×
Reference Material
Cranial Nerves of Extraocular Movement
| Nerve | Muscle(s) | Functions | Lesion Findings |
|---|---|---|---|
| Oculomotor (CN III) | Superior rectus, Medial rectus, Inferior rectus, Inferior oblique, Levator palpebrae superioris | Abduction, Depression, Elevation, External rotation | "Down and Out" gaze; Ptosis; Mydriasis; Loss of accommodation; Diagonal diplopia |
| Trochlear (CN IV) | Superior oblique | Abduction, Internal rotation, Depression while adducted | Eye deviated upward; Vertical & torsional diplopia |
| Abducens (CN VI) | Lateral rectus | Abduction | Eye deviated medially; Horizontal diplopia |
Diagrams (Click to Zoom)
Oculomotor Functions:
Palsy Findings:
High-Yield USMLE Study Tips
1. The "Formula" for Innervation
- LR6 SO4 (Lateral Rectus is CN VI; Superior Oblique is CN IV).
- Everything else is CN III.
2. Clinical "Pearls" for Lesions
- CN III Palsy: Parasympathetic fibers (pupil) are on the outside. Compression (aneurysm) hits pupil first (blown). Ischemia (diabetes) spares pupil.
- CN IV Palsy: Patients present with head tilt toward opposite side of lesion to compensate for lack of intorsion.
- CN VI Palsy: Often first sign of increased ICP due to long intracranial course.
3. Muscle Action Mnemonic
- Obliques go Opposite: Superior Oblique moves eye down, Inferior Oblique moves eye up.
- O's Abduct: Both Obliques contribute to Abduction.