The caudal part of the middle frontal gyrus (part of Brodmann's area 8) is concerned with voluntary eye movements and is independent of visual stimuli. If the lesion is
1. Irritative, that is, epileptic seizure, the eyes and head will turn to the opposite side. This phenomenon has been reproduced experimentally, although the direction of the turn is not to the opposite side 100% of the time.
2. Destruction of the frontal cortex or its connections through the internal capsule, the eyes are forced, by the opposite healthy cortex, to the side of the lesion and away from the side of the paretic arm and leg. As the lesion becomes chronic, the eyes will again be in the primary position and will move to the side of the lesion, but for a time will not cross the midline to the side of the paretic arm and leg. In short, the stroke patient will not look toward his paretic arm and leg, whereas the convulsing patient must look toward his twitching arm and leg (usually).
To determine that the lesion is in the hemisphere and not the brain stem,
• Rapidly turn the patient's head to the side of the normal arm and leg and you will see her eyes move conjugately to the side of the paresis (this is the doll's eye test; see the section on "The Doll's Eye Test and Caloric Testing").
• Irrigate the external auditory canal on the side of the abnormal arm and leg with cold water and the eyes will deviate to that side (see the section on examination of the eighth cranial nerve in Chapter 9).
• If the patient is alert enough to cooperate, have her fix her gaze at your finger (or her own) about 0.5 m in front of her. Ask her to keep staring at the finger as you rotate her head away from her paretic arm and leg. If the eyes stay fixed on the stationary finger, they will conjugately move to the side of the hemiparesis.
If the cause of the gaze palsy is in the brain stem, these three procedures will not produce conjugate gaze movement.
It is often difficult to tell whether a patient has a conjugate gaze palsy to one side of the midline, or a hemianopic field defect on the same side (he may have both; see the following section on the occipital eye center).The difficulty may be compounded because the patient is obtunded or dysphasic or both.
The presence of a field defect can be inferred by the following method:
• Bring your hand rapidly up to the patient's eyes from the side of his head in a threatening gesture.
• If he consistently blinks when the hand comes from one side but not from the other, he is probably hemianopic on the latter.
• If he blinks on both sides, he has a gaze palsy only and full visual fields.
Patients with conjugate gaze palsy from vascular disease of the anterior gaze "center" or its connections usually recover full eye movements. The recovery of the gaze palsy is usually much better than recovery of the paretic arm and leg.
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