Bitemporal Hemianopia

Bitemporal hemianopia is a specific pattern of vision loss affecting the outer (temporal) visual fields of both eyes. It occurs when the optic chiasm—where the optic nerves cross—is compressed, typically by a pituitary tumor or other lesion at the base of the brain.

Understanding the Anatomy

At the optic chiasm, nerve fibers from the inner (nasal) half of each retina cross to the opposite side. These fibers carry information from the temporal (outer) visual fields.

When the chiasm is compressed from below (as with a pituitary tumor), these crossing fibers are damaged first, causing loss of both temporal visual fields.

What Patients Experience

• "Tunnel vision" or narrowed peripheral vision
• Bumping into things on the sides
• Difficulty seeing cars approaching from the side while driving
• May not notice the problem until significant
• Often discovered on routine visual field testing

Common Causes

Pituitary Adenoma

• Most common cause
• Tumor grows upward from pituitary gland
• Compresses chiasm from below
• See Pituitary Tumor

Other Causes

• Craniopharyngioma—benign tumor near pituitary
• Meningioma—tumor of the meninges
• Aneurysm—of nearby blood vessels
• Empty sella syndrome
• Chiasmal glioma—tumor of the optic chiasm

Diagnosis

Visual Field Testing

• Visual field test shows characteristic pattern
• Defects respect the vertical midline
• May be asymmetric between the two eyes
• "Junction scotoma" if optic nerve also affected

Brain Imaging

• MRI brain with contrast
• Shows the lesion compressing the chiasm
• Helps identify the specific cause
• May need MRI of pituitary with specialized protocol

Endocrine Testing

If pituitary tumor suspected:

• Prolactin level
• Growth hormone/IGF-1
• Thyroid function
• Cortisol levels
• Other pituitary hormones

Treatment

Treatment depends on the underlying cause:

Pituitary Adenoma

• Dopamine agonists for prolactinomas
• Transsphenoidal surgery for other types
• Radiation therapy in some cases
• See Pituitary Tumor

Other Lesions

• Surgery for accessible tumors
• Radiation for some lesions
• Monitoring for slow-growing tumors

Visual Prognosis

• Early treatment often leads to improvement
• Vision may recover significantly if compression relieved
• Recovery depends on:
  • Duration of compression
  • Severity of damage
  • Speed of treatment
• Some permanent loss may remain

Living with Bitemporal Hemianopia

Driving Considerations

• May not be safe to drive
• Check with your state's requirements
• Some patients can drive with adaptations

Daily Adaptations

• Turn head more to scan periphery
• Be extra careful crossing streets
• Use mirrors strategically at home
• Good lighting important