Saccadic intrusions in amyotrophic lateral sclerosis (ALS)

The attempt to quietly fixate at a small visual object is continuously interrupted by a variety of fixational eye movements comprising, among others, a continuum of saccadic intrusions (SI) which range in size from microsaccades with amplitudes ≤0.25° to larger refixation saccades of up to about 2°. The size and frequency of SI varies considerably among individuals and is known to increase in neurodegenerative diseases such as progressive supranuclear palsy (PSP), and amyotrophic lateral sclerosis (ALS). However, studies of ALS disagree whether also the frequency of SI increases. We undertook an analysis of SI in 119 ALS patients and 47 age-matched healthy controls whose eye movements during fixation and tests of executive functions (e.g antisaccades) had been recorded by video-oculography according to standardised procedures. SI were categorised according to their spatio-temporal patterns as stair case, back-and-forth and square wave jerks (a subcategory of back-and-forth). The SI of patients and controls were qualitatively similar (same direction preferences, similar differences between patterns), but were enlarged in ALS. Notably however, no increase of SI frequency could be demonstrated. Yet, there were clear correlations with parameters such as eye blink rate or errors in a delayed saccade task that suggest an impairment of inhibitory mechanisms, in keeping with the notion of a frontal dysfunction in ALS. However, it remains unclear how the impairment of inhibitory mechanisms in ALS could selectively increase the amplitude of intrusions without changing their frequency of occurrence.

Spontaneous eye blink rate as predictor of dopamine-related cognitive function-A review

An extensive body of research suggests the spontaneous eye blink rate (EBR) is a non-invasive indirect marker of central dopamine (DA) function, with higher EBR predicting higher DA function. In the present review we provide a comprehensive overview of this literature. We broadly divide the available research in studies that aim to disentangle the dopaminergic underpinnings of EBR, investigate its utility in diagnosis of DA-related disorders and responsivity to drug treatment, and, lastly, investigate EBR as predictor of individual differences in DA-related cognitive performance. We conclude (i) EBR can reflect both DA receptor subtype D1 and D2 activity, although baseline EBR might be most strongly related to the latter, (ii) EBR can predict hypo- and hyperdopaminergic activity as well as normalization of this activity following treatment, and (iii) EBR can reliably predict individual differences in performance on many cognitive tasks, in particular those related to reward-driven behavior and cognitive flexibility. In sum, this review establishes EBR as a useful predictor of DA in a wide variety of contexts.

SmartEye: Developing a Novel Eye Tracking System for Quantitative Assessment of Oculomotor Abnormalities

Eye movements are a continuous and ubiquitous part of sensory perception. To properly generate highly accurate and co-ordinate ocular movements, a vast network of brain areas are engaged, from low-level visual processing to motor control of gaze orientation. This renders oculomotor system vulnerable to various neurological disorders with unique clinical patterns. Therefore, oculomotor examination can serve as an early and sensitive indicator for various neurological conditions. A simple-to-use, clinically valid system for objectively assessing the oculomotor function can thus bring a paradigm shift in diagnosis and treatment of brain disorders. In principal accordance, this paper presents a gaze assessment tool, called SmartEye, which is based on eye fixation, smooth pursuit, and blinking in response to both static and dynamic visual stimuli. The gaze related indices were evaluated in real-time by SmartEye and these were mapped to the reported pathological state in chronic ( > 3 months) patients with stroke. Our preliminary feasibility study with eight pairs of chronic ( > 3 months) stroke survivors and healthy individuals revealed that gaze related indices in response to both static and dynamic visual stimuli may serve as potential quantitative biomarkers for stroke assessment.