• The orbit forms a pyramid in which the lateral and medial walls are at 45* to each other, and the central
axis is thus at 22.5* (approximated to 23*).
• The superior oblique (SO; like the levator palpebrae superioris) originates from the orbital apex outside
the annulus; in contrast, the inferior oblique (IO) arises from the nasal orbital fl oor.
• The obliques lie inferior to their corresponding rectus (R) muscle (i.e., SO lies inferior to SR and IO
inferior to IR).
• The spiral of Tillaux describes the way the recti insert increasingly posterior to the limbus (MR, IR, LR,
• Innervation is by CN III for SR, MR, IR, IO; by CN IV for SO; and by CN VI for LR.
4. Superior view of the right globe showing muscle
insertions (LPS removed).
Lateral view of the right globe showing
muscle insertions (LR partly removed).
5. PHYSIOLOGY (EYE MOVEMENTS)
• Eye movements may be monocular (ductions) or binocular (versions and vergences).
• Versions are conjugate eye movements, i.e., both eyes move in the same direction, whereas vergences
are disconjugate, i.e., both eyes move in opposite directions.
• Eye movements may be described as rotations of the globe around horizontal (x), anteroposterior (y),
and vertical (z) axes—the axes of Fick.
7. • The extraocular muscles do not act in isolation.
• Each agonist (e.g., LR) has an antagonist that acts in the opposite direction in the same eye (i.e.,
• Increased innervation of the agonist is accompanied by decreased innervation of its antagonist
• Each agonist also has a yoke muscle that acts in the same direction in the other eye (i.e., contralateral
MR in this example).
• During conjugate movement yoke muscles receive equal and simultaneous innervation (Hering’s law).