Examine / Motility Lab
Six muscles. Three nerves. Nine positions.
Move the eye through the positions of gaze, light each muscle in its field of action, and then examine three patients with a cranial nerve palsy: the eye will not go where the dead muscle would have taken it, and it rests where the survivors leave it.
Reconstructing the eye
Right eye · patient's right is on your left
Full movements
Muscles: choose one to test it in its field of action
The globe turns in its socket; the muscles are drawn at rest and do not shorten. A palsy is shown as the range the eye can reach and where it rests, as the clinic sees it.
Palsies
A 30-year-old with no double vision, for comparison.
The muscles
| Muscle | Nerve | Actions |
|---|---|---|
| Lateral rectus | Abducens (CN VI) | Abduction |
| Medial rectus | Oculomotor (CN III) | Adduction |
| Superior rectus | Oculomotor (CN III), superior division | Elevation; intorsion, adduction |
| Inferior rectus | Oculomotor (CN III), inferior division | Depression; extorsion, adduction |
| Superior oblique | Trochlear (CN IV) | Intorsion; depression (in adduction), abduction |
| Inferior oblique | Oculomotor (CN III), inferior division | Extorsion; elevation (in adduction), abduction |
LR6 SO4, the rest 3: the lateral rectus is the sixth nerve, the superior oblique the fourth, everything else the third.
Examining eye movements
- 01Look first: a head tilt or turn, a ptosis, a squint in the primary position, the corneal light reflexes.
- 02Cover test: cover one eye and watch the other for a refixation movement (a tropia); uncover and watch the covered eye (a phoria).
- 03Ductions and versions: follow a target through the nine positions of gaze, one eye covered then both, and ask where the double vision is worst.
- 04Which images? Horizontal, vertical or oblique; whether they separate more in one gaze; whether closing either eye abolishes it (binocular diplopia) or not (monocular, an optical problem).
- 05Saccades and pursuit: slowed saccades in a nerve palsy, an adducting eye that lags in an internuclear ophthalmoplegia.
- 06The rest of the third nerve: the lid and the pupil. The rest of the patient: the other cranial nerves, the fundus for papilloedema.
Double vision as the patient brings it: the diplopia pathway. The anatomy of the muscles on the 3D eye: anatomy lab.