Search Results (13)

Age-related cognitive impairment represents a critical stage in the continuum of neurodegenerative disorders, including Alzheimer’s disease (AD), highlighting the need for objective and non-invasive physiological indicators of early neurological change. This study investigates the simultaneous analysis of microsaccadic eye movements and pupil size variations as ocular biomarkers associated with age-related cognitive impairment using eye-tracking technology. A total of 70 participants were recruited and categorized into three age groups: individuals in their 20s, 60s, and 70s. Participants in their 70s were further categorized based on MMSE-K scores into cognitively normal (≥24) and impaired (≤23) subgroups. Quantitative analyses showed a significant age-related increase in microsaccade frequency along both axes, with significantly higher microsaccade frequencies (p < 0.01) among individuals with lower cognitive scores within the same age group. Pupil size variation, including constriction and dilation rates, declined with age, while response speed remained relatively unchanged across all age groups. These findings highlight a clear association between age related-cognitive decline and involuntary ocular responses. The proposed dual-biomarker method offers a non-invasive and quantitative framework that may complement traditional cognitive screening tools. Future studies involving larger cohorts and clinically diagnosed AD populations are required to determine the diagnostic utility of these ocular biomarkers. Full article

Non-human primates (NHPs) are extensively utilized to investigate the neural mechanisms underlying face processing; however, measuring their brain activity necessitates a diverse array of technologies. Pupillometry emerges as a convenient, cost-effective, and non-invasive alternative for indirectly assessing brain activity. To evaluate the efficacy of pupillometry in assessing facial and emotional processing in NHPs, this study designed a face fixation task for experimental monkeys (Rhesus macaque) and recorded variations in their pupil size in response to face images with differing characteristics, such as species, emotional expression, viewing angles, and orientation (upright vs. inverted). All face images were balanced with luminance and spatial frequency. A sophisticated eye-tracking system (Eye-link 1000 plus) was employed to observe the pupils and track the viewing trajectories of monkeys as they examined images of faces. Our findings reveal that monkeys exhibited larger pupil sizes in response to carnivore faces (versus human faces, p = 0.035), negative conspecific faces (versus human faces, p = 0.018), and profile viewing angles (versus frontal view angles, p = 0.010). Notably, pupil size recorded during the 500–1000 ms post-stimulus interval was negatively correlated with their gaze durations directed at those images (r = −0.357, p = 0.016). Overall, this study demonstrates that pupillometry effectively captures subtle differences in facial and emotional processing, underscoring its potential as a valuable tool in future cognitive research and the diagnosis of disorders. Full article

The impact of ambient brightness surroundings on the peak velocities of visually guided saccades remains a topic of debate in the field of eye-tracking research. While some studies suggest that saccades in darkness are slower than in light, others question this finding, citing inconsistencies influenced by factors such as pupil deformation during saccades, gaze position, or the measurement technique itself. To investigate these, we developed RELAY (Robotic EyeLink AnalYsis), a low-cost, stepper motor-driven artificial eye capable of simulating human saccades with controlled pupil, gaze directions, and brightness. Using the EyeLink 1000, a widely employed eye tracker, we assessed accuracy and precision across three illumination settings. Our results confirm the reliability of the EyeLink 1000, demonstrating no artifacts in pupil-based eye tracking related to brightness variations. This suggests that previously observed changes in peak velocities with varying brightness are likely due to human factors, warranting further investigation. However, we observed systematic deviations in measured pupil size depending on gaze direction. These findings emphasize the importance of reporting illumination conditions and gaze parameters in eye-tracking experiments to ensure data consistency and comparability. Our novel artificial eye provides a robust and reproducible platform for evaluating eye tracking systems and deepening our understanding of the human visual system. Full article

Background: Handheld quantitative pupilometers (QPs) measure each phase of the pupillary light reflex (PLR) and provide a summary score based on these values. One phase of the PLR is the period of time from the onset of light exposure to the maximum constriction of the pupil, also known as time to maximum constriction (tMC). Although tMC has been found to vary significantly among patients with neurological injury, there are no studies reporting tMC in healthy controls. This study addresses this gap. Methods: Subjects in this prospective observational study were healthy controls who provided paired (left and right eye) QP readings during four separate observations over the course of 2 days. The tMC was derived by determining the smallest observed pupil size during videos filmed at 30 frames per second, and we assessed within-subject variability using the coefficient of variance and intraclass correlation coefficient (ICC). Results: Fifty subjects provided 380 QP readings (190 left eye and 190 right eye). Subjects primarily identified as female (80%), non-Hispanic (86%), white (62%), and <40 years old (74%). The mean tMC was 1.0 (0.14) seconds (s) for the left eye and 1.0 (0.17) s for the right eye; the coefficient of variance ranged from 11.6% to 18.8% and the ICC ranged from 0.25 to 0.40. For the between-subject comparisons across the four observation periods, the left and right eye mean differences ranged from 0.001 to 0.063 and the ICC ranged from 0.12 to 0.52. Conclusions: The tMC values vary significantly in healthy controls. Changes in pupil function as a clinical biomarker of intracranial pathology are not fully understood. Identifying clinical correlations of tMC variation may provide insight for the prognostication and treatment of neurocritically ill patients. Full article

Purpose: To assess the possible impact of minor changes in fixation on wavefront measurements as a potential constraint in detecting subtle temporal variations in ocular wavefront error. Methods: Twelve healthy subjects with an average age of 36.3 ± 8.8 were instructed to put their heads in the aberrometer’s chin-rest and look at a fixation target that was embedded in the device. The fixation targets were readily observable to the participants without accommodation, thanks to the aberrometer’s Badal system. When each eye was staring at the target, its wavefront aberration was recorded three times and then averaged for further analysis. The averaged Zernike coefficients were rescaled to the smallest value of the maximum round pupil found among all eyes (4.41 mm), and this procedure was repeated for each target. Results: Alteration of the fixation targets caused changes to the Zernike coefficients of defocus (C(2,0)), vertical trefoil (C(3,–3)), vertical coma (C(3,–1)), horizontal coma (C(3,1)), oblique trefoil (C(3,3)), primary spherical aberration (C(4,0)), and secondary spherical aberration (C(6,0)), but the changes were not statistically significant. Nevertheless, an alteration in the target’s size and shape exhibited a significant correlation across all of the aforementioned coefficients in both eyes (p < 0.05). The total RMS of aberrations and the RMS of the spherical-like aberrations were both lowest while choosing the larger Maltese cross, and the bigger E-letter minimized the RMS of HOA and comatic aberrations. Conclusion: The aberrometric changes occur as a consequence of altering the fixational gaze and are within the range of the changes found after performing a near-vision task, so they might potentially act as a confounding factor when attempting to identify such small variations in the ocular wavefront. Using a smaller E-letter (5 arcmin) as an internal fixation target resulted in the least standard deviation of measurements, fixational stability, and higher accuracy in ocular wavefront measurements. Full article

Training in healthcare skills can be affected by trainees’ workload when completing a task. Due to cognitive processing demands being negatively correlated to clinical performance, assessing mental workload through objective measures is crucial. This study aimed to investigate task-evoked changes in pupil size as reliable markers of mental workload and clinical performance. A sample of 49 nursing students participated in a cardiac arrest simulation-based practice. Measurements of cognitive demands (NASA-Task Load Index), physiological parameters (blood pressure, oxygen saturation, and heart rate), and pupil responses (minimum, maximum, and difference diameters) throughout revealed statistically significant differences according to performance scores. The analysis of a multiple regression model produced a statistically significant pattern between pupil diameter differences and heart rate, systolic blood pressure, workload, and performance (R² = 0.280; F (6, 41) = 2.660; p < 0.028; d = 2.042). Findings suggest that pupil variations are promising markers to complement physiological metrics for predicting mental workload and clinical performance in medical practice. Full article

Emotion detection is a fundamental component in the field of Affective Computing. Proper recognition of emotions can be useful in improving the interaction between humans and machines, for instance, with regard to designing effective user interfaces. This study aims to understand the relationship between emotion and pupil dilation. The Tobii Pro X3-120 eye tracker was used to collect pupillary responses from 30 participants exposed to content designed to evoke specific emotions. Six different video scenarios were selected and presented to participants, whose pupillary responses were measured while watching the material. In total, 16 data features (8 features per eye) were extracted from the pupillary response distribution during content exposure. Through logistical regression, a maximum of 76% classification accuracy was obtained through the measurement of pupillary response in predicting emotions classified as fear, anger, or surprise. Further research is required to precisely calculate pupil size variations in relation to emotionally evocative input in affective computing applications. Full article

Saccadic eye movements are directed to the objects of interests and enable high-resolution visual images in the exploration of the visual world. There is a trial-to-trial variation in saccade dynamics even in a simple task, possibly attributed to arousal fluctuations. Previous studies have showed that an increase of fatigue level over time, also known as time-on-task, can be revealed by saccade peak velocity. In addition, pupil size, controlled by the autonomic nervous system, has long been used as an arousal index. However, limited research has been done with regards to the relation between pupil size and saccade behavior in the context of trial-to-trial variation. To investigate fatigue and arousal effects on saccadic and pupillary responses, we used bright and emotional stimuli to evoke pupillary responses in tasks requiring reactive and voluntary saccade generation. Decreased voluntary saccade peak velocities, reduced tonic pupil size and phasic pupillary responses were observed as time-on-task increased. Moreover, tonic pupil size affected saccade latency and dynamics, with steeper saccade main sequence slope as tonic pupil size increased. In summary, saccade dynamics and tonic pupil size were sensitive to fatigue and arousal level, together providing valuable information for the understanding of human behavior. Full article

Eye-tracking can offer a novel clinical practice and a non-invasive tool to detect neuropathological syndromes. In this paper, we show some analysis on data obtained from the visual sequential search test. Indeed, such a test can be used to evaluate the capacity of looking at objects in a specific order, and its successful execution requires the optimization of the perceptual resources of foveal and extrafoveal vision. The main objective of this work is to detect if some patterns can be found within the data, to discern among people with chronic pain, extrapyramidal patients and healthy controls. We employed statistical tests to evaluate differences among groups, considering three novel indicators: blinking rate, average blinking duration and maximum pupil size variation. Additionally, to divide the three patient groups based on scan-path images—which appear very noisy and all similar to each other—we applied deep learning techniques to embed them into a larger transformed space. We then applied a clustering approach to correctly detect and classify the three cohorts. Preliminary experiments show promising results. Full article

The size of our pupils changes continuously in response to variations in ambient light levels, a process known as the pupillary light reflex (PLR). The PLR is not a simple reflex as its function is modulated by cognitive brain function and any long-term changes in brain function secondary to injury should cause a change in the parameters of the PLR. We performed a retrospective clinical review of the PLR of our patients using the BrightLamp Reflex iPhone app. The PLR variables of latency, maximum pupil diameter (MaxPD), minimum pupil diameter (MinPD), maximum constriction velocity (MCV), and the 75% recovery time (75% PRT) were associated with significant differences between subjects who had suffered a concussion and those that had not. There were also significant differences in PLR metrics over the life span and between genders and those subjects with and without symptoms. The differences in PLR metrics are modulated not only by concussion history but also by gender and whether or not the person has symptoms associated with a head injury. A concussive injury to the brain is associated with changes in the PLR that persist over the life span, representing biomarkers that might be used in clinical diagnosis, treatment, and decision making. Full article

As life expectancy grows, so too will the number of people adversely affected by age. Although it is acknowledged that many conditions and diseases are associated with age, this mini-review will present a current update of the various visual changes that generally occur in healthy individuals disregarding the possible effects of illness. These alterations influence how the world is perceived and in turn can affect efficiency or the ability to perform ordinary daily tasks such as driving or reading. The most common physical developments include a decreased pupil size and retinal luminance as well as changes both in intercellular and intracellular connections within the retina along the pathway to the visual cortex and within the visual cortex. The quantity and the physical location of retinal cells including photoreceptors, ganglion and bipolar retinal cells are modified. The clarity of intraocular organs, such as the intraocular lens, decreases. These all result in common visual manifestations that include reduced visual acuity, dry eyes, motility changes, a contraction of the visual field, presbyopia, reduced contrast sensitivity, slow dark adaptation, recovery from glare, variation in color vision and a decreased visual processing speed. Highlighting these prevalent issues as well as current and possible future innovations will assist providers to formulate treatments and thereby conserve maximum independence and mobility in the modern mature population. Full article

The pseudophakic eye lacks the ability to produce a refractive change in response to object proximity. Thus, individual anatomical features such as the pupil size play an important role in achieving functional vision levels. In this work, the range of pupil sizes at varying object distance was measured in pseudophakic participants. Furthermore, the impact of the measured values on eye optical quality was investigated using a computer simulation model. A binocular eye-tracker was used to measure the participants’ pupil sizes at six object distances, ranging from $0.33$ m (i.e., vergence of $3.00$ D) to $3.00$ m (i.e., vergence of $0.33$ D), while observing a Maltese cross with a constant angular size of $1^{\circ }$ . In total, 58 pseudophakic participants were enrolled in this study (age mean ± standard deviation: $70.5\pm 11.3$ years). The effects of object distance and age on pupil size variation were investigated using linear mixed effects regression models. Age was found to have a small contribution to individual variability. The mean infinite distance pupil size (intercept) was $4.45$ ( $95\%$ CI: 2.74, 6.17) mm and the mean proximal miosis (slope) was $-0.23$ ( $95\%$ CI: −0.53, 0.08) mm/D. The visual acuity (VA) estimation for a distant object ranged from $-0.1$ logMAR (smallest pupil) to $0.04$ logMAR (largest pupil) and the near VA ( $0.33$ m) when mean proximal miosis was considered ranged from $0.28$ logMAR (smallest pupil) to $0.42$ logMAR (largest pupil). When mean distance pupil was considered, proximal miosis individual variability produced a variation of $0.04$ logMAR for the near object and negligible variation for the distant object. These results support the importance of distance pupil size measurement for the prediction of visual performance in pseudophakia, while suggesting that proximal miosis has a negligible impact in VA variability. Full article

Pupil size informs about sympathovagal balance as well as cognitive and affective processes, and perception. It is also directly linked to phasic activity of the brainstem locus coeruleus, so that pupil measures have gained recent attention. Steady-state pupil size and its variability have been directly linked to sleep homeostasis and circadian phase, but results have been inconsistent. Here, we report robust changes in steady-state pupil size during 29 h of continuous wakefulness in healthy young men (N = 20; 18–30 years old) maintained in dim-light in strictly controlled constant routine conditions. These variations were associated with variations in motivation and sustained attention performance. Pupil size variability did not significantly change during the protocol. Yet, pupil size variability was linearly associated with subjective fatigue, sociability, and anguish. No associations were found between neither steady-state pupil size nor pupil size variability, and objective EEG measure of alertness and subjective sleepiness. Our data support therefore the notion that, compared with its variability, steady-state pupil size is strongly influenced by the concomitant changes in sleep need and circadian phase. In addition, steady-state pupil size appears to be related to motivation and attention, while its variability may be related to separate affective dimensions and subjective fatigue. Full article