From the Research
A lesion in the right optic tract causes a left homonymous hemianopia, meaning vision loss in the left half of the visual field in both eyes. This occurs because the right optic tract carries visual information from the left visual field of both eyes after the fibers have partially crossed at the optic chiasm. Specifically, the right optic tract contains fibers from the temporal (lateral) retina of the right eye and the nasal (medial) retina of the left eye, both of which receive input from the left visual field. Patients with this condition typically have difficulty seeing objects in their left peripheral vision and may bump into objects on their left side. They often compensate by turning their head to the left to bring objects into their intact right visual field. Unlike lesions before the optic chiasm, which cause monocular vision loss, or lesions at the chiasm, which cause bitemporal hemianopia, tract lesions produce this characteristic homonymous (same-sided) visual field defect. The deficit is typically congruous, meaning the pattern of visual field loss is similar in both eyes, though it may be incongruous if the lesion is partial or anterior in the tract.
Clinical Presentation
The clinical presentation of a lesion in the right optic tract can vary depending on the underlying cause, but common symptoms include:
- Vision loss in the left half of the visual field in both eyes
- Difficulty seeing objects in the left peripheral vision
- Bumping into objects on the left side
- Compensatory head turning to bring objects into the intact right visual field
Diagnosis
Diagnosis of a lesion in the right optic tract can be made using a combination of clinical examination, imaging studies, and visual field testing. The most recent study on the topic, 1, suggests that a systematic approach to diagnosis, including visual field testing, optical coherence tomography (OCT), and magnetic resonance imaging (MRI), can help simplify the diagnosis of optic tract lesions.
Prognosis
The prognosis for patients with a lesion in the right optic tract depends on the underlying cause and the extent of the lesion. In some cases, such as those caused by multiple sclerosis, the visual field defect may be reversible with treatment 2. In other cases, the defect may be permanent. The study by 3 highlights the importance of considering neurosyphilis as a potential cause of optic tract lesions, and the potential for reversal of the visual field defect with treatment.
Key Points
- A lesion in the right optic tract causes a left homonymous hemianopia
- The deficit is typically congruous, but may be incongruous if the lesion is partial or anterior in the tract
- Diagnosis can be made using a combination of clinical examination, imaging studies, and visual field testing
- Prognosis depends on the underlying cause and the extent of the lesion.