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PURPOSE: To develop an algorithm in order to establish a consensus on how oculomotor nerve schwannomas should be treated by reviewing results from reported cases in the literature. Given the rarity of oculomotor nerve schwannomas, there is no agreed upon criteria for when a surgical or a nonsurgical intervention would be indicated. By reviewing former cases of oculomotor nerve schwannomas, our study proposes a flowchart for physicians to follow for optimal management. METHODS: The review of reported oculomotor nerve schwannoma cases involved 51 cases. From the 51 cases, data was tabulated including age, patient symptoms, symptom duration, tumor size, tumor location, treatment, post operative results, and follow up time. The cases were then divided in to surgical subgroup and a nonsurgical subgroup. Each case was also grouped based on post operative oculomotor function into improved, no change, and worsened groups. Our collaboration with Tufts Medical center also yielded 4 unreported cases of oculomotor nerve schwannoma that are described and compared to the previous 51 cases from the literature review. RESULTS: The review of the 51 reported cases yielded a few statistically significance differences between the surgical and nonsurgical subgroups. The surgical subgroup was older with a mean age of 35 years than the nonsurgical subgroup with a mean age of 15.8 years. The surgical group also had larger tumors with a mean tumor diameter of 29.5 mm versus the nonsurgical subgroup's 4.5 mm mean tumor diameter. The surgical subgroup also experienced shorter symptom durations as well. The mean duration of symptoms in the surgical subgroup was 17.8 months versus the 140 month mean symptom duration for the nonsurgical cases. Finally, the majority of surgically treated cases experienced a worsening of residual oculomotor function (20/38), while the majority of nonsurgically treated cases experienced little to no change in oculomotor function (11/13). CONCLUSION: Given the high likelihood of complete third nerve palsy after surgery, this study advocates a conservative approach to oculomotor nerve schwannomas that do not present with any life threatening symptoms or acutely deteriorating symptoms. The cases that are presented in this study also corroborate previous studies' findings on the efficacy of stereotactic radiosurgery in managing schwannoma size without resorting to more invasive interventions.

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Volitional target-selecting eye movements, such as saccades or smooth pursuit, are frequently considered distinct and separate from automatic gaze-stabilising eye movements like optokinetic nystagmus or the vestibulo-ocular reflex. This difference is regularly mapped onto brain anatomy, with distinctions made between subcortical, automatic processes; and cortical, volitional ones. However gaze-stabilising and target-selecting eye movements must work together when a moving observer views natural scenes. Yet such co-ordination would not be possible if automatic and volitional actions are sharply divided. This thesis focuses upon interactions between gaze-stabilising and target-selecting eye movements, and how these interactions can aid our understanding of the relationship between automatic and volitional processes. For a saccade executed during optokinetic nystagmus to accurately land on target, it must compensate for the ongoing optokinetic movement. It was found that targeting saccades can partially compensate for concomitant optokinetic nystagmus. The degree of compensation during optokinetic nystagmus was indistinguishable from compensation due to voluntary smooth pursuit displacements. A subsequent experiment found that locations are similarly misperceived during optokinetic nystagmus and smooth pursuit. Furthermore, saccade end-points are subject to the same perceptual mislocalisations. The next experiment established that fast-phases of optokinetic nystagmus can act like competitive saccades and cause curvature in targeting saccades. Moreover, optokinetic nystagmus fast-phases are delayed by irrelevant visual distractors in the same way as saccades (the saccadic inhibition effect). Lastly, it was established that the fast-phases of Infantile Nystagmus Syndrome also show the saccadic inhibition effect. In conclusion, target-selecting and gaze-stabilising eye movements show substantial co-ordination. Furthermore these results demonstrate considerable commonalties between ‘automatic’ and ‘volitional’ eye movements. Such commonalities provide further evidence there is no sharp distinction between automatic and volitional processes. Instead it is likely there are substantial interconnections between automatic and volitional mechanisms, and volition has a graded influence upon behaviour.

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