Hemianopsia

Etiology

Homonymous Hemianopsia

Homonymous hemianopsia refers to a visual field defect that affects either the right or left halves of the visual fields in both eyes. Complete homonymous hemianopsia affects the entire hemifield of both eyes. Such a condition arises with a lesion anywhere along the retrochiasmal visual pathway. The remaining lesions are categorized as incomplete.

Incomplete homonymous hemianopias are further divided into 2 types—congruous and incongruous. Congruous homonymous hemianopia occurs when the homonymous defects in the fields of the 2 eyes are identical in shape, depth, and size. The remaining cases are categorized as incongruous.

Homonymous hemianopsia can result from various causes, including stroke, intracranial hemorrhage, head trauma, mass-occupying lesions, invasive surgical procedures, and neurological conditions such as multiple sclerosis, Alzheimer disease, and epilepsy.[3][4]   

Homonymous hemianopsia is an uncommon symptom caused by severe hyperglycemia.[5] A case presentation reveals homonymous hemianopia in a patient with diabetic ketoacidosis, supported by clinical, laboratory, and radiological findings. However, in such cases, the neurological symptom is transient, with reversible structural changes observed on magnetic resonance imaging (MRI).[6] In addition, seizures may present with hemianopsia in cases such as refractory status epilepticus due to stroke-like migraine attacks after radiation therapy (SMART).[7][8]

Homonymous visual field defects sparing the central 5° to 25° of the visual field on the affected side are frequently observed when the lesion has partially spared the posterior half of the occipital region. Due to the vascular supply of the occipital pole, which often involves branches from both the middle and posterior cerebral arteries, macular-sparing homonymous hemianopia is more prone to occur in strokes compared to other occipital lesions. 

Bitemporal Hemianopsia

Bitemporal hemianopsia is an ocular defect characterized by reduced peripheral vision in the outer temporal halves of the visual field in each eye. Typically, this condition arises from a tumor or lesion affecting the optic chiasm—the point of decussation for the optic nerve—responsible for visual information from the nasal retina in each eye.[9] 

Bitemporal hemianopsia is often associated with mass-occupying lesions such as pituitary adenomas, craniopharyngiomas, and meningiomas.[10] Basilar skull trauma, frontal bone fracture, or vascular lesions, such as anterior communicating artery aneurysms, have also been identified as causes of bitemporal hemianopsia.[11][12][13]

In a case report, a patient is identified with bilateral superior altitudinal hemianopsia (BSAH), where the primary etiology is a pituitary microadenoma leading to inferior optic chiasm damage. The visual field defect observed in the patient includes the macula. Despite the presence of multiple risk factors, including persistent migraine, hypothyroidism, or the potential for ischemic disease affecting the ocular and occipital vessels, imaging did not reveal any evidence of tissue ischemia or infarction that could explain the patient's visual field defects.[14] 

Rare reports of hemianopia exist as a possible adverse effect of vector-based vaccines such as COVID-19.[15] In addition, individuals with a previous history of shaken baby syndrome, when presenting with homonymous hemianopia, exhibit signs of slightly impaired higher visual function, and MRI scans reveal focal damage to the dorsal and ventral reading pathways.[16] 

Binasal Hemianopsia

Binasal hemianopsia is a rare condition that typically occurs in an incomplete form. Potential causes include bilateral internal carotid artery aneurysms, hydrocephalus, intracranial mass lesions, neurosyphilis, and elevated intracranial pressure. 

Epidemiology

The occurrence of hemianopsia varies depending on the underlying pathological condition. In adults, stroke stands out as the predominant cause, accounting for 69.7% of cases, with an average patient age of 58.[3][17] Conversely, in children, neoplasms contribute to 39% of cases, cerebrovascular disease to 25%, and trauma to 19%.[18] An extensive review involving 904 patients with homonymous hemianopsia highlights that stroke primarily affects the occipital lobe in 54% of patients, followed by involvement of the optic radiations in 33% and optic tracts in 6% of patients.

In non-stroke-related homonymous hemianopsia, damage can occur at various locations along the visual pathway. Specifically, 24% affect the occipital lobe, 31% impact the optic radiations, 19% involve the optic tract, and 25% affect multiple locations.[3][19] Pituitary adenomas are the most frequently encountered cause of bitemporal hemianopsia. A systematic review based on radiographic and autopsy studies estimates the overall prevalence of pituitary tumors to be 16.7%.[20] Conversely, occlusive cerebrovascular disease or occipital infarction is identified as the most common cause of homonymous hemianopia with macular sparing.[21]

History and Physical

Patients affected by a visual field defect may not explicitly express their concerns. Instead, they might describe monocular vision loss or a more general sense of visual challenges, such as dimmed vision or difficulty reading. Individuals with visual complaints should undergo a comprehensive physical examination, including a detailed neurological assessment. In cases where neurological emergencies are suspected, characterized by sudden alterations in mental status or the onset of new focal neurological deficits, it becomes crucial to promptly attend to vital signs and initiate immediate management of airway, circulation, and breathing.

A visual acuity test and a comprehensive cranial nerve assessment should be conducted in all individuals to evaluate for visual deficits. The examiner should pay specific attention to pupillary examination and visual field testing. A bitemporal visual field defect helps localize the pathological lesion to the optic chiasm. In contrast, a homonymous visual field defect indicates damage to areas posterior to the optic chiasm, such as the optic tract, optic radiations, or primary visual cortex in the occipital lobe. When an afferent pupillary defect accompanies homonymous hemianopsia, it suggests that the lesion is localized to the optic tract.[2]  

Furthermore, homonymous hemianopsia with macular sparing suggests damage to the primary visual cortex. Macular sparing manifests as preservation of the central visual fields, ranging up to 25°. This finding is crucial as it signifies a posterior cerebral artery occlusion, mitigates the effect of hemianopia, and preserves the ability to read fluently. Two primary theories exist as to why macular sparing occurs.

Dual Representation of the Macula in Each Hemisphere

After the loss of an occipital lobe, the representation in the remaining occipital lobe preserves central vision in the blind hemifield. This phenomenon is supported by midline retinal ganglion cells projecting to the wrong hemisphere. These cells drive neurons in the striate cortex with ipsilateral receptive fields, forming the basis of this theory.[22]

Dual Perfusion Theory

A more widely accepted theory suggests that collateral flow from the middle cerebral artery preserves perfusion in the occipital pole, where the macula is represented, following occlusion of the posterior cerebral artery. Neuroimaging shows preservation of the occipital pole when macular sparing is present.[22]

In addition to severe deficits in their contralesional visual field, individuals with homonymous hemianopsia may demonstrate dissociations between perception and awareness, including:

• Anosognosia, where patients may lack awareness of their visual field defect.

• Unconscious visual abilities in the blind hemifield, also known as blindsight.

• Subtle deficits in the ipsilesional visual field, which the patients may be unaware of.

• Visual hallucinations, which may occur in the blind field of affected patients. However, the patients may be unaware that their perceptions are unreal.[23]

Evaluation

Testing Visual Fields

Confrontation: Confrontation testing is a simple and valuable method for assessing the visual field. This test is associated with a low sensitivity ranging from 35% to 74%. The below-mentioned steps should be followed to perform this examination.

• The patient is instructed to sit 1 to 2 feet away from the examiner.

• The patient is instructed to cover their left eye with their left hand.

• The patient fixates their right eye to look straight ahead at the examiner's left eye.

• If the patient does not maintain gaze, the examiner should remind the patient to focus on the examiner's left eye.

• The examiner closes their right eye.

• The examiner says, "I will present a moving finger on the edge of your vision and slowly bring it toward the center. As soon as you see movement, say 'yes.'"

• The presentation of a slowly wiggling finger from the periphery to the center, repeated in each quadrant, provides a sense of the exact location and shape of the visual field.

Formal visual field perimetry: Formal visual field perimetry testing is a crucial method for assessing the visual field with heightened sensitivity as it exceeds the limitations of confrontation testing alone.

• This testing method involves automated static perimetry and manual kinetic perimetry.

• This method offers increased sensitivity, providing detailed information about the type, size, and form of visual field loss.

• This method is considered essential for all patients with neurological lesions causing visual field defects. 

Evaluation of the Underlying Etiology

Neuroimaging combined with physical examination findings can characterize the cause of hemianopsia and guide clinical management. Individuals exhibiting focal neurological findings indicative of a stroke and falling within the intervention window should promptly undergo imaging following institutional protocols or the guidelines outlined by the American Heart Association/American Stroke Association for stroke management.

MRI with contrast of the brain is the preferred method for evaluating both bitemporal hemianopsia and homonymous hemianopsia. When assessing bitemporal hemianopsia, particular emphasis should be placed on examining the optic chiasm and sellar region. In addition, it is crucial to fully examine the retrochiasmal structures, such as the optic tract and occipital lobe, in people with homonymous hemianopsia. Diagnosing homonymous hemianopsia in children can be challenging due to their inability to comply with perimetry. Therefore, children typically undergo an MRI to identify lesions in the retrochiasmatic visual pathway.[24]

Diffusion-weighted imaging is the preferred method for detecting vasogenic edema associated with acute ischemic changes. Notably, in emergent scenarios, computed tomography (CT) may be used to evaluate for ischemia, mass lesions, or vascular aneurysms. In addition, a CT angiogram can be beneficial in large vessel pathologies, such as the middle cerebral artery or posterior cerebral artery occlusion.[25]

 Additional Testing

• Electroencephalography may be necessary to evaluate the possibility of an underlying seizure disorder.

• Laboratory testing can evaluate for hyperglycemia and immunoglobulin G4–related disease.
  • Renal function testing may be necessary before administering contrast for imaging studies.
  • Coagulation studies may be required before the administration of thrombolytics in the case of ischemic stroke.

• A lumbar puncture may be necessary to aid in the diagnosis of multiple sclerosis.

Treatment / Management

The findings from the physical examination and imaging studies should inform clinical management. Patients diagnosed with cerebral infarction or hemorrhage should receive tailored management. Consultation with neurology and neurosurgery is warranted when appropriate. Patients exhibiting mass lesions or signs of increased intracranial pressure may require hospital admission for medical or surgical therapy. 

Patients with visual field deficits may not be aware of the limitations imposed by their condition and might continue to drive. In the United States, each state has unique visual criteria that determine the legal eligibility for driving. The treating clinician is responsible for assessing if the patient meets these legal requirements and providing appropriate counseling on this matter.[26] The American Academy of Ophthalmology summarizes each state's vision requirement. Patient recovery can be enhanced through a comprehensive approach that includes visual training, visual assist devices, occupational therapy, and psychological services.[27] Activity-based interventions, such as visual scanning and compensatory training, have proven to be effective and are commonly utilized in the treatment of hemianopsia.[28](A1)

The objective of rehabilitation is to assist affected patients in adapting to their visual field deficits by enhancing attention and addressing any associated neglect. The techniques used in this process are mentioned below.

Compensation: Patients compensate by relying on their remaining intact function.

Substitution: Patients modify their environment to adapt to their functional limitations.

Restitution: Patients undergo training to redevelop impaired function.

Hemianopic mirrors or prisms can benefit individuals with stroke and homonymous hemianopia as they shift the peripheral image toward the central retinal meridian.[9] Peripheral prisms (p-prisms) expand the visual fields among patients with hemianopsia by shifting images from the blind hemifield onto the intact hemifield, thereby enhancing their ability to navigate hazards in the blind hemifield.[29] However, prisms can cause confusion and spatial distortion in some patients. Although they are suitable for ambulation, it is not advisable to use prisms for driving. 

Individuals experiencing challenges in reading due to homonymous hemianopsia may find it helpful to place a ruler or finger just under the text they are reading. In addition, learning to read vertically can be beneficial for certain individuals. Computerized saccadic training programs are specifically designed to help patients develop the ability to make small saccades or rapid movements into their blind field. The utilization of these programs has demonstrated improvements in reading times and a reduction in scanning errors for some individuals.

Restorative methods aim to broaden the visual field by stimulating the brain adjacent to the blind hemifield. Both animal and human studies suggest that visual-auditory stimulation therapy, leveraging the multisensory architecture of the brain, could effectively restore visual sensitivity in hemianopsia. Recent studies reveal that visual-auditory stimulation therapy may restore visual responsiveness in the neurons of the midbrain indirectly compromised by cortical lesions, leading to the restoration of contralesional space vision.[30] In a recent case study, individuals who underwent visual-auditory stimulation therapy regained the capacity to detect and articulate visual stimuli, determine their location, recognize certain features, and simultaneously perceive multiple visual stimuli in both fields. Multisensory therapy is a potentially fast and effective way to restore visual function in patients with hemianopia.[31][32] Some researchers suggest that the improvement is more likely associated with increased attention directed toward the edge of the blind field rather than an actual expansion of the visual field.

Biofeedback training effectively improves visual function and enhances the quality of life for individuals with homonymous hemianopia.[33] This therapy enhances oculomotor control and repositions the visual fields by altering the patient's fixation point. The improvements attributed to biofeedback therapy include enhanced visual acuity for distance and near vision, improved contrast sensitivity, increased retinal sensitivity, and enhanced reading speed.

Differential Diagnosis

The differential diagnosis of hemianopsia relates closely to the location and the underlying etiology. The following list contains the differential diagnoses for hemianopsia:

• Cerebral infarction
• Intracranial hemorrhage
• Saccular aneurysm
• Mass lesions, including primary and metastatic tumors
• Pituitary adenoma
• Craniopharyngioma
• Meningioma
• Central nervous system lymphoma or other primary malignancy
• Altitudinal hemianopia
• Trauma
• Inflammatory conditions, including demyelinating disorders
• Severe hyperglycemia
• Degenerative neurological conditions 
• Migraine
• Transient ischemia attack
• Seizure or status epilepticus [34]
• Immunoglobulin G4–related disease [35]

Prognosis

Visual loss in the setting of stroke suggests a poor prognosis, with the rate of improvement ranging widely from 17% to 67%. Certain studies indicate that only 18% of patients with homonymous hemianopsia regain their vision within 28 to 30 days of the inciting event. In contrast, others report spontaneous improvement in 46% to 67% of cases within 1 month of an ischemic stroke.[36][37][38] The chances of visual recovery diminish over time, with the likelihood of regaining visual function notably low after 6 months.[27][39] 

Patients with bitemporal hemianopsia attributed to pituitary tumors typically experience visual field improvement in 79% to 95% of cases following resection. However, the extent of recovery may hinge on factors such as retinal nerve fiber layer thickness, preoperative deficit severity, duration of visual symptoms, tumor size, extent of resection, and patient age.[40]

A recent study explores the adaptation process of patients to post-stroke hemianopsia visual field loss by closely monitoring early-stage adaptation. The results highlight that adaptation to hemianopsia is individualized and influenced by factors such as the outcomes of a mobility assessment course (MAC) and the degree of inferior visual field loss. The authors recommend incorporating MAC as an assessment tool for evaluating mobility and scanning during rehabilitating patients with homonymous hemianopsia.[41][42]

Complications

Complications associated with hemianopsia, including impaired balance, heightened risk of falls and injury, loss of independence, reading difficulties, impaired visual scanning, increased risk of depression, and reduced employment opportunities, can significantly impact the quality of life in patients.