What is homonymous hemianopia and what are its causes?

From the Guidelines

Homonymous hemianopia is a visual field defect where a person loses vision in the same half of both eyes, either the right or left side, most commonly caused by stroke, traumatic brain injury, brain tumors, and neurosurgical procedures that affect the posterior visual pathway. This condition occurs due to damage to the visual pathway behind the optic chiasm, specifically in the optic tract, lateral geniculate nucleus, optic radiation, or visual cortex in the occipital lobe 1. The causes of homonymous hemianopia can be summarized as follows:

• Stroke: accounting for about 70% of cases
• Traumatic brain injury
• Brain tumors
• Neurosurgical procedures that affect the posterior visual pathway
• Less frequently, it can result from multiple sclerosis, brain infections, or degenerative disorders such as Parkinson’s disease and multiple sclerosis 1. The condition occurs because visual information from both eyes crosses and is organized in the brain such that damage to one side of the posterior visual pathway affects the opposite half of the visual field in both eyes. For example, damage to the right occipital lobe results in left-sided vision loss in both eyes. Patients often experience difficulties with reading, navigation, and driving, and may bump into objects on their affected side. Recovery is possible in some cases, particularly when caused by stroke, with approximately 50% of patients showing some improvement within the first few months 1.

Some of the key challenges faced by patients with homonymous hemianopia include:

• Difficulty reading, with right hemianopia causing difficulty seeing the end of longer words and impairs the ability to see subsequent words, thus disrupting the reading saccade pattern, and left hemianopia causing difficulty identifying the beginning of the next line of text 1
• Decreased accuracy and reading speed
• Difficulty with navigation and driving
• Increased risk of bumping into objects on their affected side Practical strategies such as marking the left margin of text or tilting text vertically can assist with reading, and there is limited evidence that practice reading laterally scrolling text improves reading for patients with hemianopia 1.

From the Research

Definition of Homonymous Hemianopia

• Homonymous hemianopia (HH) is a visual impairment that results from damage to visual pathways posterior to the optic chiasm 2.
• It is characterized by the loss of the same half of the visual field in both eyes, which can significantly impair daily activities such as driving, reading, and safe navigation 3.

Causes of Homonymous Hemianopia

• The primary cause of homonymous hemianopia is damage to the visual pathways in the brain, which can occur due to stroke, traumatic brain injury, or other neurological conditions 2, 4.
• The damage can affect the optic tract, lateral geniculate body, or the visual cortex, leading to impaired visual function 4.

Rehabilitation and Treatment

• Various rehabilitation approaches have been developed to improve visual function in patients with homonymous hemianopia, including:
  • Optical devices, such as prism glasses, to expand or relocate the affected visual field 5.
  • Compensatory training, such as eye movement training, to improve explorative saccades 6, 3.
  • Visual field restitution, which aims to improve visual processing within the damaged field itself 6, 4.
• These approaches have shown modest improvements with repeated practice, but none have been proven to be clearly superior to the rest 3.