Daniel R. Gold, DO, Departments of Neurology, Ophthalmology, Neurosurgery, Otolaryngology - Head & Neck Surgery, The Johns Hopkins School of Medicine
This is a 70-year-old woman who presented with diplopia at distance. Her exam demonstrated orthophoria at near with a fairly comitant 8-10 PD esotropia at distance without abduction paresis, consistent with divergence insufficiency (DI). With age, patients may develop an esodeviation greater at distance due to ‘sagging eye syndrome'. Sagging eye syndrome (referred to some as age-related distance esotropia) or age-related orbital involutional changes may cause divergence issues at distance due to LR-SR band rupture or distention causing the lateral rectus muscles to be at a mechanical disadvantage. A prominent superior sulcus and levator disinsertion with high lid creases are commonly seen as in this patient. Occasionally, DI is seen with cerebellar disease, and while this patient had features of sagging eye syndrome, she also had gaze-evoked and rebound nystagmus, and saccadic smooth pursuit, which can be seen in patients with cerebellar flocculus dysfunction. In rabbits, it has been shown that in rabbits, there exists an inhibitory projection from the cerebellar flocculus to the medial rectus (MR) subnuclei.1 Therefore, dysfunction of the flocculus could result in disinhibition of the MR and a convergence bias. This could provide an explanation for divergence insufficiency that is cerebellar in origin. Upon further questioning, she had experienced progressive imbalance over years, which was compatible with her irregular wide-based gait and consistent with cerebellar ataxia. MRI was unrevealing (no orbital sequences were available to evaluate the LR-SR band), and investigations for causes of reversible/treatable causes of cerebellar ataxia were negative. She responded very well to base out prism placed in her distance spectacles. 1.Ito M, Nisimaru N, Yamamoto M. Specific patterns of neuronal connexions involved in the control of the rabbit's vestibulo-ocular reflexes by the cerebellar flocculus. J Physiol 1977;265:833-854.
Spencer S. Eccles Health Sciences Library, University of Utah