Ophthalmic muscles and eye movements

Each eye has six oculomotor muscles attached, 4 primacy and 2 oblique.
They control the direction of our gaze and operate in cooperation
with the oculomotor muscles of the other eye. If for some reason the
muscles of the eyes do not work together harmoniously, the eyes
cannot focus simultaneously on the same spot, resulting in
strabismus.

The 4 primacy muscles sprout from deep within the orbit behind the
eyeball and end up in the sclera right before its change with the
cornea.

The action of the primacy muscles is equivalent to their location. Thus,
the medial rectus eye rotates inward (adduction), the lateral rectus
outwardly (abduction), the upward superior rectus (upper turning) and
the lower correct downwards (down shift). The two oblique muscles, in
contrast with the primacy muscles, overgrow behind the equator and
the oblique course makes their activity less obvious.

The upper oblique muscle originates from the depth of the orbit behind
the eyeball but travels forwardly passing through a cartilage
formation, located on the upper rim of the orbit and the nose, called
trochlea. The contraction of the upper oblique muscle leads to a down
shift of the eye, as well as the inner cyclic shift, i.e. rotation of
the eye around the sagittal axis, so that the 12th hour of the pivot
leans towards the nose.

The inferior oblique muscle does not originate from the depth of the
orbit, as the four primary and superior oblique muscles do, but as
the lacrimal bone, which is near the nose. The contraction leads to
upper shift and outer cyclic shift, i.e. rotation of the eye around
the sagittal axis, so that the 12th hour would evert (temporally).