Hemianopsia

Hemianopsia is a defect of vision in which half of the visual field is lost. The most common form is homonymous hemianopsia, where the same half of the field is missing in both eyes, typically due to a lesion in the retrochiasmal visual pathways located behind the optic chiasm (in the optic radiations or the occipital cortex). Less common are heteronymous defects, such as bitemporal hemianopsia caused by chiasmal compression, where the outer (temporal) halves are lost in both eyes.

Causes are primarily neurological and include stroke or other lesions in the posterior cerebral artery territory, brain tumors, traumatic brain injury, infections, and demyelinating diseases. The pattern of field loss usually corresponds to the location of the lesion, with occipital or optic radiations damage producing contralateral homonymous hemianopsia; macular sparing can occur with some occipital lesions due to dual blood supply to the macula.

Symptoms commonly involve reduced or missing vision in the affected half of the visual field, which may lead to difficulty with reading, navigating, or perceiving objects on the affected side. Some individuals may develop compensatory scanning habits, and visual neglect can accompany lesions in the parietal cortex.

Diagnosis relies on visual field testing, such as automated perimetry, along with imaging studies (MRI or CT) to identify the underlying brain lesion. Management focuses on treating the underlying cause when possible and on rehabilitation to improve functional use of the remaining vision, including visual scanning training and, in some cases, prism glasses or other aids to expand functional field. Prognosis varies with etiology and extent of brain damage.