Functional topography as a guideline for differential diagnosis of vertical eye movement disorders and oblique muscle surgery

Aims: The differential diagnosis of congenital superior oblique paresis (strabismus sursoadductorius), acquired superior oblique paresis and inferior oblique overaction are discussed. In this study the purpose of the graphic description of a lever arm, "equal-line", crossing points of equal lines, "functional pole", in primary position (functional topography), are described. The efficacy of functional and mechanical guidelines for oblique muscle surgery are discussed. Patients and methods: The pattern of motility disorders (clinical measurements of three patients), congenital oblique paresis (strabismus sursoadductorius SSA), aquired superior oblique paresis (SOP) and inferior oblique overaction (IOO) are compared with the mechanical situation (functional topography) of eye-motility. Results: In a mechanical eye model SSA can be created as a concomitant vertical pattern of movement disorder with excyclorotation by a sagittalisation of the functional inferior oblique muscle origin (pulley-displacement). SOP with normal functional origin and insertion of superior and inferior oblique muscle can be created only by weakening (less muscle strength) the superior oblique muscle. IOO is constructed by a sagittalisation of muscle insertion of inferior oblique muscle and desagittalisation of insertion of superior oblique muscle. An ideal insertion line of the oblique muscles can be created at the surface of the eyeball by connecting points of the same main function. There are crossing points (areas) of this equal line projected at the "functional pole" at different gaze positions. At this equal-line the oblique muscle has to be fixed in recession or reforcing surgery to get a normal eye function. Conclusion: The findings of Bielschowskys' strabismus sursoadductorius as a vertical motility disorder with its own typical clinical appearance as well as SOP and IOO are confirmed by the clinical and vectorial results. In oblique muscle surgery a functional topography helps to prevent errors in eye muscle surgery.