Which area of the brain is likely affected in a patient presenting with double vision and preserved tracking but lacking horizontal eye movements?

The brainstem is the most plausible area affected in a patient presenting with double vision and preserved tracking but lacking horizontal eye movements. The brainstem is critical for the coordination of eye movements, including the pathways that govern horizontal gaze. Specifically, it houses the nuclei for cranial nerves that control eye movement, including the abducens nerve (cranial nerve VI), which is responsible for lateral eye movement.

In this case, double vision suggests a disruption in the coordination of the muscles responsible for eye alignment, and the inability to make horizontal eye movements indicates that a specific neurological pathway related to these movements is compromised. The presence of preserved tracking suggests that other aspects of eye movement control, possibly mediated by different pathways or areas, are intact. This impairment aligns with lesions or dysfunctions in the brainstem, which can result from various conditions such as strokes, tumors, or demyelinating diseases.

The other areas listed—frontal lobe, occipital lobe, and cerebellum—are less likely to be involved in this specific presentation. The frontal lobe primarily contributes to voluntary eye movements and executive function, while the occipital lobe is mainly responsible for visual processing. The cerebellum plays a key role in coordination and balance,