Diagnostic Approach to Vision Loss

Abstract

Purpose of Review:

This review emphasizes the differential diagnosis of visual loss for the neurologist.

Recent Findings:

As an expert on the CNS, of which the eye is a part, the neurologist is expected to be able to evaluate a patient’s report of visual loss and provide at least a cursory examination of the ocular apparatus and visual pathways. To appropriately localize the lesion within the eye and to generate a diagnosis, the neurologist must at least be aware of the other clinical entities that can cause visual loss, especially sudden visual loss, other than optic nerve damage. Once the problem has been localized to the optic nerve, a complete differential diagnosis will include all the pathophysiologic processes that can affect any tissue, specifically any piece of brain tissue. Intracerebral visual loss from damage to the chiasm or retrochiasmal pathways or to the downstream centers of higher visual processing is also common, given that the visual pathways constitute more than one-third of the supratentorial brain mass and are frequently affected by structural lesions and a wide range of neurologic disorders. The paucity of neuro-ophthalmologists makes it essential for neurologists to feel comfortable evaluating and managing patients with visual loss from presumed optic neuropathies or lesions of the intracranial visual pathways.

Summary:

The diagnosis of visual loss is not always easy, even for ophthalmologists. Good collaboration between neurologists and ophthalmologists is the key to a correct diagnosis and appropriate management when a neuro-ophthalmologist is not readily available.

INTRODUCTION

The neurologist is frequently confronted with a patient reporting visual loss. On some occasions, the patient has already been seen by an ophthalmologist (MD) or, more often, an optometrist (OD). It is not unusual, however, for the neurologist to be the first health care provider to examine the patient. As an expert on the CNS, of which the eye is a part, the neurologist is expected to be able to evaluate a patient’s report of visual loss and provide at least a cursory examination of the ocular apparatus and visual pathways.

Neurologists should be able to recognize when visual loss is caused by an optic nerve problem and know the classic defining features of an optic neuropathy. If these characteristics are not present, other abnormalities involving the ocular media and the retina should be considered. To appropriately localize the lesion within the eye and to generate a diagnosis, neurologists must at least be aware of the other clinical entities that can cause visual loss, especially sudden visual loss, other than optic nerve damage. No one realistically expects the neurologist to be an expert on the eye. However, certain red flags on clinical evaluation should make the neurologist think about other diagnoses and seek prompt ophthalmic referral.

Once the neurologist has localized the problem to the optic nerve, a complete differential diagnosis will include all the pathophysiologic processes that can affect any tissue, specifically any piece of brain tissue. Intracerebral visual loss from damage to the chiasm or retrochiasmal pathways or to the downstream centers of higher visual processing is also common, given that the visual pathways constitute more than one-third of the supratentorial brain mass and are frequently affected by structural lesions and a wide range of neurologic disorders.1,2,3

GENERAL APPROACH TO THE PATIENT WITH VISUAL LOSS

History

Any patient with recent visual loss should be evaluated promptly, as some of the causes of visual loss represent medical emergencies with implications for treatment. A good history is of paramount importance. Assess whether the patient has a previous history of lazy eye or ocular trauma or family history of visual loss. Does the patient have any systemic illnesses (eg, diabetes mellitus, Marfan syndrome) or neurologic diseases (eg, multiple sclerosis, carotid stenosis) that might indicate risk for various causes of visual loss?

Patients with visual loss may report a decreased ability to see things at a distance or near, blurring of images, or loss of pieces of their visual field. To pinpoint the location, nature, and ultimately the cause of the visual problem, the most important determination is whether visual loss is in one eye or both. This is not always an easy task; it may be necessary to specifically ask whether the patient has checked by covering each eye separately (Table 1-1). Truly monocular visual loss signifies an abnormality in the eye itself or in the optic nerve anterior to the chiasm, while binocular visual loss results from either bilateral anterior lesions or, more likely, a chiasmal or retrochiasmal lesion (Figure 1-1). The next most important issue is whether the visual loss is transient or persistent. The tempo of visual loss is also important, as is the presence or absence of associated symptoms, especially pain (Table 1-2).

Table 1-1.

Neuro-ophthalmic Evaluation of the Patient Reporting Visual Loss

Table 1-2.

Causes of Monocular Visual Loss (Persistent or Transient) Associated With Pain

Figure 1-1.

Diagram showing the effects on the field of vision produced by lesions at various points along the visual pathways. Lesions anterior to the chiasm produce ipsilateral, monocular visual loss, while lesions at the level of, or behind, the chiasm produce bilateral visual field defects with respect of the vertical meridian.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Examination

When examining the patient with a report of visual loss, each eye must be tested separately. The first step is to determine whether visual loss is present and assess whether it is simply refractive (ie, that the patient only needs a new set of glasses). The best means of determining whether visual loss is present is measurement of the patient’s visual acuity. It is the only sensory function that can be truly quantitated with minimal equipment; yet, paradoxically, it is one of the elements of a complete neurologic examination that is often omitted, even when the patient has visual symptoms. The best method is a well-illuminated distance chart at the appropriate distance, but a near card (also at the appropriate distance of 14 inches) can be used. The patient should wear his or her spectacle correction. If a near card is used, reading glasses must be worn if the patient is in the presbyopic age group (beginning in the forties). Test each eye individually and ask the patient to read the smallest line he or she can. Unless you encourage them, many patients give up too soon and lead you to the false conclusion that they have subnormal vision. If the acuity is less than 20/20, you need to know if refractive error is responsible, since uncorrected visual acuity is generally not the neurologist’s domain. Although the neurologist does not manipulate lenses, an easy “shortcut,” ie, a pinhole, may be used. If an uncorrected refractive error is the cause of subnormal visual acuity, the patient’s vision should improve by looking through a pinhole (which can be placed over the patient’s glasses if necessary).

Early optic nerve disease may manifest as a reduction in saturation or brightness of colors. Pseudoisochromatic color plates are used to test color vision, which is abnormal in both eyes of patients with congenital color blindness (usually males) and in one eye of patients with unilateral optic nerve dysfunction. A less-sophisticated but valid test of color involves bringing a bright red object before each eye, and asking the patient to estimate the amount of desaturation of the color in one eye as compared to the other.

Visual fields testing, at least by the confrontation method, should be performed on every patient. The overlap in binocular fields may mask monocular field defects; therefore, monocular testing is necessary. Maintaining central fixation, the patient is instructed to look at the examiner’s opposite eye or nose and count fingers presented within the central 30 degrees. The patient must perform the task equally well in all four quadrants of the horizontal and vertical axes. Then the patient is directed to count fingers in two quadrants simultaneously. If the patient consistently ignores a quadrant of the visual field, a subtle field defect is present. A consistent difference in color perception across the horizontal or vertical meridian may be the only sign of an altitudinal or hemianopic defect, respectively. An abrupt change across the horizontal axis in one eye suggests optic nerve disease, and an abrupt change across the vertical meridian in both eyes indicates visual loss of intracranial origin. The more peripheral visual field can be screened by using finger movements. The sensitivity and accuracy of confrontation visual fields may be enhanced by using a laser pointer on a blank wall as a static and kinetic target.

Formal visual field testing provides a more standardized examination, may reveal more subtle abnormalities, and can quantify the defects in order to follow disease progression. Tangent screen testing plots the patient’s central 30 degrees of vision, is easy to perform and inexpensive, but may no longer be as available in neurologists’ or even ophthalmologists’ offices. Two other types of visual field testing are usually found in the offices of ophthalmologists and neuro-ophthalmologists. Kinetic (Goldmann) perimetry testing (Figure 1-2) can quickly establish the pattern of visual field loss in ill, poorly attentive, or elderly patients who need continued encouragement to maintain fixation and respond appropriately. The Goldmann perimetry test charts the entire visual field, including the temporal crescent. The quality of the field is examiner dependent, however, and the availability of these perimeters and specially trained perimetrists is diminishing. Another method of assessing the visual field is the automated static perimetry test (Figure 1-3). This more time-consuming method requires good patient cooperation and attention but is more sensitive, quantitative, and reproducible. Assuming the patient is capable of performing the test adequately, automated perimetry is the technique of choice in following patients with optic nerve lesions, papilledema, chiasmal compressive lesions, and other progressive visual disorders. Interpretation of automated visual fields is not as intuitive as with kinetic perimetry and requires familiarity with the computerized program and its method of data presentation (Figure 1-3).

Figure 1-2.

Normal Goldmann visual field. The left eye is shown on the left and the right eye is shown on the right. The physiologic blind spot is located temporally in each eye.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-3.

Normal Humphrey visual field (Swedish Interactive Threshold Algorithm [SITA] Fast 24-2). Only the right eye is shown. Interpretation of automated perimetry: Since it is rare for clinically significant visual field defects to present only with visual loss outside 30 degrees, most automated perimetry programs assess the central 30 degrees or 24 degrees of vision (the central visual field). The vertical and horizontal midlines are essential areas. Automated perimetry uses computerized programs to randomly test points in the patient’s central visual field with a standard stimulus size but varying stimulus intensities. The most commonly used method of testing is the threshold strategy, in which the stimulus intensity is varied and presented multiple times at each location so that the level of detection of the dimmest stimulus is determined. This is then reported on a computerized printout in various ways, some numeric, others pictorial. To accurately interpret the automated perimetry printout, the clinician must first assess the quality of the visual field. The ability of the patient to perform the test can be evaluated by measurements of reliability reported on the printout. In the example provided here, the right eye was tested (as indicated by the word “RIGHT” in the right upper corner). Reliability measurements are reported in the upper left corner, and include the number of fixation losses (2/10), false-positive (8%), and false-negative errors (0%) during the test. The numeric grid just to the right of the measurements of reliability is a presentation of the threshold levels in decibels for all points checked in the patient’s visual field. A recorded number of zero indicates that the patient could not detect even the brightest stimulus at that point. The higher the number, the better the vision at that point in the field. These numbers are then converted to a grayscale representation of the field (upper right), which provides a gross picture of the size and severity of the field defects present. A comparative scale on the bottom relates the degree of grayness on the grayscale to the change in decibel levels from the numeric grid. The number scale labeled “Total Deviation” indicates the amount each point deviates from the age-adjusted normal values. In this case, the more negative a number, the more abnormal that point. The number scale to the right labeled “Pattern Deviation” highlights localized abnormalities in the visual field, helping to emphasize the pattern of visual field loss. The mean deviation (MD) is −2.89 dB and the foveal sensitivity is 39 dB.

The pupils should be examined for size, shape, and reactivity to light and near. The most important part of the pupil evaluation of the patient with visual loss is the search for a so-called Marcus Gunn or swinging flashlight sign, evidence of a relative afferent pupillary defect. Normally, when light is directed into either eye, both pupils react equally. The brighter the light source, the greater the degree of bilateral pupillary constriction. The amount of pupillary constriction to the same light source directed to either eye should be identical. If there is unilateral optic nerve (or retinal ganglion cell) dysfunction, the light signal received by the brainstem efferent centers will be relatively less when the light is shown in the damaged eye than when the same light source is presented to the unaffected eye. Hence, both pupils will constrict less when the involved eye is stimulated, and more when the normal eye is stimulated. Swinging the light source back and forth emphasizes this difference in transmission of the afferent signal, since both pupils will reset at the size appropriate for the amount of light transmitted by the illuminated optic nerve. When the light source swings from the affected eye to the unaffected eye, further constriction of both pupils will be demonstrated; when the light swings back to the involved eye, relative dilation of both pupils will occur. Even though the examiner may only look at the pupil upon which the light is shining, it is important to be aware that both pupils are changing size equally during this maneuver. By placing neutral density filters over the normal eye, the examiner can neutralize the relative afferent defect and quantitate its severity. Ocular disease, such as corneal abnormalities, cataracts, and most retinal disorders, do not cause a relative afferent pupillary defect. Exceptions include central or large-branch retinal artery occlusions and large retinal detachments. When a relative afferent pupillary defect is demonstrated, the cause is generally unilateral or asymmetric optic nerve dysfunction.

The ocular examination is typically within the ophthalmologist’s domain; however, a careful penlight examination may reveal corneal or lens abnormalities that could be the cause of diminished vision or the source of obstruction of an adequate view of the fundus. Abnormalities of the ocular media (eg, cornea or lens) sufficient to cause significant visual loss usually result in a poor view of the ocular fundus. Hence the saying, “If you can’t see in, the patient can’t see out.” Abnormalities of the cornea and lens may become apparent if the direct ophthalmoscope is set at a high plus lens setting (black or green numbers on the ophthalmoscope) and the examiner stands back from the patient. External examination may demonstrate evidence of an underlying disease. For example, injection over the extraocular muscle insertions can signify thyroid ophthalmopathy, and arterialization of the conjunctival vessels may suggest arteriovenous shunting, usually at the level of the cavernous sinus (Figure 1-4).

Figure 1-4.

External view of the right eye of a patient with a direct carotid-cavernous fistula. The conjunctival vessels are arterialized in the right eye as a result of the arteriovenous shunting.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Ophthalmoscopic examination is an essential component of the neurologic examination. Actually seeing the fundus is a necessary first step and not always an easy task in the office or at the bedside. Common obstacles to obtaining an adequate view of the fundus include too small a pupil, suboptimal use of available equipment, and media opacities (which may be the cause of visual loss in that patient).

Every neurologist should have easy access to dilating drops and feel comfortable using them. All dilating drop bottles have red caps. Typically, one instills a short-acting parasympathetic antagonist, such as tropicamide 1%, and a short-acting sympathomimetic, such as phenylephrine 2.5%. Dilation occurs after initial instillation within 20 to 30 minutes and usually recovers within 4 to 6 hours. The drops may sting initially and the ensuing pupillary dilation and cycloplegia may cause photophobia, glare, and accommodative difficulties.

In our practice, the only relative contraindication to dilation is the neurology or neurosurgery intensive care unit (ICU) patient with a fluctuating or precarious neurologic status. Communication with nursing and physician staff (as well as the patient and family) will help avoid any unnecessary panic when large, nonreactive pupils are discovered. Always dilate both pupils, as a unilateral, dilated, nonreactive pupil is particularly fear provoking.

A frequently voiced concern is that of inducing glaucoma with the use of dilating drops. Most patients with glaucoma have chronic open-angle glaucoma, a disease of chronic raised intraocular pressure that is not induced or worsened by the use of dilating drops. No contraindication to using dilating drops in patients with chronic open-angle glaucoma exists. Dilating drops may cause acute angle-closure glaucoma, an entity related to chronic open-angle glaucoma exists only inasmuch as both conditions manifest elevated intraocular pressure. In patients with a narrow angle between the iris and the cornea (ie, a shallow anterior chamber), a dilating pupil may cause a blockage of the normal outflow of aqueous humor and an acute elevation of intraocular pressure. This may cause pain, blurred vision, halos around lights, nausea, redness of the eye, and clouding of the cornea. Acute angle-closure glaucoma after pupillary dilation is extremely rare, and such patients should immediately be sent to an ophthalmologist.

The direct ophthalmoscope will give an excellent two-dimensional view of the posterior pole, specifically the optic disc, the macular region, and the vessels of the major arcades. Neurology is a very disc-o-centric specialty, but every neurologist should get into the habit of moving temporally to also get a good look at the macula. The single most common mistake in the use of the direct ophthalmoscope when viewing the fundus is failure to get close enough to the ophthalmoscope and to the patient. Examiner glasses can be removed, and the examiner’s hand holding the ophthalmoscope should be touching the patient’s cheek. By changing the focus in and out, one can estimate the relative depth and elevation of fundus features, such as the optic cup or the optic disc. The green light (red-free filter) can be used to see details of the nerve fiber layer. If the examination must be performed in an undilated patient, place the ophthalmoscope as close to the eye as possible, have the patient fixate on a distant target (to minimize the miosis resulting from accommodation), and dim the room lights.

Peripheral retinal findings may provide diagnostic clues, but, most often, disease of the optic nerve or the most central retina (the macula) causes central visual function loss. Pertinent findings include disc edema or disc atrophy; whitening of the inner retinal layers secondary to infarction, as in central and branch retinal artery occlusions; hemorrhages and venous dilation in central retinal vein occlusion; detachment of the retina or accumulation of subretinal fluid as in central serous retinopathy; or degeneration of the retina as in age-related macular degeneration. Transient visual loss is often caused by abnormalities of the retinal vasculature, eg, intraluminal particulate matter, such as calcific or platelet fibrin emboli from the heart (Figure 1-5), or refractile cholesterol emboli (Figure 1-6) from the carotid arteries or aortic arch. Infections, such as syphilis, or systemic inflammatory disorders, such as sarcoidosis, may cause vasculitis with arterial or venous sheathing and exudate deposition (Figure 1-7).

Figure 1-5.

Funduscopic examination of the right eye of a patient with acute visual loss. A white embolus (fibrin from a cardiac thrombus) can be seen in the inferior branch of the central retinal artery associated with whitening of the corresponding retina (branch retinal artery occlusion).

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-6.

Asymptomatic cholesterol emboli in the retinal arterioles in a patient with carotid and aortic arch atheroma.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-7.

Neurosarcoidosis with right optic nerve head swelling, retinal vasculitis, and retinal hemorrhages.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Other techniques of ocular and funduscopic examination are not readily available to the neurologist, and referral to an ophthalmologist may be appropriate. Slit-lamp biomicroscopy provides a three-dimensional, cross-sectional, magnified view of the cornea, anterior chamber, lens, and vitreous. Abnormalities of the media are readily clarified and localized in-depth. Slit-lamp examination with a 90-diopter, 60-diopter, or ruby lens allows for a three-dimensional view of the posterior pole. Similarly, indirect ophthalmoscopy with a 20-diopter lens gives a three-dimensional view of the fundus, with a wider view, including the peripheral retina. Fundus photography may allow for more leisurely study of optic disc and retina details. With modern digital technology, fundus photography is obtainable in patients without pupillary dilation, even in acute nonophthalmology settings, such as emergency departments and even neurologists’ offices. Fluorescein angiography has the added advantage of providing information regarding the functional vascular status of the retina. Optical coherence tomography (OCT) has the advantage of providing two-dimensional cross-sectional anatomic views of the layers of the retina, including the nerve fiber layer.

TRANSIENT MONOCULAR VISUAL LOSS

Transient monocular visual loss most often results from transient ocular ischemia (so-called amaurosis fugax) but may also result from other mechanisms such as disc edema or numerous ocular diseases (Table 1-2).

Patients with vascular transient monocular visual loss generally report acute monocular vision loss, either partial or complete, lasting a few minutes. The most common ophthalmic symptom of carotid occlusive disease, transient monocular visual loss is caused by lesions of the common or internal carotid arteries embolizing material to the retinal circulation. Less commonly, severe stenosis of the carotid circulation causes transient visual loss due to retinal or choroidal hypoperfusion. Vascular transient monocular visual loss is clearly a marker of systemic vascular disease and should prompt immediate comprehensive patient evaluation similar to that of cerebral ischemia, including for symptoms and signs of giant cell arteritis.

In another clinical scenario, the transient monocular visual loss lasts only seconds and is precipitated by changes in posture, such as bending over. These transient visual obscurations are characterized by brief blackouts or grayouts of vision and often indicate underlying optic disc edema or disc anomalies that cause high tissue pressure at the optic nerve head. Transient visual obscurations may be the only symptom of elevated intracranial pressure (ICP), which is their most likely cause (Case 1-1). Disc edema results from a variety of disorders; however, the term papilledema is reserved for disc edema secondary to elevated ICP (Figure 1-9). Papilledema is classically bilateral, although it can be asymmetric, and the associated transient visual obscurations may involve only one eye. In contrast to the persistent central visual loss encountered in most causes of disc edema, visual acuity is typically normal in patients with papilledema. Neurologic examination may be normal with the exception of the ophthalmoscopic appearance of elevated optic nerve heads, blurring of the distinct disc borders, obscuration of the disc vessels, disc hyperemia, and venous engorgement. Visual fields may be normal or show nerve fiber bundle defects, enlarged blind spots, or generalized constriction. The recognition of papilledema warrants immediate neuroimaging, MRI if available, to evaluate the patient for cerebral mass lesions, hydrocephalus, or venous sinus thrombosis. If neuroimaging demonstrates no abnormalities, a lumbar puncture should be performed to confirm the presence of elevated ICP and to analyze the CSF for evidence of meningeal inflammation.

Figure 1-9.

Severe bilateral papilledema in a patient with hydrocephalus and raised intracranial pressure. The disc margins are blurred, the veins are dilated, and the vessels are obscured by the edema. Numerous exudates and hemorrhages are present. The right eye is shown on the left and the left eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Case 1-1

A 22-year-old woman reported severe headaches and blackouts of vision. Her past medical history was remarkable for obesity. She began to experience chronic diffuse headaches approximately 1 month prior and transient visual obscurations in both eyes 2 weeks before her initial presentation to an ophthalmologist, who found normal visual acuity with bilateral disc edema. MRI of the brain was normal. A lumbar puncture showed an opening pressure of greater than 500 mm of CSF, no cells, and normal protein and glucose contents. She was diagnosed as having idiopathic intracranial hypertension and was treated with acetazolamide, a total of 1500 mg/d in divided doses. Her headaches improved and no formal visual fields were performed. Two months later, she started to bump into doors and had a minor motor vehicle accident, and she presented the next day for a neuro-ophthalmic evaluation.

On examination she was obese. Visual acuity was 20/30 right eye and 20/50 left eye. She correctly identified 14 of 14 color plates with the right eye and 10 of 14 color plates with the left eye. A left relative afferent pupillary defect was present. Motility was full. Ophthalmoscopic examination revealed bilateral disc edema (Figure 1-8A). Automated perimetry demonstrated severe constriction of the visual fields in both eyes, the left worse than the right (Figure 1-8B). The remainder of her neurologic examination was normal.

Figure 1-8.

Severe papilledema with visual field loss in idiopathic intracranial hypertension. A, Severe chronic bilateral optic nerve edema consistent with papilledema from raised intracranial pressure. The optic nerves are elevated with peripapillary hemorrhages and retinal exudates. The veins are dilated. Optic nerve pallor consistent with secondary optic nerve atrophy from untreated chronic papilledema is present. The right eye is shown on the left, and the left eye is shown on the right. B, Constricted visual fields shown on a Humphrey 24-2 visual field (the dark parts are not seen). The left eye is shown on the left and the right eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Comment. The patient was correctly diagnosed with idiopathic intracranial hypertension. Unfortunately, her initial management was directed only at her symptoms and neglected to consider the effect of chronic papilledema on her visual function. By the time the appropriate examination of visual fields was performed, she had experienced severe field loss and some loss of visual acuity. Because of the severity of visual field loss despite maximally tolerated medical therapy, surgical treatment was determined necessary. At the time of evaluation, her visual function was altered and she had only mild headaches. Therefore, the patient underwent an optic nerve sheath fenestration in the left eye. One month later, visual acuity was 20/25 right eye and 20/50 left eye. Color vision was 14/14 right eye and 13/14 left eye. The visual field was much improved in the left eye, and mildly improved in the right eye. Motility was full. Ophthalmoscopic examination demonstrated resolution of disc edema with residual optic atrophy, the left eye being worse than the right. In this case, the optic nerve sheath fenestration improved visual function in both eyes, presumably by decreasing intracranial pressure. On long-term follow-up, her examination remained stable and she had no complaint of headache or diplopia.

Additional causes of transient monocular visual loss include recurrent angle-closure glaucoma, disc anomalies such as drusen (Figure 1-10), and orbital tumors. Transient worsening of vision may also occur with exposure to heat or with exercise in patients with underlying demyelinating optic neuropathies (Uhthoff phenomenon). These disorders should ordinarily be identifiable by their typical presentations, the associated symptoms and signs, and the funduscopic appearance.

Figure 1-10.

Bilateral optic nerve drusen. Round, globular, whitish-yellow hyaline bodies are present in the optic nerve head. The right eye is shown on the left and the left eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

PERSISTENT MONOCULAR VISUAL LOSS

Persistent monocular visual loss must localize to the eye itself or the optic nerve anterior to its junction with the chiasm. In order to make this distinction, the neurologist must be knowledgeable of the classic features of a unilateral optic neuropathy: (1) central visual loss, (2) clear view through the ocular media to the optic nerve, (3) a relative afferent pupillary defect, and (4) a swollen or pale optic nerve head. If all these features are present, little question exists as to the localization of the lesion. Of course, it is not always so clear-cut. Some optic neuropathies may spare central visual acuity. In up to 50% of patients with nonarteritic anterior ischemic optic neuropathy, for example, visual acuity is good despite altitudinal visual field loss. In other acute optic neuropathies, such as most cases of retrobulbar idiopathic optic neuritis, the optic nerve appears normal for at least 4 to 6 weeks before optic nerve head pallor ensues. However, as in the examples shown in Case 1-2 and Case 1-3, the presence of other features, especially a relative afferent pupillary defect, facilitates recognition of the optic nerve as the locus of pathology.

Case 1-2

A 33-year-old woman was referred for an 8-day history of progressive decreased vision in her left eye. One day prior to the onset of visual loss, she had experienced pain over her left forehead that worsened with eye movements. Her past medical history was unremarkable, and she was on no medication.

On examination, visual function was normal in the right eye. In the left eye, visual acuity was 20/400 with no color perception and a dense relative afferent pupillary defect. Visual field testing showed a large dense central scotoma. Motility was full. The fundi were normal (Figure 1-11), as was the remainder of the examination. It was felt that the most likely diagnosis was idiopathic retrobulbar optic neuritis. MRI of the brain and orbits showed scattered T2 white matter abnormalities and enhancement of the left optic nerve (Figure 1-12).

Figure 1-11.

Normal-appearing optic nerves; they are symmetrically pink and no disc edema is present. The right eye is shown on the left and the left eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-12.

MRI of the brain and orbits showing scattered multifocal hyperintense lesions in the periventricular white matter (A, axial fluid-attenuated inversion recovery [FLAIR] image) and enhancement of the left optic nerve (B, axial T1-weighted image with gadolinium and fat suppression).

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

At 2-month follow-up, vision in the left eye was much improved, and her visual field was now normal. The left optic disc was pale temporally (Figure 1-13). The patient elected to begin immunomodulating therapy to delay or reduce the subsequent risk of clinically definite multiple sclerosis.

Figure 1-13.

Temporal pallor of the left optic nerve 2 months after visual loss. The left optic nerve is shown on the right and the right optic nerve is shown on the left.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Comment. This patient’s symptoms followed the typical course of retrobulbar optic neuritis. The MRI documented the presence of white matter lesions, and although she never had any other neurologic symptoms, she was at high risk for the subsequent development of multiple sclerosis.

She decided against IV steroid therapy, but interferon therapy was initiated in an effort to delay subsequent neurologic dysfunction. She remained at risk for development of multiple sclerosis as well as for recurrence of optic neuritis.

Case 1-3

A 37-year-old woman presented with visual loss in the right eye. Her past medical history was unremarkable, and she was on no medication. Five weeks prior to presentation, she had reported irritation and itchiness of the right eye, which improved with artificial tears. Five days later, she had noticed decreased vision in the inferior visual field in the right eye, which worsened over 4 to 5 days. She had no eye pain, pain with eye movement, or headaches. She denied any neurologic symptoms. She had a brain MRI that showed no optic nerve enhancement, but showed one small nonenhancing periventricular T2 high signal lesion. She was diagnosed with a right optic neuropathy by her optometrist, presumably related to a right optic neuritis. She did not receive treatment. Her vision failed to improve during the following 4 weeks.

On neuro-ophthalmic examination, visual acuity was 20/20 in both eyes and color vision was normal, but mild red desaturation was present in the right eye. Orbits, slit-lamp examination, and intraocular pressures were normal. A right relative afferent pupillary defect was present. Eye movements and eyelids were normal. Humphrey visual fields showed an inferior arcuate defect in the right eye. Funduscopic examination showed mild disc edema in the right eye with a small cup-disc ratio in both eyes (Figure 1-14).

Figure 1-14.

Mild optic nerve edema on the right with a small cup-disc ratio in both eyes, consistent with a “disc at risk” for anterior ischemic optic neuropathy. Note the subtle superior pallor of the right optic nerve. The right eye is shown on the left and the left eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Comment. This patient had an anterior right optic neuropathy (ie, decreased visual acuity, red desaturation, visual field defect, ipsilateral relative afferent pupillary defect, and mild disc edema). The absence of pain, the absence of optic nerve enhancement on the MRI, and the absence of spontaneous recovery of vision argued against an optic neuritis as the cause of her optic neuropathy. The mild disc edema in the setting of a small cup-disc ratio was very suggestive of a nonarteritic anterior ischemic optic neuropathy despite her young age and absence of known vascular risk factors. An accurate diagnosis was crucial because a false diagnosis of optic neuritis would have likely resulted in a number of costly tests (eg, lumbar puncture and repeat MRI) and a possible wrong diagnosis of presumed high risk for the development of multiple sclerosis given the finding of an incidental small white matter T2 hyperintensity on her brain MRI.

Many causes of visual loss are not optic neuropathies, and the neurologist should be familiar with these causes. Clinical entities that cause visual loss and fail to allow a clear view back to the fundus almost always suggest problems with the ocular media, ie, the cornea, the anterior chamber, the lens, or the vitreous. Many of these problems can be recognized with penlight observation or use of the direct ophthalmoscope focused on the more anterior eye (ie, with more plus diopters dialed in). Corneal surface changes, scarring, edema (such as seen in acute angle-closure glaucoma), or structural abnormalities (such as keratoconus) will make the view into the eye difficult. A hyphema (blood in the anterior chamber) may be visible to the naked eye. Cataracts will cause blurring, darkening, or an orange-brown discoloration of the fundus details, a glaring reflection of the ophthalmoscope’s light, or complete obscuration of view. Vitreous hemorrhage (such as with diabetic retinopathy or Terson syndrome after subarachnoid hemorrhage), inflammation (uveitis), or debris may also completely obscure or blur the view of the optic nerve and retina.

The most common difficulty faced by the neurologist in the differential diagnosis of persistent monocular visual loss is deciding whether the visual loss is the result of a lesion of the optic nerve or a lesion of the macula. Both optic nerve lesions and macular lesions can reduce central acuity, and both can cause central scotomas on visual fields. Both may also affect color vision, although the amount of color vision deficit for any given visual acuity deficit is usually greater for an optic neuropathy than a maculopathy. Maculopathies are rarely painful, as opposed to some causes of optic neuropathy, especially idiopathic optic neuritis in which pain, particularly pain exacerbated by eye movement, is a common feature. Classically, maculopathies cause visual distortions and vision is slow to recover after bright light, features not usually found among optic neuropathies. If the macula definitely looks abnormal, the answer is clear, but some retinal lesions are quite subtle and difficult to detect. However, it is the absence of the relative afferent pupillary defect that should lead the examiner to suspect a problem not involving the optic nerve.

Central serous retinopathy is a relatively common cause of visual loss that occurs when serous fluid accumulates in the subretinal space underneath the macula, causing a relative detachment of the layers of the retina. It makes the macula look like a blister (Figure 1-15). Presumably fluid has leaked from the choroid through a break in the retinal pigment epithelium. It occurs preferentially in males (male-to-female ratio of 10:1) in their fourth and fifth decades of life. The symptoms are fairly sudden in onset and consist of painless blurred and dim central vision and usually metamorphopsia. Most eyes improve spontaneously within 1 to 6 months. The clinical picture may be mistaken for optic neuritis, but male sex, metamorphopsia, lack of pain, and the usual absence of a relative afferent pupillary defect should raise suspicion for central serous retinopathy.

Figure 1-15.

Central serous retinopathy in the left eye. The macula appears elevated, like a blister.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Macular degeneration is typically a progressive, bilateral acquired degeneration of the outer retina in the region of the macula. With age, some patients develop chronic degenerative changes, so-called age-related macular degeneration. An early sign of the process is the appearance of yellow-white deposits with irregular borders known as drusen (a completely different entity from the drusen found in optic nerves). These drusen result from thickening of the Bruch membrane or from the retinal pigment epithelial cells’ inability to remove lipofuscin and other waste products. Hypopigmentation or hyperpigmentation of the retinal pigment epithelium may also be present (Figure 1-16). There are many other causes of maculopathy, many hereditary, some toxic, but they are almost always bilateral. Some patients with macular degeneration develop choroidal neovascularization that results in subretinal hemorrhage, subretinal exudate, and profound visual loss.

Figure 1-16.

Age-related macular degeneration in the right eye. The macula is yellowish with hypopigmented and hyperpigmented areas consistent with geographic atrophy.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

A macular hole is just that. Idiopathic macular holes and cysts occur primarily in women in the sixth through eighth decades of life, probably as a result of progressive vitreoretinal traction. A fully formed hole is visible as a sharply delineated defect in the middle of the macula (Figure 1-17). The other eye may become similarly involved in up to 30% of patients.

Figure 1-17.

Macular hole in the left eye. A circular hole in the center of the macula is seen.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Acquired enlargement of the physiologic blind spot, both symptomatic and asymptomatic, is usually the result of swelling of the optic nerve head. Occasionally, however, blind spot enlargement may occur with a normal-appearing optic nerve and signify peripapillary outer retinal dysfunction, the so-called acute idiopathic blind spot enlargement syndrome. Acute idiopathic blind spot enlargement syndrome is characterized by the sudden onset of a monocular temporal blind area centered on the physiologic blind spot, often with associated photopsias in the scotomatous field. Women are affected at least twice as frequently as men, and most patients are between the ages of 20 and 40 years. Visual acuity and color vision are typically spared, and there may or may not be a relative afferent pupillary defect (present less than 50% of the time). Ophthalmoscopic and fluoroangiographic findings are often normal or consist of nonspecific pigmentary changes or subtle grayish discoloration of the peripapillary retina. The electroretinogram, especially a multifocal electroretinogram, is frequently abnormal. Acute idiopathic blind spot enlargement syndrome generally resolves over several weeks or months but occasionally will recur in the same or opposite eye.

The fibers that form the optic nerve originate in the ganglion cells, one of the innermost layers of the retina. The axons of the ganglion cells lie superficial to the ganglion cell layer and are designated as the nerve fiber layer prior to their coalescence into the optic nerve. Damage to the ganglion cell layer or the nerve fiber layer is tantamount to damage to the optic nerve; ie, visual loss, a relative afferent pupillary defect if unilateral, and ultimately optic nerve atrophy will occur. Since the central retinal arterial and venous circulations subserve the inner layers of the retina (including the ganglion cell and nerve fiber layers), retinal vascular occlusive events will result in inner retinal damage, visual loss, and a relative afferent pupillary defect.

Ophthalmic artery and central and branch retinal artery occlusions are typically acute and painless. Since acute vascular events involve the inner retina, they have a dramatic and distinct funduscopic appearance. When a retinal artery becomes occluded, the normally transparent retina supplied by that artery becomes white and edematous. There may be segmentation of the arteriolar blood column (boxcarring), a reduction of the arteriolar lumens, and sometimes visible emboli (Figure 1-18). These acute retinal infarctions should be evaluated urgently in a stroke unit similar to acute cerebral infarctions.

Figure 1-18.

Central retinal artery occlusion in the left eye. Multiple emboli are present in the retinal arteries, the ischemic retina is pale, and a cherry red spot can be seen at the macula.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Occlusion of the central retinal vein produces a dramatic funduscopic appearance in which the retinal veins are markedly dilated with diffuse hemorrhages involving the inner layers of the retina. Also usually present are cotton wool spots (small infarctions of the nerve fiber layer) and swelling of the optic nerve head. These retinal vascular disorders are discussed more fully later in this CONTINUUM issue in the article “Retinal and Optic Nerve Ischemia,” by these same authors.

A retinal detachment occurs when the connections between the overlying retina and the underlying retinal pigment epithelium (and the nourishing choroidal blood supply) are severed. If the detachment involves the retina centrally, poor central vision and a relative afferent pupillary defect result. Ophthalmoscopy will reveal the detached retina ballooning forward or simply a red reflex with an obscured view of the fundus. Myopic patients are especially vulnerable to retinal detachments, as are patients who have recently had intraocular surgery or ocular trauma or have a family history of retinal detachment. Detachments are often heralded by photopsias (flashes of light). If the detachment originates peripherally, patients may first experience a period of time when they notice a veil or shadow over a portion of the visual field prior to central visual involvement. Prompt evaluation by an ophthalmologist may preempt further detachment and allow for the appropriate reattachment surgery.

Once it has been determined by history and examination that a patient has an optic neuropathy, a differential diagnosis as to the underlying cause of that optic neuropathy must follow. Essentially all categories of disease processes must be considered (Table 1-3 and Table 1-4).

Table 1-3.

Categories of Disease Processes that Can Cause an Optic Neuropathy

Table 1-4.

Clinical Characteristics of Common Optic Neuropathies

The optic nerve has a very limited repertoire of how it can express itself when it is damaged or perturbed. If the pathology involves the optic nerve head, swelling of the nerve, so-called disc edema, may be seen (Figure 1-19). If the locus of the pathology is behind the eyeball, termed retrobulbar, it is likely that the optic nerve will appear normal at the time of acute visual loss (Figure 1-20). Ultimately, after 4 to 6 weeks, pallor will ensue if permanent damage has occurred (Figure 1-21). Important clues in establishing the etiology of an optic neuropathy include the age of the patient, the tempo of onset and progression of visual loss, the presence or absence of pain, the presence or absence of bilateral involvement, the level of visual acuity, the pattern of visual field loss, the appearance of the optic nerve head, and the presence or absence of associated signs. Classically unilateral optic neuropathies include those of inflammatory, ischemic, and compressive etiologies. Inflammatory optic neuropathies typically manifest as acute or subacute central visual loss associated with pain. Ischemic optic neuropathies have acute central or altitudinal vision loss, usually without pain. Compressive or infiltrative optic neuropathies are typically slowly progressive, although commonly the visual loss may be incidentally found when the uninvolved eye is covered (Case 1-4 and Case 1-5). Succeeding articles in this CONTINUUM issue are devoted to all the various causes of optic neuropathies.

Figure 1-19.

Left optic nerve edema. The margins are blurry and elevated, and a few peripapillary hemorrhages are present.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-20.

Normal left optic nerve. The disc margins are sharp and the rim is pink. The cup-disc ratio is approximately 0.3.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-21.

Right optic nerve pallor.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Case 1-4

A 15-year-old girl was referred for a neuro-ophthalmic evaluation prior to surgical resection of a pituitary adenoma. Her pituitary adenoma had been known for 2 years, at which time she presented with secondary amenorrhea and galactorrhea. Her prolactin level was elevated, and she was treated with bromocriptine. She underwent biannual follow-up with MRIs. She denied any visual loss and never had formal visual field testing.

On examination, her visual acuity was 20/20 in both eyes. She read eight of 14 color plates with both eyes. There was no relative afferent pupillary defect. Funduscopic examination showed mild temporal pallor in both eyes. Visual fields showed a bitemporal hemianopia (Figure 1-22). She subsequently underwent an uncomplicated transsphenoidal resection of her pituitary adenoma. Repeat visual fields 3 months later were improved.

Figure 1-22.

Bitemporal hemianopia on a Humphrey 24-2 visual field (the dark parts are not seen). The left eye is shown on the left and the right eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Comment. This patient developed a bitemporal homonymous hemianopic defect as the result of chronic chiasmal compression by a known pituitary tumor. She was considered visually asymptomatic but never had formal visual field testing. Automated perimetry is a sensitive way to detect visual field defects in patients with pituitary tumors and should be obtained systematically and be part of the routine follow-up.

Case 1-5

A 55-year-old woman presented with 6 months of painless visual loss in the left eye. She had been evaluated by an ophthalmologist 1 month prior to this presentation, at which time she had visual acuity of 20/40 in the left eye, a left relative afferent pupillary defect, an enlarged blind spot in the left eye, and a mildly pale left optic nerve. MRI of the brain showed nonspecific white matter changes, and a diagnosis of optic neuritis, possibly related to multiple sclerosis, was made. She was referred for a second opinion regarding her risk of developing clinical multiple sclerosis.

On examination, her visual acuity was 20/20 in the right eye and 20/50 in the left eye. Color vision was slightly decreased in the left eye, and she had a left relative afferent pupillary defect. Visual field testing showed an enlarged blind spot in the left eye, and funduscopic examination showed temporal pallor of the left optic disc. Review of her MRI revealed that it had been performed without contrast and without orbital images. Because her clinical history of slowly progressive, painless optic neuropathy did not suggest optic neuritis, but rather a compressive optic neuropathy, the MRI was repeated with orbital views with fat suppression and contrast. It showed enhancement of the left optic nerve sheath, suggesting an optic nerve sheath meningioma (Figure 1-23). Intracranial extension was absent. On follow-up examination 1 month later, her visual field defect was slightly worse. She was then offered to be treated by external radiation.

Figure 1-23.

Axial T1-weighted MRI with fat suppression and contrast showing enhancement of the left optic nerve sheath (green arrows) suggestive of a left optic nerve sheath meningioma compressing the optic nerve (yellow arrows).

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Comment. The patient’s presentation was not typical for optic neuritis in that she had no pain on eye movement and the visual loss was progressive without significant improvement over a period of 6 months. Appropriate neuroimaging should have been obtained initially. CT scan and MRI of the brain do not necessarily provide an appropriate view of the intraorbital portion of the optic nerve, and even orbital MRI, if not performed with special fat-suppression techniques and with contrast, may miss optic nerve pathology.

TRANSIENT BINOCULAR VISUAL LOSS

Transient binocular visual loss commonly appears in the visual prodrome, or aura, of migraine. Typically patients see a small scotoma in homonymous portions of the visual field, surrounded by jagged, luminous, shimmering edges. The scotoma enlarges over several minutes, then gradually disappears, characteristically followed by a hemicranial throbbing headache on the side opposite the involved hemifield. The visual loss may progress to a complete homonymous hemianopia (Case 1-6). Even observant patients may perceive the visual loss as strictly monocular on the side of the temporal hemianopia. Visual field testing at the time, however, will confirm the homonymous nature of the defect. Patients may experience the visual aura of migraine without an associated headache, a so-called acephalgic migraine.

Case 1-6

A 65-year-old woman had episodic visual loss. Her past medical history was notable for hypertension and chronic but stable angina. In her twenties and thirties, she had experienced episodic headaches with nausea, photophobia, and phonophobia, but with no associated visual phenomena. She had a family history of migraine. Two years before the present examination she had begun to experience episodes of bilateral visual disturbances, which she described as the appearance of a jagged silver or gold line just off the center of vision in both eyes. The line enlarged over approximately 5 to 10 minutes, enclosing a central area inwhich vision was too blurred to recognize faces. After 20 minutes, the process gradually broke up like a puzzle and normal vision was restored. She denied associated headache or eye pain. Such episodes occurred twice a month and were not increasing in frequency. She had experienced no other neurologic deficits. Examination was completely normal.

Comment. This woman presented with a typical history of migrainous visual aura without headache. The characteristic buildup of positive visual symptomatology over time, the duration of the episodes, their occurrence over years, the lack of other neurologic symptoms or signs, and the lack of any residual abnormality on examination all attested to the benign nature of these events. The absence of headaches is common after age 50.

In older patients, episodes of transient, complete binocular visual loss may represent a TIA in the distribution of the basilar artery or the posterior cerebral arteries. Cardiac disease and disease of the more proximal vertebral-basilar system must be considered as embolic sources. Less commonly, a TIA manifests as a transient homonymous hemianopia. Hemianopic events of ischemic origin are typically sudden in onset, unlike those of migraine. Associated headache may be present, especially over the brow contralateral to the visual field loss. The pain, however, is usually coincident with the visual loss. Conversely, migraine symptoms build up over minutes, are stereotypic in nature, and are accompanied by positive phenomena.

Less common causes of transient binocular visual loss include bilateral transient visual obscurations from underlying disc edema, focal occipital seizures, and head trauma, especially in children. Causes of cerebral blindness lasting hours or days include the posterior reversible encephalopathy syndrome (eg, from hypertensive encephalopathy, preeclampsia/eclampsia, or the toxicity of chemotherapeutic agents such as cyclosporine).

PERSISTENT BINOCULAR VISUAL LOSS

Persistent binocular visual loss results from damage to both eyes, both optic nerves, the chiasm, or the retrochiasmal visual pathways (Figure 1-1). If visual field testing reveals visual loss that respects the vertical meridian, the lesion must be at the level of the chiasm or more posterior. If visual acuity is affected because of a retrochiasmal lesion, visual acuity must be symmetric and the lesions must be bilateral, involving both retrochiasmal pathways. If visual acuity is asymmetric, at least some additional abnormality of the pathways of vision anterior to the chiasm (ie, the eyes or optic nerves) must be present.

When optic neuropathies are bilateral and symmetric, all criteria for diagnosis of optic neuropathy may be met except for the presence of a relative afferent pupillary defect. These primary bilateral optic neuropathies may be difficult to distinguish from a group of retinal disorders, commonly designated retinal degenerations or dystrophies, in which secondary optic disc pallor occurs bilaterally. The retinal disorders that classically may masquerade as bilateral optic neuropathies include retinal degenerations that preferentially involve the cones, vitamin A deficiency retinopathies, toxic retinopathies, and carcinoma-associated and melanoma-associated paraneoplastic retinopathies. Optic nerve pallor may be present, but some degree of retinal arterial attenuation usually also occurs. The cone dystrophies in particular are characterized by bilateral loss of central vision, profound color vision deficits, an inability to see well in bright light with associated photophobia, and frequently a relatively normal-appearing fundus examination except for bilateral disc pallor, until later in their course when macular changes appear (Figure 1-24). An electroretinogram is usually diagnostic in these disorders.

Figure 1-24.

Bilateral cone dystrophy. Both maculae have an abnormal appearance; the optic nerves are mildly pale and the retinal arteries are attenuated. The right eye is shown on the left and the left eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Certain optic neuropathies are more commonly bilateral. Bilateral optic neuropathies can result from compressive lesions near the chiasm, especially if the chiasm is relatively posterior to the pituitary fossa (a so-called postfixed chiasm). Visual acuity is usually decreased in at least one eye. If both optic nerves are equally involved, a relative afferent pupillary defect may be absent. When the process has occurred over a long period of time, optic disc pallor may be present. Nutritional deficiency or toxins can cause optic neuropathies and typically result in bilateral, symmetric, and progressive visual loss; the classic visual field defect is a cecocentral scotoma (ie, involving fixation and the region between fixation and the physiologic blind spot) (Figure 1-25). The hereditary optic neuropathies are also characterized by bilateral progressive visual loss, cecocentral scotomas, and ultimately optic atrophy; dominant optic atrophy with an insidious, symmetric, and slowly progressive course; and Leber hereditary optic neuropathy with a more subacute, and often sequential, severe visual impairment.

Figure 1-25.

Bilateral optic neuropathies from ethambutol toxicity. A, Goldmann visual fields showing a central scotoma in each eye. The left eye is shown on the left and the right eye is shown on the right. B, Bilateral mild temporal optic nerve pallor. The right eye is shown on the left and the left eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Primary open-angle glaucoma is the most common bilateral optic neuropathy in the Western world. Elevated intraocular pressures associate with enlarged cup-disc ratios (Figure 1-26) and visual field defects. Visual impairment is typically in the form of peripheral visual field loss with sparing of central visual acuity until late in the disease process, often causing patients to be unaware of any deficits until then. Patients with enlarged optic cups on funduscopic examination or a family history of glaucoma warrant regular ophthalmic screening for glaucoma.

Figure 1-26.

Bilateral large cup-disc ratio from chronic open-angle glaucoma. The right eye is shown on the left and the left eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Visual field defects of patients with chiasmal or retrochiasmal lesions may go unnoticed as long as central visual acuity is spared. However, they may be functionally compromised by their visual deficits without recognizing them as such, with resultant motor vehicle accidents or other injuries. They may have associated neurologic symptoms, such as lateralizing numbness or weakness, difficulties with speech or language, diplopia, endocrine symptoms, or headache, some of which may suggest the location of the causative lesion. Bitemporal visual field defects that respect the vertical meridian are diagnostic of lesions, almost always compressive in etiology, at the optic chiasm. Associated symptoms and signs may reflect involvement of the adjacent cavernous sinus (eg, diplopia, ptosis, anisocoria, facial numbness or pain), hypothalamic-pituitary axis (eg, changes in behavior, polyuria, galactorrhea, amenorrhea, heat or cold intolerance, decreased libido, impotence, acromegaly), or ventricular obstruction (eg, headache, somnolence, incontinence, gait disturbance, vertical gaze abnormalities, pupillary light-near dissociation, papilledema). The most common causes of chiasmal syndromes are pituitary adenomas, meningiomas, craniopharyngiomas, and aneurysms. Imaging, preferably MRI, is mandatory for patients presenting with bitemporal hemianopia (Figure 1-27).

Figure 1-27.

Sagittal T1-weighted MRI of the brain showing a large pituitary tumor compressing the chiasm.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

A homonymous hemianopia results from injury to the contralateral optic tract, lateral geniculate body, visual radiations, or occipital cortex. Visual acuity in the intact homonymous hemifield in each eye should be normal. A complete homonymous hemianopia has no further localizing value (Figure 1-28). However, an exquisitely congruous partial homonymous defect most often localizes to the occipital lobe (Figure 1-29). The occipital lobe is the most common location for lesions causing isolated homonymous hemianopia, and the most common cause of occipital lobe damage is vascular disease (Figure 1-30) (Case 1-7). Associated symptoms and signs may help to localize the lesion along the visual pathways (Figure 1-1).

Figure 1-28.

Complete left homonymous hemianopia on a Humphrey 24-2 visual field (the dark parts are not seen). The left eye is shown on the left and the right eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-29.

Incomplete, congruous right inferior homonymous hemianopia on a Humphrey 24-2 visual field (the dark parts are not seen). The left eye is shown on the left and the right eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-30.

Fluid-attenuated inversion recovery (FLAIR) T2-weighted axial MRI of the brain showing a small left occipital infarction.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Case 1-7

An 82-year-old man reported acute binocular visual loss. His past medical history was notable for coronary artery disease with previous myocardial infarction and heavy cigarette use. No other neurologic symptoms were present. Family history was notable for coronary artery disease and strokes.

On examination, visual acuity was 20/100 in both eyes and color vision was impaired in both eyes. Pupils, motility, and fundi were normal. Visual field testing demonstrated bilateral congruous homonymous hemianopias (Figure 1-31). The remainder of the neurologic examination was normal. MRI of the brain showed evidence of bilateral occipital infarctions (Figure 1-32), and an echocardiogram demonstrated an apical clot in the left ventricle. The patient was placed on warfarin. Visual fields and neurologic status persisted unchanged.

Figure 1-31.

Goldmann visual fields showing bilateral homonymous hemianopias. A right homonymous superior quadrantanopia and a left homonymous inferior quadrantanopia are present. The left eye is shown on the left and the right eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Figure 1-32.

Axial T2-weighted MRI of the brain showing bilateral occipital infarctions.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

Comment. The shape of this patient’s visual field deficit and its isolated nature localized the lesion to the occipital lobes and suggested that the etiology was vascular. He had several risk factors for cerebral infarction, including atherosclerotic heart disease, cigarette use, and previous myocardial infarction. Echocardiography ruled out a valvular lesion but demonstrated a clot in the ventricle as the likely source of emboli.

The visual field defects resulting from occipital lobe injury are typically exquisitely congruous. Macular sparing occurs only with occipital lobe lesions, such as infarctions, that spare the most posterior aspect of the occipital cortex where macular representation resides, thus reflecting the anatomy of the striate cortex and its occasional dual blood supply from the posterior and middle cerebral arteries (Figure 1-33). Conversely, homonymous hemianopic scotomas are caused by selective involvement of the most posterior occipital pole. Most anterior in the striate cortex is the most peripheral representation of the visual field, the monocular temporal crescent. It is only with occipital lobe lesions that this crescent of peripheral visual field may be spared or selectively involved. Congruous homonymous quadrantic defects that strictly respect the vertical and horizontal meridians may reflect involvement of the superior or inferior parastriate cortices. The occipital lobe is the most common location for lesions causing an isolated homonymous hemianopia. Such lesions are predominantly vascular, eg, embolic occlusion of the posterior cerebral artery. Under these circumstances, the abrupt onset of homonymous hemianopia is often accompanied by pain over the brow ipsilateral to the stroke and contralateral to the field defect. Embolic occlusion of the posterior cerebral artery is the most likely cause. Alternatively, prolonged hypotension may result in watershed infarctions at the parieto-occipital junctions.

Figure 1-33.

Incomplete, congruous right homonymous hemianopia with macular sparing shown on a Humphrey 24-2 visual field (the dark parts are not seen). The left eye is shown on the left and the right eye is shown on the right.

Reprinted with permission from Biousse V, Newman NJ, Thieme.1 © 2009 Thieme Medical Publishers, Inc.

KEY POINTS

• The most important historical features are whether the visual loss is monocular or binocular, and whether it is transient or persistent.

• When examining a patient with visual loss, each eye must be tested separately.

• A consistent difference in color perception across the horizontal or vertical meridian may be the only sign of an altitudinal or hemianopic defect, respectively.

• When a relative afferent pupillary defect is demonstrated, the cause is almost always unilateral or asymmetric optic nerve dysfunction.

• In order to view the fundus to the best advantage, the pupils should be dilated.

• Loss of central visual function usually results from pathology in the optic nerve or the most central retina (the macula).

• In papilledema, the patient sees something (acuity unaffected) and the physician sees something (sign). In papillitis, the patient sees nothing (impaired acuity) but the physician sees something (sign). In optic neuritis, the patient sees nothing (impaired acuity) and the physician sees nothing (normal examination).

• Transient visual obscurations are characterized by brief blackouts of vision and are usually a symptom of underlying papilledema.

• The term papilledema is reserved for disc edema secondary to elevated intracranial pressure.

• In contrast to the persistent visual loss encountered in most other causes of disc edema, visual acuity is typically normal in patients with papilledema.

• Painful transient monocular visual loss should suggest giant cell arteritis, ocular ischemic syndrome, carotid artery dissection, or angle-closure glaucoma.

• Optic disc pallor, reflecting atrophy of the optic nerve fibers, does not appear until at least 4 to 6 weeks after injury.

• It is usually impossible to differentiate among the various causes of optic disc edema or pallor by the appearance of the disc alone.

• The most common cause of transient binocular visual loss is the visual aura that occurs with migraine.

• Bitemporal visual field defects that respect the vertical meridian are diagnostic of lesions at the optic chiasm, and these are almost always compressive in etiology.

• For a retrochiasmal process to cause loss of visual acuity, the lesions must be bilateral.

• Reduced visual acuity from a retrochiasmal lesion is always identical in both eyes.

• The occipital lobe is the most common location for lesions causing isolated homonymous hemianopia, and the most common cause of occipital lobe damage is vascular disease.