Abstract

Successful surgery on the inferior oblique (IO) relies on detailed knowledge of its insertional pattern and proximity to adjacent structures. This study investigates variability in IO anatomy, develops heuristics to assist in surgical technique selection and tests the hypothesis that the two oblique muscles lie within a shared muscular plane.

Dissection of 8 paired cadaveric orbit specimens were completed to expose the IO muscle along its course. The angle of the IO was measured relative to the visual axis from both lateral and inferior views. Measurements of the angle of the superior oblique (SO) muscle tendon to the visual axis, the morphometry of the muscle, nerve and insertional pattern were also completed.

Significant differences between IO and SO angles (p=0.0093) disproved the null hypothesis of a common plane. Using measurements of the insertional location, diagrams were constructed to create an intuitive scale-accurate visual map to help guide strabismus surgeons. These were paired with trace diagrams to show the variability in insertion shape. The inferior temporal vortex vein was found to have a relatively constant location as a key landmark for IO muscle capture during surgery.

Detailed knowledge of insertional variability and proximity to the optic nerve and ciliary arteries should improve surgeon confidence in identifying and manipulating the IO. IO angle measurements can be used to improve eye movement and surgical training models.

This paper should improve surgical outcomes by providing a detailed insertional map of the IO, while simultaneously challenging long-held assumptions of the obliques’ muscular plane.