Cranial Nerves III, IV, VI
Eye Movements
BACKGROUND
Eye movements can be divided into four types:
The sites of control of these eye movements differ (Fig. 9.1).
| Type of eye movement | Site of control |
| Saccadic (command) | Frontal lobe |
| Pursuit | Occipital lobe |
| Vestibular–positional | Cerebellar vestibular nuclei |
| Convergence | Midbrain |
In the brainstem, the inputs from the frontal and occipital lobes, the cerebellum and the vestibular nuclei are integrated so that both eyes move together. Important structures are the centre for lateral gaze in the pons and the medial longitudinal fasciculus (MLF), which runs between the nuclei of the III and IV cranial nerves (in the midbrain) and the VI (in the pons).
Figure 9.1 Control of eye movements
The III, IV and VI cranial nerves then control the following muscles (Fig. 9.2):
Abnormalities can arise at any level (Fig. 9.1):
Figure 9.2 Muscles involved in eye movement
No double vision (generally):
Double vision:
Internuclear and supranuclear lesions rarely cause double vision.
WHAT TO DO
Look at the position of the head.
Look at the eyes.
• Note ptosis (see Chapter 6).
• Note the resting position of the eyes and the position of primary gaze.
Look at the position of the eyes in primary gaze.
Perform the cover test (Fig. 9.3).
Figure 9.3 The cover test. For an explanation, see text
The cover test
What to do
This is a test for latent squint.
