From the Guidelines
Optic tract lesions are associated with homonymous bilateral field defects, including homonymous hemianopsia, quadrantanopia, and altitudinal field defects, as evidenced by the most recent study in 2023 1. These types of blindness result from damage to the optic tract, which contains fibers from both eyes representing the contralateral visual field. The main characteristics of these visual field defects include:
- Homonymous hemianopsia: loss of vision in the same half of the visual field in both eyes, opposite to the side of the lesion
- Quadrantanopia: loss of vision in a quarter of the visual field
- Altitudinal field defects: loss of vision in the upper or lower half of the visual field According to the vision rehabilitation preferred practice pattern 1, these defects can be classified using ICD-10 CM codes, including H53.461 for homonymous bilateral field defects in the right eye and H53.462 for homonymous bilateral field defects in the left eye. Key points to consider in the diagnosis and management of optic tract lesions include:
- Visual field testing to confirm the presence and extent of the visual field defect
- Neuroimaging to identify the underlying cause of the lesion, such as tumors, vascular events, or demyelinating diseases
- Potential for relative afferent pupillary defect (RAPD) in the contralateral eye due to asymmetric distribution of crossed and uncrossed fibers.
From the Research
Types of Blindness Associated with Optic Tract Lesions
- Incongruous homonymous hemianopia is a common type of blindness associated with optic tract lesions, as reported in studies 2, 3, 4, 5
- Highly incongruous hemianopia can be diagnosed in the presence of an afferent pupillary defect and characteristic atrophy of the optic discs 2
- Complete homonymous hemianopia can also occur in optic tract lesions, with characteristic optic atrophy and retinal nerve fiber bundle defect, and relative afferent pupillary defect (RAPD) 6
- Bow-tie atrophy can be observed in patients with optic tract lesions, as reported in a study 4
- Incongruous homonymous hemianopia on visual field (VF) with corresponding hemianopic thinning on ganglion cell complex (GCC) can develop within months of optic tract lesions 3
Diagnostic Features
- Afferent pupillary defect and characteristic atrophy of the optic discs can be used to diagnose optic tract lesions 2
- Relative afferent pupillary defect (RAPD) can be helpful in differentiating optic tract lesions from suprageniculate lesions in cases of complete homonymous hemianopia 6
- Optical coherence tomography (OCT) of the peripapillary retinal nerve fiber layer (RNFL) can show horizontal thinning in the contralateral eye 4
- Magnetic resonance imaging (MRI) can reveal the location and extent of optic tract lesions 4