Homonymous hemianopia

INTRODUCTION — Homonymous hemianopia is a visual field defect involving either the two right or the two left halves of the visual fields of both eyes. It is caused by lesions of the retrochiasmal visual pathways, ie, lesions of the optic tract, the lateral geniculate nucleus, the optic radiations, and the cerebral visual (occipital) cortex (figure 1) [1-4]. Characteristics of the visual field abnormalities (type, form, size, and congruity), along with associated neurologic signs and symptoms, have been traditionally used for localizing pathologic lesions in the brain (table 1) [1-6].

Homonymous hemianopia is often disabling, causing difficulties with reading and visual scanning. Patients may fail to notice relevant objects or avoid obstacles on the affected side, causing collisions with approaching people or cars. They are not legally allowed to drive in most states. This has dramatic consequences on their vocational and private lives [1,7].

This topic will discuss homonymous hemianopia as a fixed deficit; it may be a transient phenomenon resulting from migraine, transient cerebral ischemia, or seizure. This is discussed separately. (See "Amaurosis fugax (transient monocular or binocular visual loss)", section on 'Causes of transient binocular visual loss'.)

ETIOLOGY — Any type of intracranial lesion in the appropriate location can cause a homonymous hemianopia; however, vascular causes (cerebral infarction and intracranial hemorrhage) are the most frequent in adults, ranging from 42 to 89 percent, followed by brain tumors, trauma, surgical interventions, and other central nervous system diseases [1,8-13]. In children, neoplasms are the most common cause of homonymous hemianopia (39 percent), followed by cerebrovascular disease (25 percent) and trauma (19 percent) [14]. Homonymous hemianopia after head trauma may be underrecognized; multifocal brain injury is more common in this setting, contributing to other neurologic deficits that may overshadow the visual field defect [13].

Uncommon causes of homonymous hemianopia include multiple sclerosis, infections (encephalitis, abscess), degenerative dementia (posterior cortical atrophy), Creutzfeldt-Jakob disease, adrenoleukodystrophy, seizures, and severe hyperglycemia [12,15-21]. (See "Clinical features and diagnosis of Alzheimer disease", section on 'Atypical presentations'.)

NEUROANATOMY OF THE VISUAL PATHWAYS — There is a retinotopic arrangement of the nerve fibers in the visual pathways, which is responsible for the specific patterns of visual field defects. A homonymous hemianopia points to unilateral lesions of the visual sensory pathways posterior to the optic chiasm (figure 1).

Optic chiasm and tracts — At the optic chiasm, the nerve fibers from the temporal retina (nasal visual field) maintain their relative position in the lateral chiasm before passing into the ipsilateral optic tract, while the nerve fibers from the nasal retina (temporal visual field) decussate in the chiasm and pass into the contralateral optic tract.

Each optic tract contains crossed and uncrossed nerve fibers subserving the contralateral visual field; the fibers in the left optic tract contain fibers carrying information for the right half of the visual field from both the right and left eyes. Lesions of the optic tract affect the temporal fibers and nasal visual field of the ipsilateral eye and the nasal fibers and temporal visual field of the contralateral eye, giving rise to homonymous visual field defect of the contralateral visual field (figure 1). The optic tract lies in close proximity to the internal capsule, cerebral peduncle, and basal ganglia.

The separation of the two hemifields occurs at the vertical raphe of the retina (through the fovea centralis retinae), implying that the visual field is split at the point of fixation into the right and the left halves. Thus, macular fibers are also both crossed and uncrossed in the optic chiasm.

Lateral geniculate nucleus — Most (80 percent) of the nerve fibers in the optic tract project into the ipsilateral lateral geniculate nucleus in the thalamus. Other optic tract fibers innervate the Edinger-Westphal nuclei in the pretectum, providing the afferent limb for the pupillary light reflex. The axons from the ipsilateral eye terminate in the second, third, and fifth laminae of the lateral geniculate nucleus, while the axons from the contralateral eye terminate in the first, fourth, and sixth laminae. The nerve fibers are believed to form a precise retinotopic map in the lateral geniculate nucleus.

Optic radiations — The neurons originating from the lateral geniculate nucleus form the optic radiations or the geniculocalcarine tract and end in the primary visual cortex in the occipital lobe.

The superior fibers of the optic radiations subserve the inferior visual field and pass posteriorly through the parietal lobe. The inferior fibers, which subserve the superior visual field, initially course anteriorly, superior to, and around the temporal horn of the lateral ventricle. They then pass laterally and posteriorly to the striate cortex, forming Meyer's loop (figure 1). It is believed that as these fibers approach the occipital cortex, their retinotopic order increases, and the left and right eye fibers representing common visual loci fall into closer register and ultimately into ocular dominance columns in the striate cortex [16].

Visual cortex — The primary visual cortex (also called the calcarine cortex, striate cortex, Brodmann area 17) is believed to be retinotopically organized based on visual information from the corresponding retinal loci from the two eyes. The upper lip of the calcarine cortex receives projections from the inferior visual field, while the lower lip of the calcarine cortex receives information from the superior visual field. The posterior pole of the occipital lobe is concerned with the central visual field, while the peripheral visual field is represented in the most anterior part of the striate cortex.

The striate cortex is surrounded by the visual association areas (Brodmann areas 18 and 19). These areas are also believed to be retinotopically arranged with significant representation for the central visual field, as in the primary visual cortex [1-4].

COMMON VISUAL FIELD DEFECTS — The visual cortex receives a point-to-point projection that corresponds to the retinal image of the visual fields. The fields are divided into temporal and nasal halves that respect the vertical meridian; the temporal field is somewhat larger than the nasal field. The point of visual fixation is represented centrally. The blind spot represents the optic disc and is located 15 degrees temporal to fixation.

Terminology — A homonymous hemianopia is complete when the visual field defect respects the vertical meridian, has macular splitting, and involves the entire hemifield on the affected side (figure 2). All other visual field defects are defined as partial or incomplete (table 1).

Incomplete homonymous hemianopias are defined as congruous if the homonymous defects in fields of the two eyes are identical in shape, depth, and size (figure 3). Other incomplete homonymous hemianopias are called incongruous (figure 4). It is important to emphasize that the concept of congruency applies only to incomplete homonymous hemianopias. Because of the anatomic organization of the visual pathways, congruous homonymous hemianopias are usually related to lesions involving the most posterior part of the visual pathways (ie, the occipital lobe). Lesions of the anterior radiations and optic tract are usually incongruous (figure 1 and figure 4).

Congruency is a helpful but not always reliable feature for localizing lesions to the anterior versus posterior portions of the visual pathways. In one case series, congruency of incomplete hemianopias was seen in 83 percent of lesions attributed to occipital lobe lesions and 50 percent of those with optic tract pathology [22].

Incomplete homonymous hemianopias include homonymous quadrantanopia, homonymous hemianopia with macular sparing, homonymous scotomatous defect, homonymous sectoranopia, unilateral loss of temporal crescent, and temporal crescent-sparing homonymous hemianopia.

Complete homonymous hemianopia — A complete left or right visual field defect can occur with complete lesions anywhere along the retrochiasmal visual pathway (figure 2). In one study of 852 patients with homonymous hemianopia, 38 percent were complete [12].

Homonymous quadrantanopia — Superior and inferior homonymous visual field defects respecting the vertical and sometimes the horizontal meridians (figure 5) were the most common incomplete homonymous hemianopias in one large case series [12]. These defects occur when lesions (especially infarcts) selectively damage either the inferior or superior banks of the occipital cortex (image 1). Less commonly, a quadrantanopia represents a lesion in the optic radiations in the temporal or parietal lobe [23].

Homonymous hemianopia with macular sparing — Homonymous visual field defects sparing the central 5 to 25 degrees of visual field on the affected side (figure 6) are common when the posterior half of the occipital region has been at least partially spared by the lesion. Because of the dual vascular supply of the occipital pole in many individuals (by branches of both the middle and posterior cerebral arteries), macular-sparing homonymous hemianopia is more likely to occur with stroke than with other occipital lesions. While classically associated with occipital lobe injury, macular sparing may also represent incomplete damage to the optic radiations and, less commonly, to the optic tracts [12].

It is important to emphasize that macular sparing of 3 degrees or less is not clinically meaningful, as it may be the result of wandering fixation. Also, macular sparing should be diagnosed only when there is good fixation on visual field testing [12].

Homonymous scotomatous defect — Homonymous visual field defects respecting the vertical meridian and limited to the central 30 degrees are usually enclosed within an area of normal peripheral visual field (figure 7). These defects are the converse of macular-sparing homonymous hemianopia. The cause is most commonly occipital tip injury, most frequently due to stroke or trauma (image 2). However, larger lesions involving the occipital cortex and lesions in the occipital radiations and optic tract have also been associated with this defect [12,24].

Homonymous sectoranopia — Wedge-shaped defects located near the horizontal meridian, either pointed at fixation or sparing fixation (figure 8), are characteristic of lesions involving the lateral geniculate body (usually infarctions). These are relatively unusual visual field defects. The visual field patterns are based on the lateral geniculate body's dual blood supply from the anterior and posterior choroidal arteries.

Unilateral loss of temporal crescent — The most peripheral 30 degrees of the temporal field viewed by each eye is not overlapped by a corresponding nasal field in the other eye. This portion of the field is called the temporal crescent and has monocular representation in the anterior part of the contralateral visual cortex.

These rare visual field defects are secondary to lesions involving the anterior 10 percent of the primary visual cortex (figure 9). The lesion is usually an infarction [25]. Unilateral loss of temporal crescent is the only example of a monocular visual field defect caused by a retrochiasmal lesion (all other defects are bilateral and homonymous).

Temporal crescent-sparing homonymous hemianopia — When the anterior portion of the primary visual cortex is spared by an occipital lesion producing a homonymous hemianopia, there is sparing of the temporal crescent on the contralateral eye visual field (figure 10). A small percentage (<20 percent) of individuals with this pattern of vision loss will have lesions of the optic radiations instead [26]. The temporal crescent is particularly sensitive to moving stimuli, making this lesion somewhat less disabling.

The unilateral loss of, or preservation of, the temporal crescent is more likely to be detected with Goldmann perimetry rather than automated perimetry (eg, Humphrey visual fields or the Octopus), which concentrates on the central 30 percent of the visual field.

CLINICAL FEATURES — Patients with homonymous hemianopia may not complain specifically of visual field loss. They may complain instead of monocular vision loss or of an ill-described difficulty with seeing or reading (dyslexia). Unilateral retrochiasmal lesions producing homonymous hemianopia do not affect visual acuity. Complaints of visual impairments, therefore, should prompt an examination of the visual fields as well as of visual acuity. (See "The detailed neurologic examination in adults", section on 'Visual fields'.)

Characteristics of the visual field defect as described above, along with accompanying neurologic signs, help to localize the lesion within the brain; occipital lobe lesions are most common [12].

Lesions of the optic tract — Lesions of the optic tract account for 3 to 11 percent of all homonymous hemianopias. Optic tract lesions produce characteristic clinical features, which are exquisitely localizing (figure 1) [1,27,28].

●Lesions of the optic tract produce either complete or incomplete homonymous hemianopia. When incomplete, the visual field defect is often (but not always) incongruous [22]. Rarely, small lesions of the optic tract may produce congruent homonymous scotomatous defects [29].

●Isolated lesions of the optic tract produce a relative afferent pupillary defect in the eye contralateral to the side of the lesion (eye with the temporal field loss). Another pupillary phenomenon commonly ascribed to lesions of the optic tract is pupillary hemiakinesia (hemianopic pupillary reaction or Wernicke pupil). When a sharp focused beam of light is projected onto the retina from the intact hemifield, the pupil is found to constrict normally. However, when light is shone from the blind hemifield, the pupillary reaction is either decreased or absent [1]. In practice, it may be difficult to demonstrate the hemianopic pupillary reaction; light often scatters across the iris, stimulating the intact field and producing pupillary constriction.

●Lesions of the optic tract cause a characteristic pattern of optic atrophy. While the eye ipsilateral to the side of injury develops diffuse pallor, the contralateral optic disc develops a horizontal band of pallor in a "bow-tie" configuration within four to six weeks after the injury (figure 11 and picture 1).

●Patients with optic tract lesions may also show neurologic deficits related to hypothalamic signs and symptoms and contralateral hemiparesis from contiguous internal capsular damage.

Lesions of the lateral geniculate nucleus

●Visual field defects resulting from lesions of the lateral geniculate nucleus are of variable nature because of the intricate retinotopic organization of the lateral geniculate nucleus. The nature of the visual field defect is also influenced by the underlying cause. Vascular lesions of the lateral geniculate nucleus usually produce congruous and characteristic visual field defects [1-4,30,31]. Occlusion of the posterior choroidal artery causes a wedge defect that straddles the horizontal meridian region (sectoranopia), while occlusion of the anterior choroidal artery spares that sector of visual field (sector-sparing) (figure 8) [1-4,30,31].

●The pupillary reactions in patients with lesions of the lateral geniculate nucleus are normal, unless there is involvement of the optic tract or the brachium of the superior colliculus, which produces a contralateral relative afferent papillary defect.

●Patients with lesions of the lateral geniculate nucleus may also show signs and symptoms suggestive of damage to the ipsilateral thalamus (contralateral hemihypoesthesia, abnormal referred pain on the contralateral side) and/or pyramidal tract (contralateral motor weakness).

Lesions of the optic radiations — The optic radiations project from the lateral geniculate nucleus to the striate cortex (figure 1).

●The first part of the optic radiations makes up the most posterior limb of the internal capsule. Here, the optic radiations lie in close proximity to the corticospinal and corticobulbar tracts, as well as the thalamocortical fibers. Lesions of the optic radiation in this location typically produce a contralateral, usually complete, homonymous hemianopia, associated with contralateral hemianesthesia and hemiplegia. A relative afferent pupillary defect may also be observed in lesions that are proximate to the lateral geniculate body [32].

●Involvement of the optic radiations in the temporal lobe produce a homonymous defect, which is usually incomplete, incongruous, either confined to the superior quadrants or more dense superiorly than inferiorly, and often called "pie-in-the sky" defect [1-4]. Temporal lobe lesions also produce other neurologic manifestations, including aphasia, memory deficits (dominant hemisphere lesions), complex seizures, and auditory and visual hallucinations. Evaluations of visual field defects after temporal lobectomy in patients with epilepsy demonstrate 15 percent greater loss in the nasal than the temporal field and considerable interindividual variance, especially as regards the anterior extent of Meyer's loop [33,34].

●Involvement of the optic radiations in the parietal lobe usually produce incomplete, mildly incongruous homonymous hemianopia, which is either limited to the inferior visual fields or is more dense inferiorly than superiorly. However, large lesions may produce a complete homonymous hemianopia. Contralateral hemifield neglect is also seen in lesions of the nondominant hemisphere and can be difficult to distinguish from a visual field defect. Since the parietal lobe is the principal sensory area of the cerebral cortex, lesions often produce sensory deficits [1-4]. Lesions extending to the dominant angular gyrus lobe may also produce Gerstmann syndrome (finger agnosia, agraphia, acalculia, and right-left disorientation), while lesions of the nondominant parietal lobe may cause inattention or neglect and impaired constructional ability [1-4].

Lesions of the occipital lobe — Occipital lobe lesions are the most common cause of homonymous hemianopia and are most often vascular in origin [8-10]. Lesions of the occipital lobe tend to produce an isolated homonymous hemianopia (ie, not associated with other neurologic deficits). Depending on the location of the lesion, various visual field patterns are seen.

●Lesions of the occipital pole (most posterior aspect of the striate cortex) typically cause congruous homonymous scotomas (figure 1 and figure 7) [35]. Lesions extending to the dominant angular gyrus lobe may also produce Gerstmann syndrome [1-4].

●Lesions of the most anterior part of the striate cortex produce homonymous defects involving the peripheral visual field (temporal crescent) (figure 9). Conversely, large lesions of the posterior occipital lobe may produce a homonymous hemianopia with sparing of the contralateral crescentic temporal visual field (figure 10). Unilateral temporal crescent may be missed if only the central visual field is tested, as is common with automated perimetry. In cases with unilateral temporal visual field defects, the nasal retinal periphery should be carefully examined, as lesions in this location may also produce unilateral temporal visual field defects [1-4].

●Homonymous hemianopia due to occipital lesions often has macular sparing (sparing of the central visual field) (figure 6). Explanations for this phenomenon include bilateral representation of the macula in the occipital cortex, incomplete damage to the striate cortex on the affected side, and, more commonly, dual blood supply of the occipital pole by middle and posterior cerebral arteries [1-4].

●A right homonymous hemianopia may be accompanied by alexia if the lesion involving the left occipital lobe extends anteriorly to involve the splenium of the corpus callosum [36]. Because patients often retain the ability to write (if the angular gyrus is spared), this classic syndrome is generally referred to as "alexia without agraphia."

●Bilateral homonymous hemianopias are produced by bilateral lesions of the occipital lobe, either simultaneously or consecutively. The extent of the visual field defect depends on the extent of involvement of the striate cortex and can include a combination of visual field defects such as bilateral complete hemianopias (cortical blindness), "checkerboard" field defects, and combinations of complete homonymous hemianopia, scotomatous, and altitudinal defects (figure 12 and figure 13). In cases with bilateral homonymous hemianopia, visual acuity may be reduced. It is important to emphasize that the amount of visual loss should be symmetric in both eyes, unless patients have another anterior visual pathway cause for their decreased visual acuity. Cortical blindness may be accompanied by a striking anosognosia, in which patients are unaware of their deficit; this is called Anton's syndrome.

●A lesion involving the extrastriate cortex produces congruous quadrantic visual field defects (figure 5).

EVALUATION AND DIAGNOSIS

●Confrontation testing – Confrontation testing of the visual fields is commonly performed at bedside to screen for visual field defects. Techniques are described separately. Comparison of these techniques found that they had poor sensitivity (35 to 74 percent) for the detection of visual field abnormalities [37,38]. Use of a small, red target gave the most sensitive results. Combining two confrontation tests can improve sensitivity.

●Visual field perimetry – In addition to increased sensitivity, formal visual field perimetry gives more information regarding the type, size, and form of the visual field loss. These tests include automated static perimetry as well as manual kinetic perimetry (eg, Goldmann perimetry). These are similarly reliable in their ability to detect the presence of a homonymous hemianopia. However, the manual kinetic techniques are easier to perform for patients with neurologic deficits and, in one study, were more predictive of the lesion location on magnetic resonance imaging (MRI) [39].

Perimetry should be performed in all patients with neurologic lesions that may produce a visual field defect. Confrontation perimetry at bedside is insufficient to identify and follow visual field changes. Formal visual fields are important from a medicolegal point and are also useful prior to allowing a stroke patient to drive or return to work. (See 'Driving' below.)

●Evaluation for underlying etiology – All patients with homonymous hemianopia require neuroimaging, usually MRI study, to define the underlying etiology. (See 'Etiology' above.)

In cases in which there is no underlying MRI abnormality, neurodegenerative disease is often the underlying cause [15].

PROGNOSIS — The rate of spontaneous improvement of homonymous hemianopia varies greatly, between 18 to 67 percent, and depends to a large extent on the time period after the brain injury when the visual fields were tested [1-4,9,13,40-42]. One study reported 46 percent spontaneous improvement of homonymous hemianopia within three weeks from onset of ischemic stroke event [42]. Another study reported 67 percent spontaneous recovery of homonymous hemianopia (by confrontation method) within one month of a stroke [41]. Spontaneous improvement of the visual field defect is unlikely after six months from the injury unless there is an improvement of the underlying disease, such as can occur in multiple sclerosis [1,13,43].

While it seems likely that lesion size and location and underlying cause play an important role in the recovery of visual field deficits, the evidence is somewhat conflicting. In one study of 113 patients with homonymous hemianopia from a variety of causes, no patient, lesion, or visual field characteristic was found to correlate with the final visual outcome [43]. By contrast, in a study in a more restricted population of 31 individuals after occipital lobe stroke, a better recovery of visual fields was noted in patients with a smaller lesion size and in whom the striate cortex was spared [35].

DRIVING — Most patients with homonymous hemianopia secondary to a stroke are unaware of their visual field defect and may continue to drive, if not otherwise disabled from doing so [44]. Patients should be aware that driving abilities are compromised by a homonymous hemianopia [45]. In most states of the United States, patients with a complete homonymous hemianopia are not legally allowed to drive.

Medically, it is intuitive that if a person misses large parts of their visual field, especially an entire half, then they would not be safe on the road. Decisions regarding the legality to drive are solely based on prescribed visual criteria, which differ for each state in the United States. It is the responsibility of the treating physician to counsel the patient regarding driving once it is determined that the patient no longer meets the minimum required vision criteria. However, it is not incumbent upon the treating physician to notify the Department of Motor Vehicles.

The American Academy of Ophthalmology summarizes the vision criteria for driving licenses in different states in the United States.

TREATMENT AND REHABILITATION — In most patients with homonymous hemianopia, no or few treatments are usually offered. Some rehabilitation techniques have been suggested over the past decade but remain controversial. Although there is limited evidence supporting their efficacy, rehabilitation often improves patients' ability to adapt to their visual field defect by increasing attention and treating neglect when present [46-49]. The techniques are based upon three principles:

●Compensation (use of intact function)

●Substitution (adapt the patient's environment to the patient's functional impairment)

●Restitution (retraining the impaired function; ie, expanding the visual field)

One approach includes the use of hemianopic mirrors or prisms. The principle is to project the images from the blind hemifield onto the intact hemifield. However, these techniques may cause significant spatial disorientation and confusion for some patients [7,46,50]. While they may help with ambulation, they cannot be used for driving [51].

Patients with homonymous hemianopia experience considerable difficulty reading, especially when the visual field defect is complete or involves fixation. Patients with right-sided defects cannot see the letters immediately following the ones that they have read, while patients with left-sided defects have problems returning to the next line, as it falls in the blind hemifield [52,53]. These patients notice benefit in reading if they use their finger or a ruler positioned under each line of text, so that they do not lose the position while reading the text, or if they train themselves to read vertically. Computerized saccadic training programs may improve patients' visual function by training patients with homonymous hemianopia to make saccades into their blind hemifield [54-56]. Systematic reviews have reported that small studies suggest modest benefits in increased reading times and decreased reading and scanning errors using this approach [46,57].

Restorative methods are based upon the stimulation of a transition zone adjacent to the blind hemifield, resulting in visual field expansion, presumably due to cortical plasticity [50,58]. Although this concept remains debated with few studies demonstrating benefit [46,59,60], visual restoration therapy has been approved by the US Food and Drug Administration (FDA) and is used at some centers in the United States and in Europe [58]. It is considered helpful by some patients, most likely because of improved attention at the edge of the blind field rather than true expansion of the field; such methods also likely train patients to make small saccades into their blind hemifield.

Another investigational approach uses repetitive transcranial magnetic stimulation (rTMS) applied over the posterior parietal cortex [61]. The duration and clinical significance of the observed benefit needs to be defined in further study.

SUMMARY

●Definition and anatomy – Homonymous hemianopia represents a visual field defect relating to loss of vision in all or part of the left or right visual field in both eyes.

Homonymous hemianopia occurs with lesions in the retrochiasmal visual pathways: the optic tracts, the lateral geniculate body, the optic radiations, and the occipital cortex. (See 'Neuroanatomy of the visual pathways' above.)

●Etiology – Stroke is the most common etiology in one-half to two-thirds of patients, followed by traumatic brain injury, brain tumors, and other structural brain lesions. (See 'Etiology' above.)

●Clinical features and localization – Specific features of the visual field defect (type, form, congruity, and size), along with other neurologic symptoms and signs, help to localize the underlying lesion. These are summarized in the table (table 1). (See 'Common visual field defects' above and 'Clinical features' above.)

●Functional implications – While homonymous hemianopia may frequently go unrecognized by patients and clinicians, it is nonetheless disabling, impairing visual scanning and reading, and restricting driving. (See 'Treatment and rehabilitation' above.)

●Prognosis – Many patients will recover spontaneously from a stroke-related visual field defect; over half will do so within the first month. Recovery after six months is unlikely. (See 'Prognosis' above.)

●Rehabilitation – Treatment options are limited and include rehabilitation techniques aimed primarily at compensation and accommodation. (See 'Treatment and rehabilitation' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Xiaojun Zhang, MD, PhD, who contributed to earlier versions of this topic review.