Binasal hemianopsia

Binasal Hemianopsia is a visual field defect characterized by the loss of vision in the nasal (inner) halves of both eyes. This condition is relatively rare and can result from various causes, including neurological disorders, brain lesions, or damage to the optic chiasm. Understanding binasal hemianopsia requires a grasp of the anatomy of the visual pathways and the potential pathologies that can affect them.

Causes

Binasal hemianopsia arises when there is an interruption in the visual pathway, specifically affecting the fibers that transmit visual information from the temporal (outer) fields of vision. The causes can be broadly categorized into:

• Optic chiasm lesions: The optic chiasm is where the optic nerves from each eye cross. Lesions here, such as those caused by pituitary adenomas, can compress the uncrossed fibers, leading to binasal hemianopsia.
• Neurological disorders: Conditions such as multiple sclerosis or stroke can affect the brain areas or pathways responsible for processing visual information.
• Trauma: Direct injury to the optic chiasm or the brain can disrupt the visual pathways.
• Intracranial pressure: Increased pressure inside the skull, often due to tumors, can compress the optic chiasm or related structures.

Symptoms

The primary symptom of binasal hemianopsia is the loss of vision in the inner half of both eyes. This can lead to difficulties with activities that require a wide field of vision, such as driving. Patients may also experience:

• Headaches
• Difficulty reading
• Bumping into objects on their sides
• Visual hallucinations in rare cases

Diagnosis

Diagnosis of binasal hemianopsia involves a comprehensive eye examination, including:

• Visual field test: This test measures the entire scope of vision, including peripheral vision, to identify any blind spots.
• Magnetic resonance imaging (MRI): An MRI can help identify any lesions or abnormalities in the brain or along the visual pathways.
• Computed tomography (CT) scan: A CT scan can also be used to detect structural abnormalities causing the condition.

Treatment

Treatment for binasal hemianopsia focuses on addressing the underlying cause. This may include:

• Surgery: If a tumor or lesion is compressing the optic chiasm, surgery may be necessary to remove it.
• Radiation therapy: For tumors that cannot be surgically removed, radiation therapy may be used to reduce their size.
• Medication: Medications can help manage symptoms or treat underlying conditions, such as multiple sclerosis.

Prognosis

The prognosis for binasal hemianopsia varies depending on the underlying cause. If the condition is caused by a treatable issue, such as a benign tumor, vision may partially or fully recover after treatment. However, if it results from permanent damage to the visual pathways, the vision loss may be irreversible.

See also

• Visual field test
• Optic chiasm
• Pituitary adenoma
• Multiple sclerosis
• Stroke