Control of Horizontal Gaze

Horizontal gaze is controlled by two interconnected gaze centers. One control center is in the frontal lobe, the frontal eye field (Brodmann area 8). This area acts as a center for contralateral horizontal gaze. In the pons is a second gaze center, known as the pontine gaze center or the PPRF, the paramedial pontine reticular formation. This is a center for ipsilateral horizontal gaze. When activated by neurons in the frontal eye field, the pontine gaze center neurons send axons to synapse with cell bodies in the abducens nucleus, which is actually contained within the pontine gaze center. The pontine gaze center also sends axons that cross immediately and course in the contralateral MLF to reach the contralateral oculomotor nucleus. The net effect of stimulation of the left frontal eye field, therefore, is activation of the pontine gaze center on the right and a saccadic horizontal eye movement of both eyes to the right. Horizontal gaze to the right results from activation of the right abducens nucleus and the left oculomotor nucleus by fibers in the MLF. Lesions in the MLF result in an internuclear ophthalmoplegia in which there is an inability to adduct one eye on attempted gaze to the opposite side. For example, a lesion in the right MLF results in an inability to adduct the right eye on an attempted gaze to the left. The left eye abducts normally but exhibits a nystagmus. If the MLF is lesioned bilaterally (as might be the case in multiple sclerosis), neither eye adducts on attempted gaze (Figures IV-5-11 and IV-5-12), and the abducting eye exhibits a nystagmus.

Horizontal Eyer Gaze

Figure IV-5-10. Voluntary Horizontal Conjugate Gaze

Ask patient to look to the right - response shown below

Ask patient to look to the right - response shown below

Control Horizontal Gaze

Figure IV-5-11. Normal and Abnormal Horizontal Gaze

Table IV-5-2. Normal and Abnormal Responses to the Horizontal Conjugate Gaze: Part 1

Lesion location

Symptoms (Results)

Right Abducens nerve, #1 Right Abducens nucleus, #2

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Right eye cannot look right (abduct)

Neither eye can look right (lateral gaze paralysis)—-may be slow drift left and right fecial paralysis

Ask patient to look to the right - response shown below

Ask patient to look to the right - response shown below

Gaze Paralysis
Figure IV-5-12. Normal and Abnormal Horizontal Gaze
Table IV-5-3. Normal and Abnormal Responses to the Horizontal Gaze: Part 2

Location

Symptoms (Results)

Left cerebral cortex, #4

Left eye cannot look right; convergence intact; right eye exhibits nystagmus

Neither eye can look right: but slow drift to left

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