Vertical Eye Position Research Articles

Heidelberg Spectralis infrared video imaging: a clinical tool for diagnosing ocular torsional instability

Heidelberg Spectralis infrared video imaging provides a diagnostic modality for the assessment of dynamic torsional instability of the eyes. It accurately detects monocular changes in both vertical and torsional eye position as fixation is switched from one eye to the other without the need for illuminating either eye. Heidelberg Spectralis infrared video imaging is useful for depicting the subtle torsional components of dissociated vertical divergence, latent nystagmus in patients with infantile esotropia.

The Influence of Horizontal Convergence on Slow Oscillatory Eye Movements During Visual Fixation

Slow oscillatory eye movements (SOMs) occur simultaneously with tremor, drifts, and microsaccades during visual fixation. In a previous study, the amplitude of SOM was found to be affected by the visual characteristics of the stimuli. This indicates a perceptual influence on the control of the movement. However, the frequency of SOM did not change. The aim of our study was to investigate how SOM is affected by extraocular muscle tension. In a repeated-measurement experiment, 14 subjects were instructed to maintain fixation for 3 minutes on a bright dot presented at four distances (15, 30, 60, and 120 cm). The level of extraocular muscle tension is assumed to increase with decreased fixation distance due to convergence angle. Eye movements were recorded binocularly using a video eye tracker, and the amplitude and frequency of SOM for each eye were obtained by independently filtering the horizontal and vertical eye position signals with a discrete Fourier transformation. The results showed no significant differences for the amplitude. However, the horizontal frequency was found to be significantly lower at the closest distance. No significant differences were found for the vertical frequency. Based on these findings we conclude that extraocular muscle tension does have an effect on the frequency, but not the amplitude, of the oscillations. The apparent double dissociation between perceptual effects on amplitude versus muscle tension effects on frequency is discussed in relation to the origin and control of SOM.

Is Adaptation to Perceived Interocular Differences in Height Explained by Vertical Fusional Eye Movements?

To find out whether adaptation to a vertical prism involves more than fusional vertical eye movements. Adaptation to a vertical base-up 3 prism diopter prism was measured in a custom-programmed Maddox test in nine visually normal emmetropic subjects (mean age 27.0 ± 2.8 years). Vertical eye movements were binocularly measured in six of the subjects with a custom-programmed binocular video eye tracker. In the Maddox test, some subjects adjusted the perceived height as expected from the power of the prism while others appeared to ignore the prism. After 15 minutes of adaptation, the interocular difference in perceived height was reduced by on average 51% (from 0.86°-0.44°). The larger the initially perceived difference in height in a subject, the larger the amplitude of adaptation was. Eye tracking showed that the prism generated divergent vertical eye movements of 1.2° on average, which was less than expected from its power. Differences in eye elevation were maintained as long as the prism was in place. Small angles of lateral head tilt generated large interocular differences in eye elevation, much larger than the effects introduced by the prism. Vertical differences in retinal image height were compensated by vertical fusional eye movements but some subjects responded poorly to a vertical prism in both experiments; fusional eye movements were generally too small to realign both foveae with the fixation target; and the prism adaptation in the Maddox test was fully explained by the changes in vertical eye position, suggesting that no further adaptational mechanism may be involved.

A Quantitative Study of Fixation Stability in Amblyopia

To determine whether fixation instability contributes to reduced visual acuity in amblyopia, we compared fixation instability, quantified by the Nidek MP-1 microperimeter, in amblyopic and nonamblyopic children. Participants were 89 children (5-17 years old) with strabismus (n = 31), anisometropia (n = 29), or both conditions (n = 29). Fixation instability was measured using the Nidek MP-1 microperimeter, which calculated horizontal and vertical eye position at 25 Hz as the child attempted steady fixation for 30 seconds. Fixation instability was quantified as the 95% bivariate contour ellipse area (95% BCEA), the best-fit ellipse within which 95% of fixation occurred during the 30-second test. BCEA was normalized by log transformation. Children with amblyopia had significantly larger BCEAs for amblyopic eyes (mean = 0.56 log deg(2)) than fellow eyes (mean = 0.2 log deg(2), P < 0.01) and right eyes of normal controls (mean = 0.12 log deg(2), P ≤ 0.01). Fixation instability was significantly greater along the horizontal axis of the ellipse for amblyopic (mean = 3.53°) than fellow (mean = 1.98°, P = 0.008), and control (mean = 1.62°, P < 0.001) eyes. Fixation instability in amblyopic eyes of children with strabismus and/or anisometropia, and the associated poor stereoacuity probably is the consequence of decorrelated binocular experience early in life. Longer duration of decorrelated visual experience is associated with increased fixation instability, poorer stereoacuity, and more severe amblyopia. Treatments that minimize the duration of decorrelated visual experience may improve stereoacuity and decrease fixation instability.

Social Signals in Primate Orbitofrontal Cortex

Primate evolution produced an increased capacity to respond flexibly to varying social contexts as well as expansion of the prefrontal cortex. Despite this association, how prefrontal neurons respond to social information remains virtually unknown. People with damage to their orbitofrontal cortex (OFC) struggle to recognize facial expressions, make poor social judgments, and frequently make social faux pas. Here we test explicitly whether neurons in primate OFC signal social information and, if so, how such signals compare with responses to primary fluid rewards. We find that OFC neurons distinguish images that belong to socially defined categories, such as female perinea and faces, as well as the social dominance of those faces. These modulations signaled both how much monkeys valued these pictures and their interest in continuing to view them. Far more neurons signaled social category than signaled fluid value, despite the stronger impact of fluid reward on monkeys' choices. These findings indicate that OFC represents both the motivational value and attentional priority of other individuals, thus contributing to both the acquisition of information about others and subsequent social decisions. Our results betray a fundamental disconnect between preferences expressed through overt choice, which were primarily driven by the desire for more fluid, and preferential neuronal processing, which favored social computations.

Three-dimensional visuo-motor control of saccades

Although the motion of the line of sight is a straightforward consequence of a particular rotation of the eye, it is much trickier to predict the rotation underlying a particular motion of the line of sight in accordance with Listing's law. Helmholtz's notion of the direction-circle together with the notion of primary and secondary reference directions in visual space provide an elegant solution to this reverse engineering problem, which the brain is faced with whenever generating a saccade. To test whether these notions indeed apply for saccades, we analyzed three-dimensional eye movements recorded in four rhesus monkeys. We found that on average saccade trajectories closely matched with the associated direction-circles. Torsional, vertical, and horizontal eye position of saccades scattered around the position predicted by the associated direction-circles with standard deviations of 0.5°, 0.3°, and 0.4°, respectively. Comparison of saccade trajectories with the likewise predicted fixed-axis rotations yielded mean coefficients of determinations (±SD) of 0.72 (±0.26) for torsion, 0.97 (±0.10) for vertical, and 0.96 (±0.11) for horizontal eye position. Reverse engineering of three-dimensional saccadic rotations based on visual information suggests that motor control of saccades, compatible with Listing's law, not only uses information on the fixation directions at saccade onset and offset but also relies on the computation of secondary reference positions that vary from saccade to saccade.

Differential lateral rectus compartmental contraction during ocular counter-rolling.

The lateral rectus (LR) and medial rectus (MR) extraocular muscles (EOMs) have largely nonoverlapping superior and inferior innervation territories, suggesting functional compartmental specialization. We used magnetic resonance imaging (MRI) in humans to investigate differential compartmental activity in the rectus EOMs during head tilt, which evokes ocular counter-rolling, a torsional vestibulo-ocular reflex (VOR). MRI in quasi-coronal planes was analyzed during target-controlled central gaze in 90° right and left head tilts in 12 normal adults. Cross sections and posterior partial volumes of the transverse portions of the four rectus EOMs were compared in contiguous image planes 2 mm thick spanning the orbit from origins to globe equator, and used as indicators of contractility. Horizontal rectus EOMs had significantly greater posterior volumes and maximum cross sections in their inferior compartments (P < 10(-8)). In orbit tilt up (extorted) compared with orbit tilt down (intorted) head tilts, contractile changes in LR maximum cross section (P < 0.0001) and posterior partial volume (P < 0.05) were significantly greater in the inferior but not in the superior compartment. These changes were not explainable by horizontal or vertical eye position changes. A weaker compartmental effect was suggested for MR. The vertical rectus EOMs did not exhibit significant compartmental contractile changes during head tilt. Mechanical modeling suggests that differential LR contraction may contribute to physiological cyclovertical effects. Selective activation of the two LR, and possibly MR, compartments correlates with newly recognized segregation of intramuscular innervation into distinct compartments, and probably contributes to noncommutative torsion during the VOR.

Orbital Volume and Eye Position Changes After Balanced Orbital Decompression

To evaluate the changes in eye position and orbital content expansion following medial and lateral orbital wall decompression for thyroid-associated orbitopathy. The authors used a computer software program (syngo InSpace4D, syngo 3D, syngo fusion, and syngo Volume Evaluation; Siemens AG, Forchheim, Germany) to measure the orbital expansion gained by medial and lateral orbital wall decompression and the change in eye position between the digitized preoperative and postoperative orbital CT scans. Twenty patients (16 women and 4 men) with a mean age of 45 years (range, 18-64 years) were enrolled in this study. Of the 20 patients who underwent balanced decompression for thyroid-associated orbitopathy, 18 patients had bilateral medial and lateral orbital wall decompression, and 2 patients had unilateral medial and lateral decompression. The average orbital volume expansion was 3.21 mL (13.51%) of the preoperative orbital volume (2.1 mL [8.98%] gained by medial wall decompression and 1.03 mL [4.53%] by lateral wall decompression). Postoperatively, proptosis decreased by 2.53 mm on average (p < 0.0001). The eyes became closer to each other postoperatively in the horizontal plane by 2.6 mm on average (p < 0.0001). No change in the vertical eye position was detected postoperatively. A significant nasal shift in the eye position was noticed following balanced orbital decompression. Computerized assessment of preoperative and postoperative digitized orbital CT scans helps evaluate the orbital changes in response to different orbital decompression techniques and improve the surgical outcomes in thyroid-associated orbitopathy.

Eccentric gaze dynamics enhance vection in depth

This study examined the role of eccentric gaze dynamics in the generation of visual illusions of self-motion (i.e., vection). In Experiment 1, observers maintained their gaze either upward, downward, leftward, or rightward with respect to the center of a radially expanding optic flow pattern, which simulated forward self-motion in depth through a 3D cloud of objects. Real-time vection strength ratings and changes in horizontal and vertical eye positions were recorded simultaneously. Vection strength was found to increase progressively over the course of each 30-s presentation of radial flow. Eye tracking revealed strong optokinetic responses, consistent with ocular following responses (OFRs). Reported increases in vection strength in all four gaze conditions were typically preceded by reductions in slow-phase eye velocity. Similar results were found in Experiment 2, where displays simulated self-motion over a ground plane, which provided superior perspective. We conclude in both cases that enhancements of vection strength over time were temporally contingent upon the changing character of OFR while viewing these displays.

Context-specific saccadic adaptation in monkeys

When environmental or sensory conditions change suddenly, the brain must be capable of learning different behavioral modes to produce accurate movements under multiple circumstances. A form of this dual-state adaptation known as “context-specific adaptation” has been widely investigated using the saccade gain adaptation paradigm in humans. In this study, we asked whether or not context-specific adaptation of saccade gain exists in monkeys and if so to explore its properties. Here, vertical eye position was used as a context cue for adaptation of horizontal saccade gain. We asked for a gain-increase in one context and gain-decrease in another context, and then determined if a change in the context would invoke switching between the adapted states. After training, our monkeys developed context-specific adaptation: in most cases gain-decrease adaptation could be induced, but there was little or no gain-increase adaptation. This context-specific adaptation developed gradually and switching of gains was evident on the first saccades with each change in context. Along with these results, the retention of an adaptation aftereffect overnight indicates that contextual-specific adaptation in monkeys is not a strategy, but involves a true adaptive process of reorganization in the brain. We suggest that context-specific adaptation in monkeys could be an important tool to provide insights into the mechanisms of saccade adaptation that occurs during the more natural circumstances of daily life.

Visuomotor Velocity Transformations for Smooth Pursuit Eye Movements

Smooth pursuit eye movements are driven by retinal motion signals. These retinal motion signals are converted into motor commands that obey Listing's law (i.e., no accumulation of ocular torsion). The fact that smooth pursuit follows Listing's law is often taken as evidence that no explicit reference frame transformation between the retinal velocity input and the head-centered motor command is required. Such eye-position-dependent reference frame transformations between eye- and head-centered coordinates have been well-described for saccades to static targets. Here we suggest that such an eye (and head)-position-dependent reference frame transformation is also required for target motion (i.e., velocity) driving smooth pursuit eye movements. Therefore we tested smooth pursuit initiation under different three-dimensional eye positions and compared human performance to model simulations. We specifically tested if the ocular rotation axis changed with vertical eye position, if the misalignment of the spatial and retinal axes during oblique fixations was taken into account, and if ocular torsion (due to head roll) was compensated for. If no eye-position-dependent velocity transformation was used, the pursuit initiation should follow the retinal direction, independently of eye position; in contrast, a correct visuomotor velocity transformation would result in spatially correct pursuit initiation. Overall subjects accounted for all three components of the visuomotor velocity transformation, but we did observe differences in the compensatory gains between individual subjects. We concluded that the brain does perform a visuomotor velocity transformation but that this transformation was prone to noise and inaccuracies of the internal model.

Posterior parietal cortex areas MIP and LIPv receive eye position and velocity inputs via ascending preposito‐thalamo‐cortical pathways

Neuronal activity encoding eye position and gaze signals participates in updating the spatial representations found in the posterior parietal cortex and is necessary for spatial accuracy in goal-directed movements. Using retrograde transneuronal transfer of rabies virus in combination with a conventional tracer, we studied direct and polysynaptic inputs to the ventral lateral intraparietal area (LIPv) and medial intraparietal area (MIP) in non-human primates, to identify possible sources of eye position and gaze signals. We found that these areas receive disynaptic inputs from the brainstem horizontal eye position integrator network (nucleus prepositus hypoglossi, PH) via the central lateral and ventral lateral thalamic nuclei. Our findings provide the first demonstration that inputs from the horizontal eye position integrator reach cortical areas. We found important topographical differences between PH populations targeting MIP and LIPv that likely reflect transmission of different types of eye movement signals. LIPv receives projections from the ipsilateral rostral PH, which may transmit ipsilateral eye position signals. In addition to inputs from the rostral PH, MIP receives strong projections from the contralateral caudal PH, which may contribute to both eye position and velocity signals. Unlike the horizontal integrator, we found that the vertical eye position integrator network, the interstitial nucleus of Cajal, does not project to these posterior parietal areas, in keeping with findings that the thalamic nuclei targeting LIPv and MIP receive almost exclusively horizontal oculomotor signals.

Effect of Gravity on Vertical Eye Position

There is growing evidence that gravity markedly influences vertical eye position and movements. A new model for the organization of brainstem upgaze pathways is presented in this review. The crossing ventral tegmental tract (CVTT) could be the efferent tract of an "antigravitational" pathway terminating at the elevator muscle motoneurons in the third nerve nuclei and comprising, upstream, the superior vestibular nucleus and y-group, the flocculus, and the otoliths. This pathway functions in parallel to the medial longitudinal fasciculus pathways, which control vertical eye movements made to compensate for all vertical head movements and may also comprise the "gravitational" vestibular pathways, involved in the central reflection of the gravity effect. The CVTT could provide the upgaze system with the supplement of tonic activity required to counteract the gravity effect expressed in the gravitational pathway, being permanently modulated according to the static positions of the head (i.e., the instantaneous gravity vector) between a maximal activity in the upright position and a minimal activity in horizontal positions. Different types of arguments support this new model. The permanent influence of gravity on vertical eye position is strongly suggested by the vertical slow phases and nystagmus observed after rapid changes in hypo- or hypergravity. The chin-beating nystagmus, existing in normal subjects with their head in the upside-down position, suggests that gravity is not compensated for in the downgaze system. Upbeat nystagmus due to brainstem lesions, most likely affecting the CVTT circuitry, is improved when the head is in the horizontal position, suggesting that this circuitry is involved in the counteraction of gravity between the upright and horizontal positions of the head. In downbeat nystagmus due to floccular damage, in which a permanent hyperexcitation of the CVTT could exist, a marked influence of static positions of the head is also observed. Finally, the strongest argument supporting a marked role of gravity in vertical eye position is that the eye movement alterations observed in the main, typical physiological and pathological conditions are precisely those that would be expected from a direct effect of gravity on the eyeballs, with, moreover, no single alternative interpretation existing so far that could account for all these different types of findings.

Therapy of downbeat nystagmus: differential effects of aminopyridine on the gravity dependence and gaze – holding function

Aminopyridines (AP) have been shown to be an efficient therapy for downbeat nystagmus (DBN). Since AP improve both (i) resting discharge and (ii) excitability of floccular Purkinje cells (PC) we investigated the effect of AP on the vertical eye position sensitivity (EPS) and the gravity dependence (GD) in patients with idiopathic DBN. Eye movements towards targets presented in gaze straight ahead and±10° vertically were recorded prior to and 45 minutes after 20mg DAP or 4-AP ingestion in five pitch positions of the head relative to the upright position, i.e. from prone to supine head positions. Head position dependency of ocular drift was calculated from the difference between the lowest and highest SPV of the different head positions (GD=„gravity-dependence“).

Impact of Cognitive Task Complexity on Drivers’ Visual Tunneling

Cognitive distractions have been shown to affect drivers adversely and are a leading cause of accidents. Research indicates that drivers alter how they allocate their visual attention while engaging in secondary cognitive tasks. To evaluate the potential impact of secondary cognitive tasks on the allocation of drivers’ visual attention and on vehicle control, drivers were presented with increasingly complex forms of an auditory cognitive task while driving an instrumented vehicle. Measures of vehicle performance and eye gaze were assessed. Consistent with theories of visual tunneling, gaze distributions were significantly smaller while drivers performed certain levels of the secondary task; peripheral vision was thereby reduced. During the most difficult level of the secondary task, gaze dispersion was smaller than during any other level of the task. Changes in visual attention may provide earlier indications of cognitive distraction than changes in vehicle control, the latter of which were observed only during the most difficult level of the secondary task. Observed changes in vertical eye position suggest that drivers compensate for moderate cognitive demands by increasing their sight distance before further incremental increases in workload exceeded their abilities. In summary, the workload of a secondary cognitive task affected drivers’ visual attention. A low to moderate increase in workload was detectable as a change in gaze before vehicle control suffered. Gaze restriction appears related to the degree of cognitive workload. This work shows that visual attention is a potential method of detecting changes in driver state associated with cognitive workload.

Therapy of downbeat nystagmus: differential effects of aminopyridines on the gravity dependence and gaze holding function

Recently, aminopyridines (AP) have been shown to be an effective therapy for downbeat nystagmus (DBN). Since AP improve both (i) resting discharge and (ii) excitability of floccular Purkinje cells (PC), we investigated the effect of AP on the vertical eye position sensitivity (EPS) and the gravity dependence (GD) in a large group of patients with idiopathic DBN. We recorded vertical ocular drift velocity in gaze straight ahead and different vertical (±10°) and horizontal gaze positions in five pitch positions of the head between prone and supine (including upright) prior and 45 minutes after the ingestion of 3,4-diaminopyridine (DAP) or 4-AP.

Bone Vibration-Induced Nystagmus Is Useful in Diagnosing Superior Semicircular Canal Dehiscence

Objective: To explore vestibular integrity by bone vibration-induced nystagmus (VIN) during bedside examination. Disease or dysfunction of vestibular end organs would reduce or eliminate their contribution to total eye movement response to VIN. Background: It is assumed that vibration of the mastoid (at a frequency of 100 Hz) stimulates all vestibular end organs (semicircular canals and otolith structures). Previous studies have described oculomotor responses to vestibular activation by vibratory stimulus. Stimulation of individual semicircular canals produces eye movement in the plane of the stimulated canal. Vibratory stimulation of otolith structures (utricular macula) produces changes in ocular torsional position. Superior semicircular canal dehiscence (SCD) is responsible for nontypical cochleovestibular symptoms. Diagnosis is difficult without resorting to imaging, high-resolution computed tomography (HRCT) being the only tool providing reliable assessment. To avoid unnecessary referral for expensive imaging, it would be useful to have a simple screening test to select cases for HRCT. Methods: Video eye movements were recorded in complete darkness in patients diagnosed with SCD. The eye movement responses to long-lasting unilateral vibratory stimulation applied to the mastoid surface were evaluated. Results: VIN evoked a response in all cases, mostly demonstrating excitation of the affected side. The pattern of vertical, torsional and horizontal eye velocity and eye position was evaluated with three-dimensional infrared video-oculography (50 Hz sampling). Conclusion: Analysis of VIN, recently proposed to study transmission of excitatory stimuli by bone conduction, may be appropriate for altered immittance caused by dehiscence. This promises to be an interesting new field of research.

Initiation and Stability of Pursuit Eye Movements in Simulated Retinal Prosthesis at Different Implant Locations

To assess the possible effects of retinal prosthesis implant location on the initiation and stability of pursuit eye movements. Six normally sighted subjects visually tracked a horizontally moving target in natural vision and in simulated prosthetic vision. Subjects were instructed to press a key when the target jumped. Prosthetic vision was simulated with a 10 x 10 array of 1 degrees diameter phosphenes. Three implant locations in the retina were simulated: macular, 8 degrees superior, and 8 degrees nasal. Target motion had two speeds: 4 degrees /s and 8 degrees /s. Eye movement latency, horizontal stability, and vertical stability were assessed. Key-press behaviors responding to target jump were analyzed to evaluate functional eye movements. Compared with natural vision, horizontal eye position with respect to target position was less stable in simulated prosthetic vision at macular, superior, and nasal implant locations, in ascending order of the degree of instability. Vertical eye position with respect to target position in simulated prosthetic vision with the superior implant location was less stable in tracking slow target motion than fast. Eye movement latency in simulated prosthetic vision was longer than in natural vision. Key-press performance was impaired in simulated prosthetic vision. Pursuit eye movements in prosthetic vision, compared to natural vision, are significantly slower in initiation and less smooth in motion. They seem, however, still functional, even if the prosthesis is implanted in the peripheral retina. A superior implant locus may help the prosthesis wearer better control horizontal eye movements, which are more frequently used in the activities of daily living.

Adaptive neural mechanism for Listing's law revealed in patients with skew deviation caused by brainstem or cerebellar lesion.

Skew deviation is a vertical strabismus caused by damage to the otolithic-ocular reflex pathway and is associated with abnormal ocular torsion. This study was conducted to determine whether patients with skew deviation show the normal pattern of three-dimensional eye control called Listing's law, which specifies the eye's torsional angle as a function of its horizontal and vertical position. Ten patients with skew deviation caused by brain stem or cerebellar lesions and nine normal control subjects were studied. Patients with diplopia and neurologic symptoms less than 1 month in duration were designated as acute (n = 4) and those with longer duration were classified as chronic (n = 10). Serial recordings were made in the four patients with acute skew deviation. With the head immobile, subjects made saccades to a target that moved between straight ahead and eight eccentric positions, while wearing search coils. At each target position, fixation was maintained for 3 seconds before the next saccade. From the eye position data, the plane of best fit, referred to as Listing's plane, was fitted. Violations of Listing's law were quantified by computing the "thickness" of this plane, defined as the SD of the distances to the plane from the data points. Both the hypertropic and hypotropic eyes in patients with acute skew deviation violated Listing's and Donders' laws-that is, the eyes did not show one consistent angle of torsion in any given gaze direction, but rather an abnormally wide range of torsional angles. In contrast, each eye in patients with chronic skew deviation obeyed the laws. However, in chronic skew deviation, Listing's planes in both eyes had abnormal orientations. Patients with acute skew deviation violated Listing's law, whereas those with chronic skew deviation obeyed it, indicating that despite brain lesions, neural adaptation can restore Listing's law so that the neural linkage between horizontal, vertical, and torsional eye position remains intact. Violation of Listing's and Donders' laws during fixation arises primarily from torsional drifts, indicating that patients with acute skew deviation have unstable torsional gaze holding that is independent of their horizontal-vertical eye positions.

Eye orientation during static tilts and its relationship to spontaneous head pitch in the laboratory mouse

Both eye position and head orientation are influenced by the macular (otolith) organs, via the tilt maculo-ocular reflex (tiltMOR) and the vestibulo-collic reflexes, respectively. The mechanisms that control head position also influence the rest position of the eye because head orientation influences eye position through the tiltMOR. Despite the increasing popularity of mice for studies of vestibular and ocular motor functions, relatively little is known in this species about tiltMOR, spontaneous orientation of the head, and their interrelationship. We used 2D video oculography to determine in C57BL/6 mice the absolute horizontal and vertical positions of the eyes over body orientations spanning 360° about the pitch and roll axes. We also determined head pitch during ambulation in the same animals. Eye elevation varied approximately sinusoidally as functions of pitch or roll angle. Over the central ± 30° of pitch, sensitivity and gain in the light were 31.7°/ g and 0.53, respectively. The corresponding values for roll were 31.5°/ g and 0.52. Absolute positions adopted in light and darkness differed only slightly. During ambulation, mice carried the lambda–bregma plane at a downward pitch of 29°, corresponding to a horizontal eye position of 64° and a vertical eye position of 22°. The vertical position is near the center of the range of eye movements produced by the pitch tiltMOR. The results indicate that the tiltMOR is robust in this species and favor standardizing pitch orientation across laboratories. The robust tiltMOR also has significant methodological implications for the practice of pupil-tracking video oculography in this species.