Ocular motility defects occurring as a result of unilateral stereotactic thermal lesions in the midbrain pretectal areas have been observed in 16 patients. The preponderance of convergence defects leads to the conclusion that convergence function is not focally localized to the midline but is mediated more diffusely from pretectal regions of the midbrain. It appears as if midline structures are not the primary center for convergence. Miotic pupils in 15 patients suggests a diffuse association of accommodation and pupillary reaction which can be symmetrically affected by a unilateral lesion. The observation of skew deviation suggests that vertical gaze is also more diffusely organized in the dorsolateral midbrain. A unilateral stereotactic lesion can cause both bilateral paralysis of vertical gaze as well as skew deviation.
Nashold BS, Seaber JH. Defects of Ocular Motility After Stereotactic Midbrain Lesions in Man. Arch Ophthalmol. 1972;88(3):245-248. doi:10.1001/archopht.1972.01000030247003