The body of the superior oblique muscle is located " behind " the eyeball, but the tendon ( which is redirected by the trochlea ) approaches the eyeball from the " front ".
32.
This is because as the eye is abducted ( looks laterally ), the contribution made by superior oblique to depression of the eye decreases, as the inferior rectus muscle causes this movement more directly and powerfully.
33.
While at Leipzig he worked under physiologist Ewald Hering ( 1834-1918 ), and with Franz Bruno Hofmann ( 1869-1926 ), he conducted studies of fusion and cyclodeviation in superior oblique muscle paresis.
34.
The main muscle for abduction is the lateral rectus, so although superior oblique contributes to a downwards and lateral eye movement, testing this motion would not be specific enough as inferior and lateral recti muscles would also be tested.
35.
For example, the tendon of the superior oblique inserts " behind " the equator of the eyeball in the frontal plane, so contraction of the muscle also tends to " abduct " the eyeball ( turn it outward ).
36.
In order to understand the actions of the superior oblique muscle, it is useful to imagine the eyeball as a sphere that is constrained like the trackball of a computer mouse in such a way that only certain rotational movements are possible.
37.
To summarize, the actions of the superior oblique muscle are ( 1 ) " depression " of the eyeball, especially when the eye is adducted; and ( 2 ) " intorsion " of the eyeball, especially when the eye is abducted.
38.
The sixth nerve, the abducens nerve, which innervates the lateral rectus muscle of the eye ( moves the eye laterally ), is also commonly affected but fourth nerve, the trochlear nerve, ( innervates the superior oblique muscle, which moves the eye downward ) involvement is unusual.
39.
The superior oblique muscle ends in a tendon that passes through a fibrous loop, the "'trochlea "', located anteriorly on the medial aspect of the orbit . " Trochlea " means pulley in Latin; the fourth nerve is named after this structure.
40.
Trochleitis is diagnosed based on three criteria : 1 ) demonstration of inflammation of superior oblique tendon / trochlea region, 2 ) periorbital pain and tenderness to palpation in the area of the sore trochlea, and 3 ) worsening of pain on attempted vertical eye movement, particularly with adduction of the eye.