From the Guidelines
A 62-year-old patient with right-sided homonymous hemianopsia most likely has a lesion affecting the left optic tract or left occipital lobe, as evidenced by the symptoms and signs of neurological deficit persisting longer than 24 hours, which is characteristic of ischemic stroke 1. The visual field defect occurs when there is damage to the visual pathway posterior to the optic chiasm, specifically affecting the visual fibers that carry information from the right visual field of both eyes.
- The most common location for such a lesion is the left occipital lobe (primary visual cortex), though it could also occur in the left optic tract or left optic radiations.
- The pattern is "homonymous" because it affects the same side of the visual field in both eyes. This type of visual field defect is often caused by stroke, tumor, trauma, or other focal neurological damage, with stroke being a primary consideration given the patient's age, as symptoms and signs that result from ischemia or infarction in the distribution of the left internal carotid artery or middle cerebral artery may cause right-sided weakness, right-sided paresthesia or sensory loss, aphasia, and monocular blindness that affects the left eye or left visual field, including right homonymous hemianopsia 1. The left-sided lesion causes right-sided visual field loss due to the crossing of nasal retinal fibers at the optic chiasm, resulting in contralateral visual field defects. Given the patient's age, vascular causes such as stroke should be considered as a primary etiology, and urgent neuroimaging (MRI brain) would be indicated to identify the precise location and cause of the lesion, as the symptoms and signs of neurological deficit persisting longer than 24 hours are characteristic of ischemic stroke, which is a medical emergency requiring prompt attention 1.
From the Research
Lesion Location in Homonymous Hemianopsia
The patient's condition, right-sided homonymous hemianopsia, indicates a visual field defect involving the right halves of the visual field of both eyes. This condition results from damage to the visual pathway in its suprachiasmatic part 2.
Possible Causes and Locations
The causes of homonymous hemianopsia include stroke, brain tumors, head injuries, neurosurgical procedures, multiple sclerosis, and miscellaneous conditions 2, 3, 4. The configuration of the homonymous hemianopsia does not predict where in the retrochiasmal visual pathway the responsible lesion lies 3.
Specific Nerve or Tract Involved
Given that the visual pathway is damaged in its suprachiasmatic part, the lesion is likely to affect the optic tract, the lateral geniculate nucleus, or the visual cortex in the occipital lobe, as these are parts of the retrochiasmal visual pathway 3, 4.
Key Points to Consider
- Homonymous hemianopsia results from damage to the visual pathway in its suprachiasmatic part.
- The optic tract, lateral geniculate nucleus, or visual cortex in the occipital lobe could be the site of the lesion.
- Stroke is a common cause of homonymous hemianopsia, particularly in adults 3, 4, 5, 6.
- The prognosis and management of homonymous hemianopsia depend on the cause and severity of the brain and optic pathway injury 2, 4.