Faculty Bibliography

Failure of brainstem supranuclear centers for saccadic eye movements results in the clinical presence of a brainstem-mediated supranuclear saccadic gaze palsy (SGP), which is manifested as slowing of saccades with or without range of motion limitation of eye movements and as loss of quick phases of optokinetic nystagmus. Limitation in the range of motion of eye movements is typically worse with saccades than with smooth pursuit and is overcome with vestibular-ocular reflexive eye movements. The differential diagnosis of SGPs is broad, although acute-onset SGP is most often from brainstem infarction and chronic vertical SGP is most commonly caused by the neurodegenerative condition progressive supranuclear palsy. In this review, we discuss the brainstem anatomy and physiology of the brainstem saccade-generating network; we discuss the clinical features of SGPs, with an emphasis on insights from quantitative ocular motor recordings; and we consider the broad differential diagnosis of SGPs.

The Savitzky-Golay (SG) filter is widely used to smooth and differentiate time series, especially biomedical data. However, time series that exhibit abrupt departures from their typical trends, such as sharp waves or steps, which are of physiological interest, tend to be oversmoothed by the SG filter. Hence, the SG filter tends to systematically underestimate physiological parameters in certain situations. This article proposes a generalization of the SG filter to more accurately track abrupt deviations in time series, leading to more accurate parameter estimates (e.g., peak velocity of saccadic eye movements). The proposed filtering methodology models a time series as the sum of two component time series: a low-frequency time series for which the conventional SG filter is well suited, and a second time series that exhibits instantaneous deviations (e.g., sharp waves, steps, or more generally, discontinuities in a higher order derivative). The generalized SG filter is then applied to the quantitative analysis of saccadic eye movements. It is demonstrated that (a) the conventional SG filter underestimates the peak velocity of saccades, especially those of small amplitude, and (b) the generalized SG filter estimates peak saccadic velocity more accurately than the conventional filter.

It is widely accepted that cerebral pathology can impair ocular motor and manual motor control. This is true in indolent and chronic processes, such as neurodegeneration and in acute processes such as stroke or those secondary to neurotrauma. More recently, it has been suggested that disruptions in these control systems are useful markers for prognostication and longitudinal monitoring. The utility of examining the relationship or the coupling between these systems has yet to be determined. We measured eye and hand-movement control in chronic, middle cerebral artery stroke, relative to healthy controls, in saccade-to-reach paradigms to assess eye-hand coordination. Primary saccades were initiated significantly earlier by stroke participants relative to control participants. However, despite these extremely early initial saccades to the target, reaches were nevertheless initiated at approximately the same time as those of control participants. Control participants minimized the time period between primary saccade onset and reach initiation, demonstrating temporal coupling between eye and hand. In about 90% of all trials, control participants produced no secondary, or corrective, saccades, instead maintaining fixation in the terminal position of the primary saccade until the end of the reach. In contrast, participants with stroke increased the time period between primary saccade onset and reach initiation. During this temporal decoupling, multiple saccades were produced in about 50% of the trials with stroke participants making between one and five additional saccades. Reaches made by participants with stroke were both longer in duration and less accurate. In addition to these increases in spatial reach errors, there were significant increases in saccade endpoint errors. Overall, the magnitude of the endpoint errors for reaches and saccades were correlated across participants. These findings suggest that in individuals with otherwise intact visual function, the spatial and temporal relationships between the eye and hand are disrupted poststroke, and may need to be specifically targeted during neurorehabilitation. Eye-hand coupling may be a useful biomarker in individuals with cerebral pathology in the setting of neurovascular, neurotraumatic, and neurodegenerative pathology.

Sensor fusion represents a robust approach to ecologically valid obstacle identification in building a comprehensive electronic travel aid (ETA) for the blind and visually impaired. A stereoscopic camera system and an infrared sensor with 16 independent elements is proposed to be combined with a multi-scale convolutional neural network for this fusion framework. While object detection and identification can be combined with depth information from a stereo camera system, our experiments demonstrate that depth information may be inconsistent given material surfaces of specific potential collision hazards. This inconsistency can be easily remedied by supplementation with a more reliable depth signal from an alternate sensing modality. The sensing redundancy in this multi-modal strategy, as deployed in this platform, may enhance the situational awareness of a visually impaired end user, permitting more efficient and safer obstacle negotiation.

Objective: To assess relationships between classic saccade sequences and rapid number naming on the King Devick (K-D) test in concussion. Background: The K-D test is sensitive for concussion detection on athletic sidelines, with longer test times in concussion largely due to inter-saccadic interval (ISI) prolongation. The ISI is a measure of time between saccades that represents a combination of fixation duration and saccade latency. K-D saccade latency cannot be directly measured, as numbers are simultaneously displayed. We assessed saccade latency independent of K-D test. Design/Methods: Twenty-seven chronically concussed participants (mean age 32+/-13 years, range 17-61) and 19 healthy controls (mean age 29+/-8 years, range 19-48) performed K-D and saccade sequences: reflexive, gap, overlap, and antisaccades. Eye movements were recorded with EyeLink 1000+ video-oculography. Results: K-D test times were longer in concussion (54.6s vs 41.5s, p=0.001), as were ISIs (301.9ms vs 241.4ms, p=0.01). Longer reflexive and overlap latencies (reflexive: 198.1ms vs 176.7ms, p=0.04; overlap: 222.3ms vs 182.8ms, p=0.003) and worse accuracy were seen in concussion. Gap latencies showed no difference (160.6ms vs 148.8ms, p=0.13). Antisaccade latencies were longer in concussion (204.9ms vs 182.3ms, p=0.04) for saccades initially made in the incorrect direction, though there was no difference in error rates. Peak velocity and duration versus amplitude relationships showed no differences between groups. Conclusions: ISI prolongation during K-D performance could be due to increased saccade latencies and/or attention and cognitive impairment. In this study, saccade latency prolongation is seen in several saccade types in concussion, suggesting that it may, indeed, contribute to K-D ISI prolongation in concussion. Further, overlap saccade latency prolongation suggests that pre-saccade visual fixation disengagement is altered in concussion. These results suggest that saccade motor planning is impaired in concussion, possibly from damage to frontal lobe saccade control centers prone to traumatic injury

Objective: The Mobile Universal Lexicon Evaluation System (MULES) is a new test of rapid picture naming that is under investigation in youth, collegiate and professional athlete cohorts as a concussion screening tool. The purpose of this study is to determine the ocular motor underpinnings, including saccade characteristics, required to perform this vision-based performance measure. Background: The MULES includes 54 color photographs of fruits, objects and animals. It has demonstrated excellent feasibility for administration among adult volunteers and in cohorts of athletes of all ages at pre-season baseline. MULES likely captures a more extensive vision network in the brain compared to rapid number naming, integrating saccades, color perception and object identification. Video-oculographic studies of the King-Devick (K-D) test of rapid number naming demonstrate prolonged inter-saccadic intervals (ISI) among individuals with longer testing times. Design/Methods: Participants underwent testing with the paper-based MULES as well as the computer screen-based version (eMULES) designed for simultaneous testing with infrared-based video-oculography (Eye Link 1000+). Saccade velocity, duration and the inter-saccadic interval were measured. Results: Among adult volunteers (n=23, aged 19-45) and patients with recent concussion (n=6, aged 17-43), those with the greatest number of saccades had the longest eMULES completion times ( f0 . 48 , p=0.008). In this cohort, prolonged ISI was not associated with greater eMULES testing times (AS=0.06, p=0.76). Conclusions: Longer testing times for the MULES likely reflect greater numbers of saccades rather than prolongation of the ISI. This pattern may reflect greater degrees of cognitive activity and visual pathway complexity for picture compared to number naming. Underlying dynamics for eye movements are likely to differ between the MULES and K-D, supporting complementary roles for each in concussion assessment

Objective: To compare video-oculography performed by EyeTribe versus EyeLink during a rapid number naming task. Background: With increasing accessibility of portable, economical, video-based, infrared eye trackers, such as EyeTribe, there is growing interest in eye movement recordings, including in the setting of sports-related concussion. However, prior to implementation, there is a primary need to establish the validity of these low-resolution (30-60 Hz) eye trackers via comparison with high-resolution (500-1000 Hz) devices such as EyeLink. Design/Methods: A convenience sample of 30 controls performed a digitized version of the King-Devick (K-D) test with EyeTribe and EyeLink eye movement recordings. Results: Signal loss and tracings inconsistent with eye movement physiology were common with EyeTribe. Saccade main sequence parameters (fit to decaying exponentials) were significantly different for the two devices (reported as best-fit parameter and 95% confidence interval). Peak velocity versus amplitude relationships revealed a main sequence asymptote of 1674degree/s (CI: 1527, 1852degree/s) for EyeTribe vs. 506degree/s (CI: 499, 513degree/s) for EyeLink and a time constant of 102.9degree (CI: 93.5,115.7degree) for EyeTribe vs. 6.1degree (CI: 5.3, 6.3degree) for EyeLink. Duration versus amplitude relationships also demonstrated significant differences, with an asymptote of 62.7ms (CI: 61.0, 64.3ms) for EyeTribe vs. 83.2ms (CI: 82.2, 84.4ms) for EyeLink and time constant of 4.9degree (CI: 4.6, 5.3degree) for EyeTribe vs. 13.8degree (CI: 13.6, 14.1degree) for EyeLink. Total number of saccades to complete the K-D was significantly lower with EyeTribe, with an average of 110.2 vs. 120.5 saccades recorded by EyeTribe and EyeLink respectively (paired t-test, p=0.001). There was no significant difference in the inter-saccadic interval, despite a discrepancy of 42ms between devices. Conclusions: The EyeTribe device was unable to capture valid saccade data during rapid number naming. Caution is advised regarding the implementation of eye trackers with low temporal resolution for objective saccade assessment or sideline concussion screening

Objective: To describe a case of gaze-position dependent opsoclonus and discuss potential localization. Background: Opsoclonus is characterized by bursts of involuntary, back-to-back saccades without an intersaccadic interval at frequency of 10-25 Hz in horizontal, vertical, and torsional planes. Opsoclonus with gaze-directional selectivity has been rarely described. Design/Methods: We report a 50 year-old man who sustained a concussion three years prior followed by postconcussive headaches and disequilibrium. Exam revealed very small amplitude oscillations in left gaze that could not be further characterized on clinical exam. Different larger amplitude horizontal oscillations were present with convergence. There were no other posterior fossa signs. Brain MRI was unremarkable. Results: Video-oculography demonstrated opsoclonus predominantly in left gaze [median amplitude 5 deg (range <1- 11 deg), frequency 30 Hz] and during leftward smooth pursuit, which improved [median amplitude 2 deg (range < 1-10 deg), frequency 10 Hz] as post-concussive symptoms improved. Conclusions: This case demonstrates opsoclonus with eye position selectivity in post-concussive syndrome. Various theories of opsoclonus exist, including lesions of saccade burst, omnipause, or cerebellar fastigial pause neurons which project to brainstem burst neurons. Ultimately, all of these lead to increased excitability in the inherently unstable saccade generators. Burst and omnipause neuron firing rates are not influenced by eye position. The leftward gaze-dependence in our case supports dysfunction of cerebellar dorsal vermis Purkinje cells leading to disinhibition of the fastigial ocular motor nucleus, as vermal pause neurons have gaze-directional selectivity. Vermal pause neurons exhibit a pause of discharge immediately before and during contralateral saccades. Thus, selective dysfunction, possibly related to concussion-related membrane instability, could create an imbalance in burst neuron excitability, resulting in triggering of unidirectional opsoclonus. Further, our patient's saccade system may be inherently prone to oscillations given the presence of larger amplitude horizontal oscillations consistent with 'voluntary flutter', which persisted when leftward opsoclonus improved