Abstract
The superior oblique (SO) insertion is the most variable of the extraocular muscles, which, combined with its unusual anatomy, makes surgery difficult and unpredictable. This study aims to improve the ability of surgeons to identify and operate successfully on the SO, by characterising the variability in the size, position, angle and shape of its insertion. A secondary aim was to define clinical guidelines for steroid injections into the trochlear area to treat SO pathology.
Dissection was performed on eight paired cadaveric orbits, with measurements taken relating to the morphometry of the SO muscle and its insertional pattern onto the globe. Scale diagrams of its insertion were constructed based on these measurements. The medial canthus is attached to bone suggesting it may provide a good surface landmark for trochlear injection. To test this hypothesis, multiple trochlear injections were performed in each specimen and the position of the injection site relative to the medial canthus was measured.
Accessory SO insertions were present in both eyes from one donor. Although multiple insertions are common for the inferior oblique muscle, this has not previously been reported for the SO. It was found that the medial canthus provides a good landmark for how far laterally (but not superiorly) to inject.
Identifying variation in the SO insertion and useful landmarks may provide a roadmap for easier, safer SO surgery.
Guidelines for clinicians on how to find and manipulate the SO in clinical practice have been developed.