Prior studies of the human translational vestibulo-ocular reflex (tVOR) report that eye rotations amount to less than 60% of those required to keep the eyes pointed at a stationary visual target, unlike the angular VOR (aVOR) which is optimized to maintain stable gaze. Our first goal was to determine if the performance of the tVOR improves when head translations are combined with head rotations in ambient lighting. A second goal was to measure tVOR during vertical head translations (bob), which has not received systematic study. We measured tVOR alone and in combination with the aVOR in 20 normal human subjects, aged 25-72 years, as they sat on a moving platform that bobbed at 2.0 Hz while rotating horizontally (yaw) at 1.0 Hz. When subjects viewed a visual target at 2 m, median "compensation gain" (eye rotational velocity/required eye rotational velocity to maintain foveal target fixation) was 0.52 during pure bob and 0.59 during combined bob-yaw; during viewing of a near target at approximately 17 cm, compensation gain was 0.58 for pure bob and 0.60 for combined bob-yaw. Mean phase lag of eye-in-head velocity for the tVOR was approximately 19 degrees with respect to the ideal compensatory response, irrespective of whether translation was accompanied by rotation. Thus, the tVOR changed only slightly during translation-rotation versus pure translation, and our subjects' ocular rotations remained at about 60% of those required to point the eyes at the target. Comparison of response during binocular or monocular viewing, and ambient or reduced illumination, indicated that relative image motion between the target and background was an important determinant of tVOR behavior. We postulate that tVOR evolved not to stabilize the image of the target on the fovea, but rather to minimize retinal image motion between objects lying in different planes, in order to optimize motion parallax information.

Progressive supranuclear palsy (PSP) is a disease of later life that is currently regarded as a form of neurodegenerative tauopathy. Disturbance of gaze is a cardinal clinical feature of PSP that often helps clinicians to establish the diagnosis. Since the neurobiology of gaze control is now well understood, it is possible to use eye movements as investigational tools to understand aspects of the pathogenesis of PSP. In this review, we summarize each disorder of gaze control that occurs in PSP, drawing on our studies of 50 patients, and on reports from other laboratories that have measured the disturbances of eye movements. When these gaze disorders are approached by considering each functional class of eye movements and its neurobiological basis, a distinct pattern of eye movement deficits emerges that provides insight into the pathogenesis of PSP. Although some aspects of all forms of eye movements are affected in PSP, the predominant defects concern vertical saccades (slow and hypometric, both up and down), impaired vergence, and inability to modulate the linear vestibulo-ocular reflex appropriately for viewing distance. These vertical and vergence eye movements habitually work in concert to enable visuomotor skills that are important during locomotion with the hands free. Taken with the prominent early feature of falls, these findings suggest that PSP tauopathy impairs a recently evolved neural system concerned with bipedal locomotion in an erect posture and frequent gaze shifts between the distant environment and proximate hands. This approach provides a conceptual framework that can be used to address the nosological challenge posed by overlapping clinical and neuropathological features of neurodegenerative tauopathies.

We conducted a masked, cross-over, therapeutic trial of gabapentin (1200mg/day) versus memantine (40mg/day) for acquired nystagmus in 10 patients (28-61 years; 7 female; MS: 3, poststroke: 6, post-traumatic: 1). Nystagmus was pendular in 6 patients (oculopalatal tremor: 4, MS: 2) and jerk upbeat, hemi-seesaw, torsional, or upbeat-diagonal in each of the others. Both drugs reduced median eye speed (p<0.001), gabapentin by 32.8% and memantine by 27.8%, and improved visual acuity (p<0.05). Each patient improved with one or both drugs. Side-effects included unsteadiness with gabapentin and lethargy with memantine. Both drugs should be considered as treatment for acquired forms of nystagmus.

These data suggest that, in animals with sensory-induced strabismus, central innervation to extraocular muscles is responsible for setting the state of strabismus. Mechanical factors such as muscle length adaptation (for horizontal misalignment) and pulley heterotopy or static torsion (for "A" patterns) likely do not play a major role in determining properties in a sensory-induced strabismus.

Taken together, these results indicate that abnormal otolith-mediated reflexes may be at least partly responsible for frequent falls in progressive supranuclear palsy, and deserve further study.