Spontaneous eyeblink activity

Altered pupil light and darkness reflex and eye-blink responses in late-life depression

BACKGROUND

Late-life depression (LLD) is a prevalent neuropsychiatric disorder in the older population. While LLD exhibits high mortality rates, depressive symptoms in older adults are often masked by physical health conditions. In younger adults, depression is associated with deficits in pupil light reflex and eye blink rate, suggesting the potential use of these responses as biomarkers for LLD.

METHODS

We conducted a study using video-based eye-tracking to investigate pupil and blink responses in LLD patients (n = 25), older (OLD) healthy controls (n = 29), and younger (YOUNG) healthy controls (n = 25). The aim was to determine whether there were alterations in pupil and blink responses in LLD compared to both OLD and YOUNG groups.

RESULTS

LLD patients displayed significantly higher blink rates and dampened pupil constriction responses compared to OLD and YOUNG controls. While tonic pupil size in YOUNG differed from that of OLD, LLD patients did not exhibit a significant difference compared to OLD and YOUNG controls. GDS-15 scores in older adults correlated with light and darkness reflex response variability and blink rates. PHQ-15 scores showed a correlation with blink rates, while MoCA scores correlated with tonic pupil sizes.

CONCLUSIONS

The findings demonstrate that LLD patients display altered pupil and blink behavior compared to OLD and YOUNG controls. These altered responses correlated differently with the severity of depressive, somatic, and cognitive symptoms, indicating their potential as objective biomarkers for LLD.

The Effect of Ambient Illumination and Text Color on Visual Fatigue under Negative Polarity

This study investigates the effects of ambient illumination and negatively polarized text color on visual fatigue, exploring the issue of visual fatigue when using visual display terminals in low-illumination environments. The research methodology utilizes an experimental design to collect data on changes in pupil accommodation and blink rate through an eye tracker. Participants completed a reading task while exposed to various text colors and ambient light conditions to evaluate visual fatigue and cognitive performance. The study's findings suggest that text color significantly affects visual fatigue, with red text causing the highest level of visual fatigue and yellow text causing the lowest level of visual fatigue. Improvements in ambient lighting reduce visual fatigue, but the degree of improvement varies depending on the text color. Additionally, cognitive performance is better when using yellow and white text but worse when using red text. Yellow text is the most effective choice for reducing visual fatigue under negative polarity. Increasing ambient lighting can also improve visual fatigue in low-illumination conditions. These findings will offer valuable guidance for designing visual terminal device interfaces, especially for low-illumination or night environments, to minimize visual fatigue and improve user experience.

Blink Lagophthalmos in Graves Orbitopathy

PURPOSE

To investigate the relationship between the kinematics of spontaneous blinks and the anterior area of the levator palpebrae superioris muscle in patients with Graves orbitopathy (GO).

METHODS

This is a case-control study. The authors measured the margin reflex distance of the upper eyelid (margin reflex distance 1), the kinematics of spontaneous blinks, and the anterior area of levator palpebrae superioris muscle in CT coronal scans of patients with Graves upper eyelid retraction (GO) and a control group. The eye with the greatest margin reflex distance 1 was selected for analysis in each group.

RESULTS

A total of 68 participants were included, with 36 in the GO group and 32 in the control group. In the GO group, the mean margin reflex distance 1 measured 6.5 mm, while in the control group, it was 3.9 mm. Almost all parameters related to the closing phase of spontaneous blinking activity, including amplitude, velocity, blinking rate, and interblink time, did not differ between the two groups. However, the effectiveness of the blink's amplitude (ratio of blink amplitude to margin reflex distance 1) and the main sequence (relationship between amplitude and velocity) were significantly reduced in the GO group compared with the control group. The area of the levator palpebrae superioris muscle was significantly larger in GO than in controls, with 71.4% of patients' muscles outside of the maximum range of the controls.

CONCLUSIONS

In patients with GO, there is a reduction in blinking effectiveness, also known as blink lagophthalmos, which is a factor in the common occurrence of ocular surface symptoms. The increase in velocity with amplitude is also reduced in GO.

Neural control of blinking

Blinking is a motor act characterized by the sequential closing and opening of the eyelids, which is achieved through the reciprocal activation of the orbicularis oculi and levator palpebrae superioris muscles. This stereotyped movement can be triggered reflexively, occur spontaneously, or voluntarily initiated. During each type of blinking, the neural control of the antagonistic interaction between the orbicularis oculi and levator palpebrae superioris muscles is governed by partially overlapping circuits distributed across cortical, subcortical, and brainstem structures. This paper provides a comprehensive overview of the anatomical and physiological foundations underlying the neural control of blinking. We describe the infra-nuclear apparatus, as well as the supra-nuclear control mechanisms, i.e., how cortical, subcortical, and brainstem structures regulate and coordinate the different types of blinking.

Bionic blink improves real-time eye closure in unilateral facial paralysis

Facial paralysis is the inability to move facial muscles thereby impairing the ability to blink and make facial expressions. Depending on the localization of the nerve malfunction it is subcategorised into central or peripheral and is usually unilateral. This leads to health deficits stemming from corneal dryness and social ostracization.Objective: Electrical stimulation shows promise as a method through which to restore the blink function and as a result improve eye health. However, it is unknown whether a real-time, myoelectrically controlled, neurostimulating device can be used as assistance to this pathological condition.Approach: We developed NEURO-BLINK, a wearable robotic system, that can detect the volitional healthy contralateral blink through electromyography and electrically stimulate the impaired subcutaneous facial nerve and orbicularis oculi muscle to compensate for lost blink function. Alongside the system, we developed a method to evaluate optimal electrode placement through the relationship between blink amplitude and injected charge.Main results: Ten patients with unilateral facial palsy were enrolled in the NEURO-BLINK study, with eight completing testing under two conditions. (1) where the stimulation was cued with an auditory signal (i.e. paced controlled) and (2) synchronized with the natural blink (i.e. myoelectrically controlled). In both scenarios, overall eye closure (distance between eyelids) and cornea coverage measured with high FPS video were found to significantly improve when measured in real-time, while no significant clinical changes were found immediately after use.Significance: This work takes steps towards the development of a portable medical device for blink restoration and facial stimulation which has the potential to improve long-term ocular health.

What is a blink? Classifying and characterizing blinks in eye openness signals

Blinks, the closing and opening of the eyelids, are used in a wide array of fields where human function and behavior are studied. In data from video-based eye trackers, blink rate and duration are often estimated from the pupil-size signal. However, blinks and their parameters can be estimated only indirectly from this signal, since it does not explicitly contain information about the eyelid position. We ask whether blinks detected from an eye openness signal that estimates the distance between the eyelids (EO blinks) are comparable to blinks detected with a traditional algorithm using the pupil-size signal (PS blinks) and how robust blink detection is when data quality is low. In terms of rate, there was an almost-perfect overlap between EO and PS blink (F1 score: 0.98) when the head was in the center of the eye tracker's tracking range where data quality was high and a high overlap (F1 score 0.94) when the head was at the edge of the tracking range where data quality was worse. When there was a difference in blink rate between EO and PS blinks, it was mainly due to data loss in the pupil-size signal. Blink durations were about 60 ms longer in EO blinks compared to PS blinks. Moreover, the dynamics of EO blinks was similar to results from previous literature. We conclude that the eye openness signal together with our proposed blink detection algorithm provides an advantageous method to detect and describe blinks in greater detail.

Contact lens fitting and changes in the tear film dynamics: mathematical and computational models review

PURPOSE

This review explores mathematical models, blinking characterization, and non-invasive techniques to enhance understanding and refine clinical interventions for ocular conditions, particularly for contact lens wear.

METHODS

The review evaluates mathematical models in tear film dynamics and their limitations, discusses contact lens wear models, and highlights computational mechanical models. It also explores computational techniques, customization of models based on individual blinking dynamics, and non-invasive diagnostic tools like high-speed cameras and advanced imaging technologies.

RESULTS

Mathematical models provide insights into tear film dynamics but face challenges due to simplifications. Contact lens wear models reveal complex ocular physiology and design aspects, aiding in lens development. Computational mechanical models explore eye biomechanics, often integrating tear film dynamics into a Multiphysics framework. While different computational techniques have their advantages and disadvantages, non-invasive tools like OCT and thermal imaging play a crucial role in customizing these Multiphysics models, particularly for contact lens wearers.

CONCLUSION

Recent advancements in mathematical modeling and non-invasive tools have revolutionized ocular health research, enabling personalized approaches. The review underscores the importance of interdisciplinary exploration in the Multiphysics approach involving tear film dynamics and biomechanics for contact lens wearers, promoting advancements in eye care and broader ocular health research.

Exposure limits for indoor volatile substances concerning the general population: The role of population-based differences in sensory irritation of the eyes and airways for assessment factors

Assessment factors (AFs) are essential in the derivation of occupational exposure limits (OELs) and indoor air quality guidelines. The factors shall accommodate differences in sensitivity between subgroups, i.e., workers, healthy and sick people, and occupational exposure versus life-long exposure for the general population. Derivation of AFs itself is based on empirical knowledge from human and animal exposure studies with immanent uncertainty in the empirical evidence due to knowledge gaps and experimental reliability. Sensory irritation in the eyes and airways constitute about 30-40% of OELs and is an abundant symptom in non-industrial buildings characterizing the indoor air quality and general health. Intraspecies differences between subgroups of the general population should be quantified for the proposal of more 'empirical' based AFs. In this review, we focus on sensitivity differences in sensory irritation about gender, age, health status, and vulnerability in people, based solely on human exposure studies. Females are more sensitive to sensory irritation than males for few volatile substances. Older people appear less sensitive than younger ones. However, impaired defense mechanisms may increase vulnerability in the long term. Empirical evidence of sensory irritation in children is rare and limited to children down to the age of six years. Studies of the nervous system in children compared to adults suggest a higher sensitivity in children; however, some defense mechanisms are more efficient in children than in adults. Usually, exposure studies are performed with healthy subjects. Exposure studies with sick people are not representative due to the deselection of subjects with moderate or severe eye or airway diseases, which likely underestimates the sensitivity of the group of people with diseases. Psychological characterization like personality factors shows that concentrations of volatile substances far below their sensory irritation thresholds may influence the sensitivity, in part biased by odor perception. Thus, the protection of people with extreme personality traits is not feasible by an AF and other mitigation strategies are required. The available empirical evidence comprising age, lifestyle, and health supports an AF of not greater than up to 2 for sensory irritation. Further, general AFs are discouraged for derivation, rather substance-specific derivation of AFs is recommended based on the risk assessment of empirical data, deposition in the airways depending on the substance's water solubility and compensating for knowledge and experimental gaps. Modeling of sensory irritation would be a better 'empirical' starting point for derivation of AFs for children, older, and sick people, as human exposure studies are not possible (due to ethical reasons) or not generalizable (due to self-selection). Dedicated AFs may be derived for environments where dry air, high room temperature, and visually demanding tasks aggravate the eyes or airways than for places in which the workload is balanced, while indoor playgrounds might need other AFs due to physical workload and affected groups of the general population.

Eye blinking, musical processing, and subjective states-A methods account

Affective sciences often make use of self-reports to assess subjective states. Seeking a more implicit measure for states and emotions, our study explored spontaneous eye blinking during music listening. However, blinking is understudied in the context of research on subjective states. Therefore, a second goal was to explore different ways of analyzing blink activity recorded from infra-red eye trackers, using two additional data sets from earlier studies differing in blinking and viewing instructions. We first replicate the effect of increased blink rates during music listening in comparison with silence and show that the effect is not related to changes in self-reported valence, arousal, or to specific musical features. Interestingly, but in contrast, felt absorption reduced participants' blinking. The instruction to inhibit blinking did not change results. From a methodological perspective, we make suggestions about how to define blinks from data loss periods recorded by eye trackers and report a data-driven outlier rejection procedure and its efficiency for subject-mean analyses, as well as trial-based analyses. We ran a variety of mixed effects models that differed in how trials without blinking were treated. The main results largely converged across accounts. The broad consistency of results across different experiments, outlier treatments, and statistical models demonstrates the reliability of the reported effects. As recordings of data loss periods come for free when interested in eye movements or pupillometry, we encourage researchers to pay attention to blink activity and contribute to the further understanding of the relation between blinking, subjective states, and cognitive processing.

Monitoring Blinks And Eyelid Twitches In Horses To Assess Stress During The Samples Collection Process

To assess stress in horses, a method of monitoring eye blinks (full and half) and eyelid twitches while collecting saliva and blood samples before and after annual intensive police training was carried out. This noninvasive monitoring method was used to determine whether blood collection, which is considered invasive, is more stressful for horses than saliva collection. We discovered no significant difference in stress related manifestations between saliva sampling and blood collection in our study. In both cases, sampling (blood and saliva) reduced the number of full and half eye blinks. Based on our hypothesis, we expected a statistically significant changes in the number of eye blinks and eyelid twitches as the number of potential stressors increased (in our case, we considered police training and sampling). Saliva cortisol levels, on the other hand, revealed that police training for horses was not stressful. The method of measuring eye blinks and eyelid twitches appears to be an appropriate alternative method for monitoring stress factors in horses.

Loss of Blink Regularity and Its Impact on Ocular Surface Exposure

(1) Background: Changes in blink parameters have been found to influence ocular surface exposure, eliciting symptoms of dry eye and ocular signs. The aim of the study was to highlight the relevance of including blink regularity as a new parameter to fully characterize blinking; (2) Methods: A novel characterization of blink parameters is described, including spontaneous eyeblink rate (SEBR), percentage of incomplete blinks, and blink regularity. A pilot study was designed in which tear film break-up time (TFBUT), blink parameters, and the time percentage of ocular surface exposure were determined in eight subjects (52.0 ± 16.6 years, 4 females) in three experimental conditions (baseline, reading a hard-copy text, and reading from an electronic display). Blink parameters were monitored through asynchronous image analysis of one minute video segments; (3) Results: All blink parameters were influenced by experimental conditions. A trend was observed in which both reading tasks resulted in an increase in ocular surface exposure, mainly related to a combination of reduced SEBR, increased percentage of incomplete blinks, and loss of blink regularity; (4) Conclusions: A complete characterization of blink parameters is relevant to better understand ocular dryness related to surface exposure and to advice patients towards a reeducation of their blinking habits.

Motor synchronization and impulsivity in pediatric borderline personality disorder with and without attention-deficit hyperactivity disorder: an eye-tracking study of saccade, blink and pupil behavior

Shifting motor actions from reflexively reacting to an environmental stimulus to predicting it allows for smooth synchronization of behavior with the outside world. This shift relies on the identification of patterns within the stimulus - knowing when a stimulus is predictable and when it is not - and launching motor actions accordingly. Failure to identify predictable stimuli results in movement delays whereas failure to recognize unpredictable stimuli results in early movements with incomplete information that can result in errors. Here we used a metronome task, combined with video-based eye-tracking, to quantify temporal predictive learning and performance to regularly paced visual targets at 5 different interstimulus intervals (ISIs). We compared these results to the random task where the timing of the target was randomized at each target step. We completed these tasks in female pediatric psychiatry patients (age range: 11-18 years) with borderline personality disorder (BPD) symptoms, with (n = 22) and without (n = 23) a comorbid attention-deficit hyperactivity disorder (ADHD) diagnosis, against controls (n = 35). Compared to controls, BPD and ADHD/BPD cohorts showed no differences in their predictive saccade performance to metronome targets, however, when targets were random ADHD/BPD participants made significantly more anticipatory saccades (i.e., guesses of target arrival). The ADHD/BPD group also significantly increased their blink rate and pupil size when initiating movements to predictable versus unpredictable targets, likely a reflection of increased neural effort for motor synchronization. BPD and ADHD/BPD groups showed increased sympathetic tone evidenced by larger pupil sizes than controls. Together, these results support normal temporal motor prediction in BPD with and without ADHD, reduced response inhibition in BPD with comorbid ADHD, and increased pupil sizes in BPD patients. Further these results emphasize the importance of controlling for comorbid ADHD when querying BPD pathology.

Highly reproducible eyeblink timing during formula car driving

How do humans blink while driving a vehicle? Although gaze control patterns have been previously reported in relation to successful steering, eyeblinks that disrupt vision are believed to be randomly distributed during driving or are ignored. Herein, we demonstrate that eyeblink timing shows reproducible patterns during real formula car racing driving and is related to car control. We studied three top-level racing drivers. Their eyeblinks and driving behavior were acquired during practice sessions. The results revealed that the drivers blinked at surprisingly similar positions on the courses. We identified three factors underlying the eyeblink patterns: the driver's individual blink count, lap pace associated with how strictly they followed their pattern on each lap, and car acceleration associated with when/where to blink at a moment. These findings suggest that the eyeblink pattern reflected cognitive states during in-the-wild driving and experts appear to change such cognitive states continuously and dynamically.

Carbohydrate polymer-based bioadhesive formulations and their potentials for the treatment of ocular diseases: A review

Eyes are directly exposed to the outer environment and susceptible to infections, leading to various ocular disorders. Local medication is preferred to treat eye diseases due to its convenience and compliance. However, the rapid clearance of the local formulations highly limits the therapeutic efficacy. In the past decades, several carbohydrate bioadhesive polymers (CBPs), such as chitosan and hyaluronic acid, have been used in ophthalmology for sustained ocular drug delivery. These CBP-based delivery systems have improved the treatment of ocular diseases to a large extent but also caused some undesired effects. Herein, we aim to summarize the applications of some typical CBPs (including chitosan, hyaluronic acid, cellulose, cyclodextrin, alginate and pectin) in treating ocular diseases from the general view of ocular physiology, pathophysiology and drug delivery, and to provide a comprehensive understanding of the design of the CBP-based formulations for ocular use. The patents and clinical trials of CBPs for ocular management are also discussed. In addition, a discussion on the concerns of CBPs in clinical use and the possible solutions is presented.

A scoping review of eye tracking metrics used to assess visuomotor behaviours of upper limb prosthesis users

Advanced upper limb prostheses aim to restore coordinated hand and arm function. However, this objective can be difficult to quantify as coordinated movements require an intact visuomotor system. Eye tracking has recently been applied to study the visuomotor behaviours of upper limb prosthesis users by enabling the calculation of eye movement metrics. This scoping review aims to characterize the visuomotor behaviours of upper limb prosthesis users as described by eye tracking metrics, to summarize the eye tracking metrics used to describe prosthetic behaviour, and to identify gaps in the literature and potential areas for future research. A review of the literature was performed to identify articles that reported eye tracking metrics to evaluate the visual behaviours of individuals using an upper limb prosthesis. Data on the level of amputation, type of prosthetic device, type of eye tracker, primary eye metrics, secondary outcome metrics, experimental task, aims, and key findings were extracted. Seventeen studies were included in this scoping review. A consistently reported finding is that prosthesis users have a characteristic visuomotor behaviour that differs from that of individuals with intact arm function. Visual attention has been reported to be directed more towards the hand and less towards the target during object manipulation tasks. A gaze switching strategy and delay to disengage gaze from the current target has also been reported. Differences in the type of prosthetic device and experimental task have revealed some distinct gaze behaviours. Control factors have been shown to be related to gaze behaviour, while sensory feedback and training interventions have been demonstrated to reduce the visual attention associated with prosthesis use. Eye tracking metrics have also been used to assess the cognitive load and sense of agency of prosthesis users. Overall, there is evidence that eye tracking is an effective tool to quantitatively assess the visuomotor behaviour of prosthesis users and the recorded eye metrics are sensitive to change in response to various factors. Additional studies are needed to validate the eye metrics used to assess cognitive load and sense of agency in upper limb prosthesis users.

Global motion processing in infants' visual cortex and the emergence of autism

Autism is a heritable and common neurodevelopmental condition, with behavioural symptoms typically emerging around age 2 to 3 years. Differences in basic perceptual processes have been documented in autistic children and adults. Specifically, data from many experiments suggest links between autism and alterations in global visual motion processing (i.e., when individual motion information is integrated to perceive an overall coherent pattern). Yet, no study has investigated whether a distinctive organization of global motion processing precede the emergence of autistic symptoms in early childhood. Here, using a validated infant electroencephalography (EEG) experimental paradigm, we first establish the normative activation profiles for global form, global motion, local form, and local motion in the visual cortex based on data from two samples of 5-month-old infants (total n = 473). Further, in a sample of 5-month-olds at elevated likelihood of autism (n = 52), we show that a different topographical organization of global motion processing is associated with autistic symptoms in toddlerhood. These findings advance the understanding of neural organization of infants' basic visual processing, and its role in the development of autism.

Effects of cataract surgery on blinking

PURPOSE

To assess the effects of cataract surgery on the spontaneous blinking pattern and blinking kinematics.

SETTING

FISABIO Oftalmología Médica Eye Hospital, Valencia, Spain.

DESIGN

Observational descriptive clinical study.

METHOD

Patients with senile cataract were evaluated before (visit 1) and at 1 month (visit 2) and 3 months (visit 3) after undergoing phacoemulsification cataract surgery. The blinking of patients was recorded for 90 seconds using an eye-tracking device. Blinks were analyzed by means of image analysis to obtain a noninvasive detailed description of blinking including blink rate, number of complete and incomplete blinks, percentage of incomplete blinks, and kinematic parameters, including amplitude, closing, contact, opening, and total durations and closing and opening speeds.

RESULTS

50 patients were included in this study. The blink rate was significantly smaller at visit 3 compared with baseline ( P = .03) and visit 2 ( P = .001). Likewise, the number of complete blinks was significantly smaller, and the percentage of incomplete blinks was significantly higher at 3 months postoperatively compared with baseline ( P = .02 and P = .01, respectively), although no differences were observed at 1 month postoperatively ( P > .05). Conversely, no differences in the number of incomplete blinks or any kinematic parameter were observed between visits ( P = .12).

CONCLUSIONS

Cataract surgery significantly altered the blinking pattern at 3 months postoperatively, although kinematic parameters remained unvaried. Clinicians should be aware of potential alterations in blinking after phacoemulsification cataract surgery and the implications this may have on the ocular surface of patients.

Video-based eye blink identification and classification

Blink detection and classification can provide a very useful clinical indicator, because of its relation with many neurological and ophthalmological conditions. In this work, we propose a system that automatically detects and classifies blinks as "complete" or "incomplete" in high resolution image sequences zoomed into the participants' face, acquired during clinical examination using near-Infrared illumination. This method utilizes state-of-the-art (DeepLabv3+) deep learning encoder-decoder neural architecture-DLED to segment iris and eyelid in both eyes in the acquired images. The sequence of the segmented frames is post-processed to calculate the distance between the eyelids of each eye (palpebral fissure height) and the corresponding iris diameter. Theses quantities are temporally filtered and their fraction is subject to adaptive thresholding to identify blinks and determine their type, independently for each eye. The proposed system was tested on 15 participants, each with one video of 4 to 10 minutes. Several metrics of blink detection and classification accuracy were calculated against the ground truth, which was generated by three (3) independent experts, whose conflicts were resolved by a senior expert. Results show that the proposed system achieved F1-score 95.3% and 80.9% for the classification of complete and incomplete blinks respectively, collectively for all 15 participants, outperforming all 3 experts. The proposed system was proven robust in handling unexpected participant movements and actions, as well as glare and reflections from the spectacles, or face obstruction by facemasks.

Let Complexity Bring Clarity: A Multidimensional Assessment of Cognitive Load Using Physiological Measures

The effects of cognitive load on driver behavior and traffic safety are unclear and in need of further investigation. Reliable measures of cognitive load for use in research and, subsequently, in the development and implementation of driver monitoring systems are therefore sought. Physiological measures are of interest since they can provide continuous recordings of driver state. Currently, however, a few issues related to their use in this context are not usually taken into consideration, despite being well-known. First, cognitive load is a multidimensional construct consisting of many mental responses (cognitive load components) to added task demand. Yet, researchers treat it as unidimensional. Second, cognitive load does not occur in isolation; rather, it is part of a complex response to task demands in a specific operational setting. Third, physiological measures typically correlate with more than one mental state, limiting the inferences that can be made from them individually. We suggest that acknowledging these issues and studying multiple mental responses using multiple physiological measures and independent variables will lead to greatly improved measurability of cognitive load. To demonstrate the potential of this approach, we used data from a driving simulator study in which a number of physiological measures (heart rate, heart rate variability, breathing rate, skin conductance, pupil diameter, eye blink rate, eye blink duration, EEG alpha power, and EEG theta power) were analyzed. Participants performed a cognitively loading n-back task at two levels of difficulty while driving through three different traffic scenarios, each repeated four times. Cognitive load components and other coinciding mental responses were assessed by considering response patterns of multiple physiological measures in relation to multiple independent variables. With this approach, the construct validity of cognitive load is improved, which is important for interpreting results accurately. Also, the use of multiple measures and independent variables makes the measurements (when analyzed jointly) more diagnostic-that is, better able to distinguish between different cognitive load components. This in turn improves the overall external validity. With more detailed, diagnostic, and valid measures of cognitive load, the effects of cognitive load on traffic safety can be better understood, and hence possibly mitigated.

Multiple levels of mental attentional demand modulate peak saccade velocity and blink rate

Every day we mentally process new information that needs to be attended, encoded and retrieved. Processing demands depend on the amount of information and the mental attentional capacity of the individual. Research shows that eye movement indices such as peak saccade velocity and blink rate are related to processes of attentional control, however it is still unclear how eye movements are affected by graded changes in task demand. We examine for the first time relations of eye movements to mental attentional tasks with six levels of task demand and two interference conditions. We report data on 57 adults who completed two versions of the color matching task and provided subjective self rating for each mental attentional demand level. Results show that peak saccade velocity and blink rate decrease as a function of mental attentional demand and correlate negatively with self rating of mental effort. Theoretically, new findings related to mental attentional demand and eye movements inform models of visual processing and cognition. Practically, results point to directions for further research to better understand complex relations among eye movements and mental attentional demand in pediatric populations and individuals with cognitive deficits.

Patterns of eye blinks are modulated by auditory input in humans

Previous studies could elaborate a link between attentional processes and eye blinking in both visual and auditory attention tasks. Here we show that this link is active at a fundamental level of perception: presentation of a series of bare sine tones is sufficient to induce a modulation of temporal blink patterns, allowing to determine which series was presented to participants even when they are not required to interactively engage in processing the auditory input. In particular, we monitored eye blinking during an auditory attention task using two series of sine tones, differing in the predictability of the timing of tone onsets. Whereas inter-onset intervals in one tone series corresponded to uncorrelated samples from a normal distribution, they were distributed according to a Gaussian random walk in the other tone series. We find that blink patterns are dynamically modulated by both purely auditory inputs. The magnitude, form, and coherence of the temporal associations between tone onsets and blink events depend strongly on the requirement to respond to the presented stimuli. The predictability of the tone series appears to modulate pre-stimulus blink inhibition given that a response is required. Altogether, these findings suggest eye blink as a readily available, non-invasive behavioral marker for context-sensitive, moment-to-moment allocation of attention.

Effect of Transcutaneous Upper Eyelid Blepharoplasty on Blink Parameters and Lipid Layer Thickness

Purpose: This study aimed to investigate the effect of transcutaneous upper eyelid blepharoplasty on lipid layer thickness (LLT) and blink parameters in young women during the early postoperative period.

Methods: This prospective study included 110 eyes of 55 young female patients (age range, 19–31 years) who underwent transcutaneous upper eyelid blepharoplasty. The LLT and blink parameters measured using a LipiView interferometer were recorded before the surgery and 1 week and 1 month after the surgery. Ocular Surface Disease Index (OSDI) score, noninvasive tear film breakup time (NITBUT), and palpebral fissure height (PFH) measurements were also performed at each time point.

Results: The number of blinks significantly decreased (P < 0.001), and the number of partial blinks and partial blink rate (PBR) significantly increased 1 week after the surgery (P = 0.002 and P < 0.001); they all returned to baseline in 1 month. The LLT and OSDI score increased significantly 1 week and 1 month after the surgery (P < 0.001 and P < 0.001). A significant increase in the NITBUT and a significant decrease in the PFH were observed 1 week after the surgery (P < 0.001 and P < 0.001), and the values returned to baseline 1 month after the surgery. No clinical correlation was found between blink parameters and ocular surface parameters.

Conclusions: Transcutaneous upper eyelid blepharoplasty led to a change in blink parameters and ocular surface parameters during the early postoperative period. However, this influence was temporary, and the transitory change in blink parameters had no effects on the ocular surface environment.

Blinking kinematics characterization during digital displays use

Purpose

This study aimed to assess the differences in blinking kinematics while reading on different digital displays and a control condition.

Methods

Thirty-two young healthy individuals were included in this prospective clinical study. The blinks of subjects were recorded for 150 s while reading on a laptop computer, tablet, e-reader, and smartphone and a control condition. Blinks were recorded using an eye-tracking device and were analyzed by means of image analysis to obtain a non-invasive detailed description of the blink movement.

Results

Blink rate decreased when reading on all displays compared to the control (p < 0.0005), although no differences were obtained amongst displays (p > 0.05). The percentage of incomplete blinks was higher with the computer compared to the control (p = 0.043), and lower with the smartphone compared to the rest of the conditions (p ≤ 0.015). Blink amplitude was smaller when reading from handheld devices compared to the control (p < 0.0005) and the computer (p ≤ 0.048). Closing and opening blink durations remained unvaried amongst conditions (p > 0.05), while opening and closing speeds were greater for the control and the computer compared to the handheld displays (p < 0.0005). Finally, contact and total blink durations were shorter during computer reading compared to the control (p = 0.004 and p = 0.017, respectively).

Conclusion

Blinking kinematics vary considerably amongst displays and with respect to baseline, with these differences being probably attributed to differences in the way the displays are set up and the cognitive demand of the task.

Comparative Blink Analysis in Patients With Established Facial Paralysis Using High-Speed Video Analysis

ABSTRACT

This study analyzed the blink characteristics of patients with incomplete and complete facial paralysis. The authors measured and compared the palpebral distance, eyelid movement distance, and the eye-closing ratio of blinks in 55 patients with Bell's palsy or Ramsay Hunt syndrome (Bell & Hunt group) and 14 with complete paralysis (Complete Paralysis group). In the Bell & Hunt group, the palpebral distance (7.94 mm) was smaller on the paralyzed side than on the non-paralyzed side (9.61 mm). The eye-closing ratio and the upper eyelid movement were reduced on the paralyzed side (65.3% versus 93.7%, 4.61 versus 7.97 mm) and in the Complete Paralysis group (25.3% versus 94.7%, 2.10 versus 8.49 mm). In the Bell & Hunt group, movement of the upper eyelid on the paralyzed side was weakened despite palpebral contracture. The Complete Paralysis group exhibited highly reduced movement in both the upper and lower eyelids.

Fluctuations in Arousal Correlate with Neural Activity in the Human Thalamus

The neural basis of consciousness has been explored in humans and animals; however, the exact nature of consciousness remains elusive. In this study, we aimed to elucidate which brain regions are relevant to arousal in humans. Simultaneous recordings of brain activity and eye-tracking were conducted in 20 healthy human participants. Brain activity was measured by resting-state functional magnetic resonance imaging with a multiband acquisition protocol. The subjective levels of arousal were investigated based on the degree of eyelid closure that was recorded using a near-infrared eye camera within the scanner. The results showed that the participants were in an aroused state for 79% of the scan time, and the bilateral thalami were significantly associated with the arousal condition. Among the major thalamic subnuclei, the mediodorsal nucleus (MD) showed greater involvement in arousal when compared with other subnuclei. A receiver operating characteristic analysis with leave-one-out crossvalidation conducted using template-based brain activity and arousal-level data from eye-tracking showed that, in most participants, thalamic activity significantly predicted the subjective levels of arousal. These results indicate a significant role of the thalamus, and in particular, the MD, which has rich connectivity with the prefrontal cortices and the limbic system in human consciousness.

Facial nerve paralysis: A review on the evolution of implantable prosthesis in restoring dynamic eye closure

Facial nerve paralysis (FNP) is a debilitating condition that leaves those affected with disfigurement and loss of function. The most important function of the facial nerve is protecting the eye through eye closure and blinking. A series of reanimation techniques have been reported to restore dynamic function in FNP, but the lack of a universally accepted method that is reliable and reproducible with immediate effect has led to the introduction of several implantable devices. Most of these devices have been applied to assist blinking; however, the delicate anatomy and unique mechanics of eye closure are difficult to replicate. Lid loading is the most frequently used implant today, which is a passive device that can aid in volitional eye closure but has a limited effect on blinking. Dynamic action can be achieved with active prostheses but achieving successful long-term function remains elusive. Device action must also be coupled with a real-time feedback mechanism in order to capture the natural variation in facial muscle movements. This review discusses all prostheses used for restoring eye closure and blinking to date and explores their relative merits.

The Relationship Between Dry Eye Disease and Digital Screen Use

Dry eye disease is characterized by tear film instability that can result in ocular surface damage. Patients with dry eye disease may experience ocular pain/discomfort and visual disturbances that may negatively impact quality of life. Increased use of digital screens for work, communication, and entertainment, especially during times of pandemic, may contribute to dry eye. Extensive cross-sectional studies have shown that digital screen use duration is associated with an increased risk of severe symptoms and clinical diagnosis of dry eye disease in adults. Smartphone use duration has also been found to be greater in school-age children with dry eye disease than in those without dry eye disease. A commonly accepted hypothesis for the relationship between digital screen use and dry eye disease is that digital screen use changes blinking dynamics, leading to ocular dryness. This review describes evidence that digital screen use is associated with dry eye disease, that digital device use alters blinking dynamics, and that dry eye affects mental health and work productivity in digital screen users. Helpful prevention and management strategies for dry eye disease exist for those who use digital screens.

Resolving visual motion through perceptual gaps

Perceptual gaps can be caused by objects in the foreground temporarily occluding objects in the background or by eyeblinks, which briefly but frequently interrupt visual information. Resolving visual motion across perceptual gaps is particularly challenging, as object position changes during the gap. We examine how visual motion is maintained and updated through externally driven (occlusion) and internally driven (eyeblinks) perceptual gaps. Focusing on both phenomenology and potential mechanisms such as suppression, extrapolation, and integration, we present a framework for how perceptual gaps are resolved over space and time. We finish by highlighting critical questions and directions for future work.

Physiological fluid interfaces: Functional microenvironments, drug delivery targets, and first line of defense

Fluid interfaces, i.e. the boundary layer of two liquids or a liquid and a gas, play a vital role in physiological processes as diverse as visual perception, oral health and taste, lipid metabolism, and pulmonary breathing. These fluid interfaces exhibit a complex composition, structure, and rheology tailored to their individual physiological functions. Advances in interfacial thin film techniques have facilitated the analysis of such complex interfaces under physiologically relevant conditions. This allowed new insights on the origin of their physiological functionality, how deviations may cause disease, and has revealed new therapy strategies. Furthermore, the interactions of physiological fluid interfaces with exogenous substances is crucial for understanding certain disorders and exploiting drug delivery routes to or across fluid interfaces. Here, we provide an overview on fluid interfaces with physiological relevance, namely tear films, interfacial aspects of saliva, lipid droplet digestion and storage in the cell, and the functioning of lung surfactant. We elucidate their structure-function relationship, discuss diseases associated with interfacial composition, and describe therapies and drug delivery approaches targeted at fluid interfaces. STATEMENT OF SIGNIFICANCE: Fluid interfaces are inherent to all living organisms and play a vital role in various physiological processes. Examples are the eye tear film, saliva, lipid digestion & storage in cells, and pulmonary breathing. These fluid interfaces exhibit complex interfacial compositions and structures to meet their specific physiological function. We provide an overview on physiological fluid interfaces with a focus on interfacial phenomena. We elucidate their structure-function relationship, discuss diseases associated with interfacial composition, and describe novel therapies and drug delivery approaches targeted at fluid interfaces. This sets the scene for ocular, oral, or pulmonary surface engineering and drug delivery approaches.

Sparsely Wiring Connectivity in the Upper Beta Band Characterizes the Brains of Top Swimming Athletes

Human brains are extremely energy costly in neural connections and activities. However, it is unknown what is the difference in the brain connectivity between top athletes with long-term professional trainings and age-matched controls. Here we ask whether long-term training can lower brain-wiring cost while have better performance. Since elite swimming requires athletes to move their arms and legs at different tempos in time with high coordination skills, we selected an eye-hand-foot complex reaction (CR) task to examine the relations between the task performance and the brain connections and activities, as well as to explore the energy cost-efficiency of top athletes. Twenty-one master-level professional swimmers and 23 age-matched non-professional swimmers as controls were recruited to perform the CR task with concurrent 8-channel EEG recordings. Reaction time and accuracy of the CR task were recorded. Topological network analysis of various frequency bands was performed using the phase lag index (PLI) technique to avoid volume conduction effects. The wiring number of connections and mean frequency were calculated to reflect the wiring and activity cost, respectively. Results showed that professional athletes demonstrated better eye-hand-foot coordination than controls when performing the CR task, indexing by faster reaction time and higher accuracy. Comparing to controls, athletes' brain demonstrated significantly less connections and weaker correlations in upper beta frequency band between the frontal and parietal regions, while demonstrated stronger connectivity in the low theta frequency band between sites of F3 and Cz/C4. Additionally, athletes showed highly stable and low eye-blinking rates across different reaction performance, while controls had high blinking frequency with high variance. Elite athletes' brain may be characterized with energy efficient sparsely wiring connections in support of superior motor performance and better cognitive performance in the eye-hand-foot complex reaction task.

Analysis of Eyelid Blink Characteristics in Patients with Ptosis Using a Smartphone Camera

Purpose: To compare eyelid blink characteristics between patients with ptosis and healthy controls using a smartphone camera. Methods: The ptosis group consisted of 20 senile aponeurotic ptosis patients with margin reflex distance1 ≤2.5 mm and the control group consisted of 10 healthy subjects without ptosis. The ptosis group was further divided into two groups based on an age cutoff of 70 years. Palpebral fissure height, levator function, margin reflex distance1, inter-blink interval, blink duration, blink rate, and blink velocity were measured and compared between the three groups based on photographs of the eyelids and videos of blinking taken with a smartphone camera. Results: The palpebral fissure height, levator function, margin reflex distance1, and blink velocity were lower in the ptosis groups than in the control group but these values did not differ between the two ptosis groups. The palpebral fissure height, levator function, and margin reflex distance1 were correlated with blink velocity. In the receiver operating characteristic (ROC) curve of blink velocity, the area under the receiver operating characteristic (AUROC) curve value was as high as 0.969 and the cut-off value was 32.36 mm/s. Conclusions: It is possible to analyze eyelid blink characteristics using a smartphone camera and the results confirmed that palpebral fissure height, levator function, margin reflex distance1, and blink velocity were lower in the senile aponeurotic ptosis group than in the healthy control group and were unaffected by age. Additionally, blink velocity is valuable for diagnosis of ptosis due to the correlation between the degree of ptosis, blink velocity, and the ROC curve of blink velocity.

Spontaneous Eye Blinks Predict Executive Functioning in Seniors

As the world’s population is aging rapidly, cognitive training is an extensively used approach to attempt improvement of age-related cognitive functioning. With increasing numbers of older adults required to remain in the workforce, it is important to be able to reliably predict future functional decline, as well as the individual advantages of cognitive training. Given the correlation between age-related decline and striatal dopaminergic function, we investigated whether eye blink rate (EBR), a non-invasive, indirect indicator of dopaminergic activity, could predict executive functioning (response inhibition, switching and working memory updating) as well as trainability of executive functioning in older adults. EBR was collected before and after a cognitive flexibility training, cognitive training without flexibility, or a mock training. EBR predicted working memory updating performance on two measures of updating, as well as trainability of working memory updating, whereas performance and trainability in inhibition and switching tasks could not be predicted by EBR. Our findings tentatively indicate that EBR permits prediction of working memory performance in older adults. To fully interpret the relationship with executive functioning, we suggest future research should assess both EBR and dopamine receptor availability among seniors.

Dynamics and mechanisms for tear breakup (TBU) on the ocular surface

The human tear film is rapidly established after each blink, and is essential for clear vision and eye health. This paper reviews mathematical models and theories for the human tear film on the ocular surface, with an emphasis on localized flows where the tear film may fail. The models attempt to identify the important physical processes, and their parameters, governing the tear film in health and disease.

Systematic Comparison of Trial Exclusion Criteria for Pupillometry Data Analysis in Individuals With Single-Sided Deafness and Normal Hearing

The measurement of pupil dilation has become a common way to assess listening effort. Pupillometry data are subject to artifacts, requiring highly contaminated data to be discarded from analysis. It is unknown how trial exclusion criteria impact experimental results. The present study examined the effect of a common exclusion criterion, percentage of blinks, on speech intelligibility and pupil dilation measures in 9 participants with single-sided deafness (SSD) and 20 participants with normal hearing. Participants listened to and repeated sentences in quiet or with speech maskers. Pupillometry trials were processed using three levels of blink exclusion criteria: 15%, 30%, and 45%. These percentages reflect a threshold for missing data points in a trial, where trials that exceed the threshold are excluded from analysis. Results indicated that pupil dilation was significantly greater and intelligibility was significantly lower in the masker compared with the quiet condition for both groups. Across-group comparisons revealed that speech intelligibility in the SSD group decreased significantly more than the normal hearing group from quiet to masker conditions, but the change in pupil dilation was similar for both groups. There was no effect of blink criteria on speech intelligibility or pupil dilation results for either group. However, the total percentage of blinks in the masker condition was significantly greater than in the quiet condition for the SSD group, which is consistent with previous studies that have found a relationship between blinking and task difficulty. This association should be carefully considered in future experiments using pupillometry to gauge listening effort.

Internet Usage Habits and Experienced Levels of Psychopathology: A Pilot Study on Association with Spontaneous Eye Blinking Rate

Increasing availability of the internet has resulted in the increased prevalence of problematic online behaviors. Reliable and affordable neurobiological and psychological biomarkers that distinguish problematic internet use (PIU) from functional online activities are of utmost importance. Previous studies have shown a relationship between spontaneous eye blinking rate (sEBR) and changes in dopamine regulation in neurological and psychiatric disorders, including substance use disorders. In this study, we utilized sEBR to examine the potential link between individual differences in dopaminergic neurotransmission and PIU. In sum, 62 subjects participated in this study (median age 25, IQR 6 years, 34 females). The Problematic Internet Use Questionnaire (PIUQ-9), Beck Depression Inventory (BDI-II), Beck Anxiety Inventory (BAI), Clark-Beck Obsessive-Compulsive Inventory (CBOCI) and Barratt Impulsiveness Scale (BIS-11) were used for psychological assessment. The sEBRs were assessed with an electrooculogram recorded from above and below the left eye and from the right and left outer canthi. The group with PIU (PIUQ-9 > 20) expressed higher levels of impulsivity and compulsive behavior symptoms than the control group. In the group with PIU, impulsivity levels were inversely related to sEBR, and a trend of negative association of sEBR with compulsive behavior was observed. Future research should enroll subjects with high levels of PIU and strongly expressed psychopathology levels to further address the utility of sEBR as a potential biomarker.

Monitoring of Stress in Police Horses

Every year, police horses undergo police training focused on passing difficult obstacles, during which their physical and mental abilities are tested. Using a method of eye movement monitoring, specifically eye blinking and eyelid twitching, we estimated if the training of horses was stressful. The results we found suggested that the training itself, per se does not affect the welfare of police horses; as it is not stressful for them because the gradual training allows the horses to adapt to different types of work or physical activity.

Macaque monkey trigeminal blink reflex circuits targeting orbicularis oculi motoneurons

The trigeminal blink reflex plays an important role in protecting the corneal surface from damage and preserving visual function in an unpredictable environment. The closing phase of the human reflex, produced by activation of the orbicularis oculi (ObOc) muscles, consists of an initial, small, ipsilateral R₁ component, followed by a larger, bilateral R₂ component. We investigated the circuitry that underlies this reflex in macaque (Macaca fascicularis and Macaca mulatta) monkeys by the use of single and dual tracer methods. Injection of retrograde tracer into the facial nucleus labeled neurons in the principal trigeminal nucleus, and in the spinal nucleus pars oralis and interpolaris, bilaterally, and in pars caudalis, ipsilaterally. Injection of anterograde tracer into the principal trigeminal nucleus labeled axons that directly terminated on ObOc motoneurons, with an ipsilateral predominance. Injection of anterograde tracer into pars caudalis of the spinal trigeminal nucleus labeled axons that directly terminated on ipsilateral ObOc motoneurons. The observed pattern of labeling indicates that the reticular formation ventromedial to the principal and spinal nuclei also contributes extensive bilateral input to ObOc motoneurons. Thus, much of the trigeminal sensory complex is in a position to supply a monosynaptic drive for lid closure, and the adjacent reticular formation can supply a disynaptic drive. These findings indicate that the assignment of the R₁ and R₂ components of the blink reflex to different parts of the trigeminal sensory complex cannot be exclusively based on subdivision connectional relationships with facial motoneurons. The characteristics of the R₂ component may be due, instead, to other circuit properties.

The effects of unintentional drowsiness on the velocity of eyelid movements during spontaneous blinks

OBJECTIVE

Unintentional drowsiness, when we should be alert, as for example when driving a vehicle, can be very dangerous. In this investigation we examined the effects of unintentional drowsiness on the relative velocities of eyelid closing and reopening movements during spontaneous blinks.

APPROACH

Twenty-four young adults volunteered to take part in this experiment, and 18 were finally accepted. They performed a 15 min visual reaction-time test at the same time of day and under the same environmental conditions with and without overnight sleep deprivation, one week apart. Their eyelid movements during blinks were monitored by a system of infrared reflectance blepharometry during each test.

MAIN RESULTS

Very close relationships between the amplitude and maximum velocity of eyelid closing and reopening movements were confirmed. Frequency histograms of amplitude-velocity ratios (AVRs) for eyelid closing and reopening movements showed significant differences between alert and drowsy conditions. With drowsiness, eyelid movements became slower and AVRs increased for many but not all blinks. We also described a time-on-task effect on the relative velocities of eyelid movements which was more apparent in the drowsy condition. Eyelid movements became progressively slower during the first half of the test. This was presumably due to a short-lived alerting effect of starting the test.

SIGNIFICANCE

The relative velocity of eyelid closing and reopening movements during spontaneous blinks decreases with unintentional drowsiness but is sensitive to the brief alerting stimulus of starting a reaction-time test.

Overground Walking Decreases Alpha Activity and Entrains Eye Movements in Humans

Experiments in animal models have shown that running increases neuronal activity in early visual areas in light as well as in darkness. This suggests that visual processing is influenced by locomotion independent of visual input. Combining mobile electroencephalography, motion- and eye-tracking, we investigated the influence of overground free walking on cortical alpha activity (~10 Hz) and eye movements in healthy humans. Alpha activity has been considered a valuable marker of inhibition of sensory processing and shown to negatively correlate with neuronal firing rates. We found that walking led to a decrease in alpha activity over occipital cortex compared to standing. This decrease was present during walking in darkness as well as during light. Importantly, eye movements could not explain the change in alpha activity. Nevertheless, we found that walking and eye related movements were linked. While the blink rate increased with increasing walking speed independent of light or darkness, saccade rate was only significantly linked to walking speed in the light. Pupil size, on the other hand, was larger during darkness than during light, but only showed a modulation by walking in darkness. Analyzing the effect of walking with respect to the stride cycle, we further found that blinks and saccades preferentially occurred during the double support phase of walking. Alpha power, as shown previously, was lower during the swing phase than during the double support phase. We however could exclude the possibility that the alpha modulation was introduced by a walking movement induced change in electrode impedance. Overall, our work indicates that the human visual system is influenced by the current locomotion state of the body. This influence affects eye movement pattern as well as neuronal activity in sensory areas and might form part of an implicit strategy to optimally extract sensory information during locomotion.

Imaging and anatomical parameters of the lacrimal punctum and vertical canaliculus using optical coherence tomography

Purpose: The anatomical parameters of normal lacrimal puncta and vertical canaliculus using optical coherence tomography (OCT) and the OCT imaging features of punctal lesions were analyzed to provide a basis for clinical diagnosis and treatment. Methods: From June to September 2019, 40 volunteers (80 eyes) from Tongji Hospital were enrolled. The external punctal diameter (ELP) was measured using slit-lamp microscopy and OCT. The internal lacrimal punctal diameter (ILP) at 100 μm, vertical canalicular length (VCL), and tear meniscus depth were measured by OCT with open eyes. Twenty-eight volunteers (56 eyes) underwent the same examinations with their eyes closed. The OCT imaging features of 26 patients (27 eyes) with lacrimal lesions were examined. Results: The ELP of the right and left healthy eyes under slit-lamp microscopy were 564.40 and 555.40 µm respectively. Under OCT, the ELP, ILP, and VCL of the right and left eyes were 628.20 um and 616.85 µm, 343.40 µm and 346.95 µm, 731.95 um and 709.20 µm respectively. The ELP was larger when measured by OCT than slit-lamp microscopy (p<0.05). Twenty-eight volunteers (56 eyes) had measurements taken under different conditions. The ELP, ILP, and VCL of the open and closed right eyes were 667.54 and 567.21 µm, 369.18 and 303.18 µm, 715.00 and 417.14 µm, respectively. The ELP, ILP, and VCL of the open and closed left eyes were 655.86 um and 551.68 µm, 369.25 um and 313.54 µm, 719.96 um and 433.89 µm respectively. The anatomical parameters of the open eyes were greater than those of the closed eyes (p<0.05). Thus, we identified the imaging features of lacrimal stenosis, punctal obstruction, punctal tear, lacrimal atresia, and lacrimal mass using OCT. Conclusions: OCT can be used to measure the anatomical parameters of lacrimal puncta and vertical canaliculus in vivo. In addition, OCT can detect punctal lesions in vivo and provide an objective basis for the clinical diagnosis and treatment of punctal lesions.

T-pattern analysis and spike train dissimilarity for the analysis of structure in blinking behavior

Spontaneous eye-blinks are a ubiquitous behavior. However, blink timing is not random, nor does it always follow physiological demands. Research rather suggests that blink timing, and thus the structure of blinking behavior, is influenced by cognitive processes, such as attention. Since attention is regarded a necessary precursor of media use phenomena, the present study investigates the relation between the structure of blinking behavior and the media use phenomenon of spatial presence. To this end, spontaneous eye-blinks have been observed in an experiment during the reception of a video story. The methods of T-pattern analysis, ISI distance, and IBI variability have been used to quantify stimulus-dependent blink structure, which has then been related to self-reports of spatial presence experiences. While the T-pattern analysis and ISI distance showed converging results for behavior structure, a hypothesized relation between more stimulus-dependent blink structure and stronger presence experiences was not found. On the contrary, blink data suggested a difference in attention allocation, whereas self-report data indicated no difference in presence experiences. This demonstrates that beyond self-report and the analysis of event frequencies, the analysis of behavior structure offers insights into behavior synchronization between participants, allowing for new inferences on internal processing of media stimuli.

Intra-subject consistency of spontaneous eye blink rate in young women across the menstrual cycle

The spontaneous eye blink rate (EBR) has been linked to different cognitive processes and neurobiological factors. It has also been proposed as a putative index for striatal dopaminergic function. While estradiol is well-known to increase dopamine levels through multiple mechanisms, no study up to date has investigated whether the EBR changes across the menstrual cycle. This question is imperative however, as women have sometimes been excluded from studies using the EBR due to potential effects of their hormonal profile. Fifty-four women were tested for spontaneous EBR at rest in three different phases of their menstrual cycle: during menses (low progesterone and estradiol), in the pre-ovulatory phase (when estradiol levels peak and progesterone is still low), and during the luteal phase (high progesterone and estradiol). No significant differences were observed across the menstrual cycle and Bayes factors show strong support for the null hypothesis. Instead, we observed high intra-individual consistency of the EBR in our female sample. Accordingly, we strongly encourage including female participants in EBR studies, regardless of their cycle phase.

The influence of a lipid reservoir on the tear film formation

We present a mathematical model to study the influence of a lipid reservoir, seen experimentally, at the lid margin on the formation and relaxation of the tear film during a partial blink. Applying the lubrication limit, we derive two coupled non-linear partial differential equations characterizing the evolution of the aqueous tear fluid and the covering insoluble lipid concentration. Departing from prior works, we explore a new set of boundary conditions (BCs) enforcing hypothesized lipid concentration dynamics at the lid margins. Using both numerical and analytical approaches, we find that the lipid-focused BCs strongly impact tear film formation and thinning rates. Specifically, during the upstroke of the eyelid, we find specifying the lipid concentration at the lid margin accelerates thinning. Parameter regimes that cause tear film formation success or failure are identified. More importantly, this work expands our understanding of the consequences of lipid dynamics near the lid margins for tear film formation.

Drowsiness or mind-wandering? Fluctuations in ocular parameters during attentional lapses

Two independent lines of evidence suggest that drowsiness and mind-wandering share common neurocognitive processes indexed by ocular parameters (e.g., eyeblink frequency and pupil dynamics). Mind-wandering and drowsiness frequently co-occur, however, such that it remains unclear whether observed oculometric variations are related to mind-wandering, drowsiness, or a mix of both. To address this issue, we assessed fluctuations in mind-wandering and sleepiness during a sustained attention task while ocular parameters were recorded. Results showed that oculometric variations during mind-wandering were fully explained by increased sleepiness. However, mind-wandering and sleepiness had additive deleterious effects on performance that were not fully explained by ocular parameters. These findings suggest that oculometric variations during task performance reflect increased drowsiness rather than processes specifically involved in mind-wandering, and that the neurocognitive processes indexed by oculometric parameters (e.g., regulatory processes of the locus coeruleus norepinephrine system) do not fully explain how mind-wandering and sleepiness cause attentional lapses.