Hemianopia

Hemianopia is a loss of half of the visual field in one or both eyes. The most common form is homonymous hemianopia, in which the same half of the field is missing in each eye. It results from damage to the post-chiasmal portions of the visual pathways, including the optic tract, optic radiations, or occipital cortex.

Types and presentation: Homonymous hemianopia causes loss of the same side of the visual field in both eyes (left or right). It can be complete or partial and may spare the macula (macular sparing) in some cases due to the dual blood supply of the occipital cortex. Heteronymous (bitemporal) hemianopia, caused by lesions at the optic chiasm such as pituitary tumors, produces loss of the outer (temporal) fields in both eyes. Quadrantanopia refers to loss of a quarter of the field and arises from focal damage to the optic radiations, producing pie-in-the-sky (superior) or pie-on-the-floor (inferior) defects.

Causes: The most common cause is a stroke (ischemic or hemorrhagic) affecting the post-chiasmal pathways. Other causes include traumatic brain injury, brain tumors, demyelinating diseases such as multiple sclerosis, infections, or complications from neurosurgery.

Symptoms and impact: Patients notice loss of peripheral vision on one side, which can affect navigation, reading, and daily activities. The defect may be underrecognized initially and can raise safety concerns, including driving eligibility in many jurisdictions.

Diagnosis: Evaluation involves a detailed eye examination and visual field testing (confrontation, automated perimetry like Humphrey or Goldman). Neuroimaging (MRI or CT) localizes the lesion, and neurological assessment guides management.

Management: Treatment targets the underlying cause and, where possible, restoration of function. Rehabilitation includes compensatory visual-scanning training, mobility strategies, and, in selected cases, prism glasses. Prognosis varies with lesion location and size; partial recovery may occur, especially after stroke, but complete restoration is uncommon.