Johnny Silva Cancer Research

Ocular Tilt Reaction

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A unilateral interruption of the otolithic afferent pathway causes the ocular tilt reaction (OTR), which has four components:

1. A yoked rotational displacement of both eyes around the visual axis

2. A vertical strabismus (skew deviation)

3. A head tilt to one side

4. A tilt of the subjective visual perception of the vertical

All four components are tilted in the same direction. (In the example diagrammed in ■ Fig. 11.8, the tilt is to the right.)

The rotational displacement of both eyes and the skew deviation are caused by an interruption of the otolithic signal to the superior rectus of the ipsilateral eye and the inferior oblique of the contralateral eye (■ Fig. 11.8). The head tilt arises from a defective projection to the neck muscles and the tilt of the subjective visual vertical is caused by a faulty projection to the vestibular cortex. The cyclodevia-tion and the tilt of the subjective visual vertical are in the same direction in both eyes, but their magnitudes can differ. A lesion of the otolithic pathway in the caudal brain-stem (medulla oblongata or caudal pons) will cause a tilt to

Fig. 11.8. Graviceptive pathway. With a lesion of the pathway that carries the input signal from the right otolithic apparatus to the ocular motor nuclei, an "ocular tilt reaction" (OTR) to the right is produced

the ipsilateral side, whereas a lesion damaging the same path in the more rostral portions of the brainstem (rostral pons or midbrain) will cause a tilt to the opposite side. This reversal of direction at the mid pons is due to a decussation of the otolithic pathways in the pons (■ Fig. 11.8).

The rotational displacement of both eyes around their visual axes can be seen in the rotational orientation of the line between the optic disc and the fovea. Fundus photography is the preferred medium for documentation. Alternatively, the position of the physiologic blind spot relative to the horizontal meridian can be plotted with kinetic pe-rimetry. Ordinarily, the center of the optic disc lies about 2° above, and the center of the blind spot lies 2° below the horizontal meridian. This corresponds to a rotation of about 7°. The subjective visual vertical (and the subjective horizontal, i.e., the entire image) appears tilted in the same direction, as is the cyclodeviation of the eyes around their visual axes, though not always to the same extent. The subjective visual vertical should be determined by letting the patient adjust a narrow streak of light in a darkened room under monocular observation. The rotational orientation of the streak then measures the error in the subjective visual vertical.

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