Bitemporal hemianopia

Bitemporal hemianopia is a form of visual field loss that affects the outer (temporal) halves of the visual field in both eyes, with the central and nasal (inner) visual fields remaining intact. This condition is characterized by the loss of peripheral vision on the same side in both eyes. It is most commonly associated with lesions or abnormalities affecting the optic chiasm, the area where the optic nerves partially cross. Bitemporal hemianopia is an important diagnostic clue in neuro-ophthalmology and can indicate various underlying neurological conditions.

Causes

The primary cause of bitemporal hemianopia is damage to or compression of the optic chiasm. Several conditions can lead to this, including:

• Pituitary adenoma: A benign tumor of the pituitary gland, which is located directly below the optic chiasm. These tumors can grow upwards and compress the chiasm.
• Craniopharyngioma: Another type of benign tumor that can compress the optic chiasm.
• Meningioma: Tumors that arise from the meninges, the membranes that cover the brain and spinal cord, which can also compress the optic pathways.
• Aneurysm: Swelling of a blood vessel that can press on the optic chiasm.
• Trauma: Injury to the head can damage the optic chiasm directly or cause bleeding that compresses it.
• Multiple sclerosis: A disease that affects the central nervous system can lead to lesions on the optic chiasm.

Symptoms

Patients with bitemporal hemianopia typically report difficulty with peripheral vision, which can manifest as bumping into objects, difficulty navigating in crowded or unfamiliar places, and a narrowed field of view, often described as "tunnel vision." However, central vision remains unaffected, allowing for relatively normal reading and other activities that require looking straight ahead.

Diagnosis

Diagnosis of bitemporal hemianopia involves a comprehensive eye examination, including:

• Visual field test: A test that measures the entire scope of vision, including peripheral vision, to identify any areas of vision loss.
• Magnetic resonance imaging (MRI) or Computed tomography (CT) scan: Imaging tests that can identify abnormalities or lesions on the optic chiasm.
• Ophthalmoscopy: Examination of the back of the eye to check for any optic nerve abnormalities.

Treatment

Treatment for bitemporal hemianopia focuses on addressing the underlying cause of the optic chiasm compression. This may include:

• Surgery: To remove or reduce the size of tumors pressing on the optic chiasm.
• Radiation therapy: Especially for tumors that are not completely resectable.
• Medication: To reduce tumor size or manage other conditions affecting the optic chiasm.

In some cases, vision loss from bitemporal hemianopia may be permanent. Patients may benefit from low vision rehabilitation to learn strategies for coping with their vision loss.

Prognosis

The prognosis for bitemporal hemianopia largely depends on the underlying cause and the timeliness of treatment. Early detection and treatment of conditions causing compression of the optic chiasm can improve the chances of recovering vision or preventing further vision loss.