In a cranial nerve exam, what does a rightward gaze deviation indicate?

In a cranial nerve exam, a rightward gaze deviation suggests that there may be dysfunction in the left hemisphere of the brain. This is due to the way the brain controls eye movements. The frontal eye fields, located in the frontal lobe, are responsible for initiating horizontal gaze. When a person gazes to the right, the right eye is controlled by the right hemisphere and the left eye is controlled by the left hemisphere. If gaze deviation occurs to the right, it can indicate that the left hemisphere is not functioning properly or that there is some dysfunction in the neural pathways that control the left eye’s movement towards the right.

This phenomenon occurs because the left hemisphere generally exerts an inhibitory effect on the right hemisphere when it comes to controlling eye movements. Thus, if there is an issue on the left side (such as a stroke or lesion), the left eye may not move appropriately, leading to a rightward gaze deviation, reflecting underlying left-sided brain dysfunction.