysfunction is common, and the antibody most commonly identified is directed toward collapsin response mediator protein 5 (CRMP5). Paraneoplastic retinopathies, on the other hand, include cancer-associated retinopathy (with antibodies to recoverin protein) and melanoma-associated retinopathy (with antibodies to rod ganglion cells).

Leber hereditary optic neuropathy (LHON) is a subacute, sequential, maternally inherited optic nerve disorder in which 80% to 90% of affected persons are males in the second or third decade of life (see Chapter 14) (Man et al., 2002; Newman, 2005). Although true disc edema is not present, the optic disc may appear hyperemic and mildly swollen in the acute phase; nevertheless, fluorescein angiography should confirm the absence of capillary leakage. Circumpapillary telangiectatic vessels, frequently present in the peripapillary nerve fiber layer, are an important clue to the diagnosis (Fig. 15.18). These early funduscopic changes also may be noted in presymptomatic eyes. As the condition progresses, the discs become atrophic. Because fibers mediating the pupillary light reflex may be selectively spared, the light reflex may be preserved despite significant visual loss. Genetic diagnosis of LHON is based on the identification of related mitochondrial DNA mutations (see Chapter 63). Most patients have permanent vision loss, although a minority will experience some recovery of vision. The prognosis depends upon the specific mutation harbored; patients with mtDNA mutation T14484C are more likely to have spontaneous recovery than patients with mutations G11778A or G3460A (Newman, 2005). At present, no effective treatment for this condition is available (Chinnery and Griffiths, 2005).

Fig. 15.18 Fundus photograph of the left eye in a patient with Leber hereditary optic neuropathy. Visual acuity was 20/200. Note hyperemia with appearance of slight nasal disc swelling (asterisk).

(Reprinted with permission from Prasad et al., 2010.)

Direct traumatic optic neuropathy (TON) may include nerve avulsion or transection and is easily recognized by the relevant history of injury (Sarkies, 2004) (Fig. 15.19). Fundus examination may reveal extensive intraocular hemorrhages. On the other hand, posterior indirect traumatic optic neuropathy will present with visual loss in the absence of significant fundus abnormalities; it may result from shearing forces and subsequent edema within the optic canal. Up to half of these patients may improve spontaneously (Sarkies, 2004). There is weak evidence that corticosteroid therapy may be helpful within the first 8 hours, but no other medical or surgical interventions have proven effective (Yu Wai Man and Griffiths, 2005; Yu Wai Man and Griffiths, 2007).

Fig. 15.19 Axial CT scan (bone windows) from a patient with direct left traumatic optic neuropathy due to avulsion by a BB pellet.

(Reprinted with permission from Prasad et al., 2010.)

A description of other uncommon causes of unilateral optic disc edema that occasionally can have a unilateral presentation will be discussed next.

Papilledema

The term papilledema refers specifically to optic disc swelling secondary to increased ICP. Disc swelling in papilledema results from blockage of axoplasmic flow in nerve fibers, increasing the volume of axoplasm in the optic disc (Hayreh, 1977). Although papilledema is typically bilateral, it can be asymmetrical, based on anatomical differences in the meningeal covering of the intracranial optic nerves that can lead to differences in transmitted pressure. On the basis of the chronicity and fundus appearance, papilledema can be divided into four stages: early, fully developed (acute), chronic, and atrophic. The acute phase of papilledema is strongly suggested by a mismatch between a markedly swollen disc and relatively spared optic nerve function, particularly central visual acuity. The most common visual field defects encountered in patients with early or acute papilledema are enlargement of the physiological blind spot, concentric constriction, and inferior nasal field loss. When acute papilledema is accompanied by decreased acuity (and often metamorphopsia), fluid typically extends within the retina to the macula itself.

In early papilledema, swelling is most prominent at the superior and inferior poles of the optic disc where the nerve fiber layer is thickest. With further development of papilledema, swelling encompasses the disc surface more uniformly, and the degree of disc elevation increases (Fig. 15.20). The retinal veins may distend slightly, and the disc may appear mildly hyperemic. These vascular changes result from nerve fiber swelling causing compression of capillaries and venules, leading to venous stasis and dilation, formation of microaneurysms, and finally disc and peripapillary splinter hemorrhages (see Fig. 15.20). Correspondingly, in fluorescein angiography, fluorescence may be absent during the retinal arterial phase as a result of delayed circulation caused by disc swelling. Dilated capillaries, microaneurysms, and flame-shaped hemorrhages may appear in the arteriovenous phase, and fluorescein may leak from dilated capillaries in the venous phase. Retinal cotton-wool spots may occur secondary to ischemia in the nerve fiber layer. Spontaneous venous pulsations usually are absent once the ICP exceeds 18 cm H₂O. Although papilledema typically is bilateral, it can be asymmetrical because of differences in transmitted pressure related to anatomical variation in the meningeal covering of the intracranial and intracanalicular optic nerves.

Fig. 15.20 Fundus photographs in a patient with acute papilledema. Note that swelling of the peripapillary nerve fiber layer causes an obscured view of underlying retinal vessels (black arrows). Splinter hemorrhages, which also suggest true papilledema rather than pseudopapilledema, are seen (white arrows).

(Reprinted with permission from Prasad et al., 2010.)

The disc appearance changes as papilledema becomes chronic, usually after weeks to months. The nerve fiber layer may appear pale and take on a gliotic appearance as a result of optic atrophy and astrocytic proliferation (Fig. 15.21). Hemorrhages are less prominent (and often have resolved completely). The disc takes on a “champagne cork” appearance in which small, glistening white bodies (pseudodrusen) result from extruded axoplasm after prolonged stasis. Shunt vessels due to compensatory dilation of preexisting communications between the retinal and ciliary circulation begin to appear.

Fig. 15.21 Fundus photograph of the right eye of a patient with chronic papilledema. Note pale, gliotic “champagne-cork” disc appearance, without retinal hemorrhages.

(Reprinted with permission from Prasad et al., 2010.)

If increased ICP and papilledema persist, optic nerve axons become damaged, and visual field loss develops. At this stage, optic disc swelling lessens, and pallor develops (atrophic papilledema). Finally, patients with end-stage papilledema exhibit optic nerve atrophy (disc pallor) without evidence of swelling. Chronic atrophic papilledema, unlike the acute phase, is often characterized by loss of visual acuity with severely constricted visual fields.

Papilledema due to increased ICP can be the consequence of numerous processes. An expanding mass lesion such as a brain tumor, cerebral edema due to stroke, or intracranial hemorrhage will increase ICP, particularly in a younger patient without age-related brain atrophy. Compression of the ventricular system in the posterior fossa is particularly likely to cause papilledema. Venous sinus thrombosis is another common cause, especially in pregnancy and other states of hypercoagulability. Cryptococcal meningitis is the infectious disorder most commonly associated with significant papilledema.

Pseudotumor cerebri, or idiopathic intracranial hypertension, can lead to disc swelling and progressive visual loss (Friedman, 2004). The condition is most common in obese women, but modest weight gain (by 5%-15%) even in nonobese women is a risk factor for disease. Additional risk factors are the use of tetracycline derivatives or vitamin A, and when present, these agents should be discontinued. Weight loss can be imperative in the management of pseudotumor cerebri. In the short term, treatment with acetazolamide can improve symptoms and reduce optic disc swelling. In refractory cases, optic nerve sheath fenestration or cerebrospinal fluid (CSF) shunting may be indicated.

Malignant Hypertension

A marked elevation in blood pressure may produce bilateral optic disc swelling indistinguishable from papilledema (Hayreh, 1977). Peripapillary cotton-wool spots also are a prominent feature in patients with malignant hypertension. Encephalopathic signs are common but not always present. Disc edema tends to develop at a lower blood pressure in patients with renal failure than in those without renal disease.

Diabetic Papillopathy

Diabetic papillopathy is a rare cause of bilateral (or sometimes unilateral) disc swelling in patients with type 1 diabetes (Barbera et al., 1996). This entity is distinct from typical NAION in that there is often bilateral, simultaneous optic nerve involvement. Often visual loss is minimal, with the exception of an enlarged physiological blind spot. Disc edema may be accompanied by marked capillary telangiectasias overlying the disc surface (Fig. 15.22). Neuroimaging and lumbar puncture may be necessary to distinguish this condition from papilledema. The pathogenesis is unclear but may relate to a mild impairment of blood flow causing disc swelling without infarction of the optic nerve head (as in the case of premonitory NAION). In many cases, the optic disc edema resolves without residual visual deficit.

Fig. 15.22 Diabetic papillopathy in a 17-year-old girl. Note the telangiectatic vessels on the disc surface.

(Reprinted with permission from Beck, R.W., Smith, C.H., 1988. Neuro-Ophthalmology: A Problem-Oriented Approach. Little, Brown, Boston.)

Other Causes

Anemia, hyperviscosity syndromes, pickwickian syndrome, hypotension, and severe blood loss are less common causes of bilateral optic disc swelling. The clinical setting generally provides clues to the diagnosis. In addition, any of the entities described under unilateral optic disc edema, particularly the infiltrative disorders, rarely can cause bilateral disc swelling. In children, optic neuritis commonly is bilateral and often is associated with bilateral papillitis (disc swelling). Bilateral ischemic optic neuropathies should prompt immediate evaluation for giant cell (temporal) arteritis in patients older than 55 years. Although most toxic optic neuropathies manifest with normal-appearing optic discs, disc edema is characteristic of methanol poisoning and also may occur in patients with ethambutol toxicity.

Optic Disc Drusen

Optic disc drusen, which constitute a common cause of pseudopapilledema, refer to calcium deposits within the optic nerve head. Although etiology is unclear, drusen may result from axonal degeneration from altered axoplasmic flow, particularly in the setting of a small optic canal (Auw-Haedrich et al., 2002). In children, disc drusen tend to be buried, whereas in adults, they often are visible on the disc surface (Figs. 15.23 and 15.24). The progression from buried to surface drusen in individual patients has been well documented. The prevalence of optic disc drusen is approximately 2% within the general population, and they can be bilateral in two-thirds of cases. Optic disc drusen are much more common in caucasian patients than in African Americans and may be genetic, inherited in an autosomal dominant pattern with incomplete penetrance.

Fig. 15.23 Fundus photographs in a patient with pseudopapilledema. There is a “lumpy-bumpy” disc appearance due to visible disc drusen (black arrows). Note that retinal vessels are not obscured by nerve fiber layer edema. Spontaneous venous pulsations may also indicate pseudopapilledema.

(Reprinted with permission from Prasad et al., 2010.)

Fig. 15.24 Optic disc drusen in a 50-year-old man.

(Reprinted with permission from Beck, R.W., Smith, C.H., 1988. Neuro-Ophthalmology: A Problem-Oriented Approach. Little, Brown, Boston.)

Patients with optic disc drusen generally do not complain of visual symptoms, although rarely a patient may experience transitory visual obscurations similar to those described by patients with true papilledema. Although patients may be unaware of a visual field defect, such deficits are common, occurring in approximately 70% of eyes with visible disc drusen and in 35% of those with pseudopapilledema but no visible drusen (Auw-Haedrich et al., 2002). The scotoma probably results from nerve fiber layer thinning and axonal dysfunction caused by the drusen. The visual field defects, therefore, generally follow a nerve fiber bundle distribution, most commonly affecting the inferior nasal visual field. Enlargement of the blind spot and generalized field constriction also may occur. Progression of visual field defects in the setting of drusen is well documented. In addition, visual field loss in the setting of optic disc drusen occurs secondary to hemorrhage, superimposed ischemic optic neuropathy, or an associated retinal degeneration. Visual acuity loss associated with drusen is rare, however, and should prompt an evaluation for alternative causes.

Branch Retinal Artery Occlusions and Encephalopathy (Susac Syndrome)

Branch retinal artery occlusions and encephalopathy (Susac syndrome) is a rare disorder characterized by multiple branch retinal artery occlusions and neurological dysfunction (Gross and Eliashar, 2005; Susac, 2004). Susac syndrome most commonly affects women between the ages of 20 and 40 years. A viral syndrome may precede the development of ocular and neurological signs. The most prominent neurological manifestations are impaired mentation and sensorineural hearing loss. Cerebrospinal fluid in patients with Susac syndrome shows a mild lymphocytic pleocytosis and elevated protein. Antinuclear antibody (ANA) testing and cerebral arteriography are generally normal, but brain MRI most often demonstrates multiple areas of high signal intensity that resemble demyelinating plaques on T2-weighted images.

Ocular Ischemic Syndrome

Generalized ocular ischemia indicates involvement of both retinal and ciliary circulations in the eye. Signs of optic nerve and retinal ischemia may be present, as well as ophthalmoplegia and evidence of anterior segment ischemia (iris atrophy, loss of pupil reactivity, cataract formation, rubeosis iridis). Carotid artery occlusion or dissection and giant cell arteritis are the primary considerations in patients with ocular ischemia.