Which visual fields are affected with left homonymous hemianopia (half vision loss)?

Visual Fields Affected in Left Homonymous Hemianopia

In left homonymous hemianopia, the right half of the visual field in both eyes is affected, resulting in loss of vision in the right visual field of each eye. 1

Anatomical Understanding

Left homonymous hemianopia occurs due to damage to the visual pathway posterior to the optic chiasm on the right side of the brain. This creates a characteristic pattern of visual field loss:

• The right half of the visual field is lost in both eyes
• The vertical midline of vision is typically preserved
• The defect is "homonymous" meaning it affects the same side of vision in both eyes
• The defect is "hemianopic" meaning it affects half of the visual field

Clinical Characteristics

The visual field defect in left homonymous hemianopia may present in several forms:

• Complete hemianopia: The entire right half of the visual field is lost in both eyes
• Incomplete hemianopia: Partial loss of the right visual field, which may include:
  • Quadrantanopia: Loss of a quarter of the visual field (upper or lower right quadrant)
  • Scotomatous defects: Isolated blind spots in the right visual field
  • Partial hemianopia: Incomplete loss of the right visual field
  • Hemianopia with macular sparing: The central vision (macula) is preserved despite peripheral field loss 2

Functional Implications

Patients with left homonymous hemianopia experience specific functional challenges:

• Difficulty seeing objects in the right visual field
• Bumping into objects on the right side
• Reading problems, particularly difficulty finding the beginning of the next line of text (as opposed to right-sided hemianopia where patients struggle with seeing the ends of words) 1
• Many patients may be unaware of their visual field defect, which can lead to safety concerns 3

Common Causes

The most common causes of homonymous hemianopia include:

• Stroke (69.6% of cases) - most common cause
• Traumatic brain injury (13.6%)
• Brain tumors (11.3%)
• Neurosurgical procedures (2.4%)
• Demyelinating diseases like multiple sclerosis (1.4%) 2, 4

Anatomical Localization

While left homonymous hemianopia indicates damage to the right side of the visual pathway, the specific location can vary:

• Occipital lobe (45% of cases)
• Optic radiations (32.2%)
• Optic tract
• Lateral geniculate nucleus 2

It's important to note that the specific configuration of the visual field defect does not always reliably predict the exact location of the lesion within the retrochiasmal visual pathway 4.

Clinical Pitfalls to Avoid

• Don't assume all homonymous hemianopias are caused by stroke - while stroke is the most common cause (69.7%), other etiologies like trauma and tumors are significant 4
• Don't overlook left homonymous hemianopia as it can be an unrecognized symptom of serious underlying conditions like brain tumors 3
• Don't confuse homonymous hemianopia with heteronymous hemianopia (which affects opposite halves of the visual fields in both eyes, such as bitemporal or binasal hemianopia) 5