Ocular Metrics Research Articles

Correlation Between Physiological and Performance-Based Metrics to Estimate Pilots' Cognitive Workload.

This paper discusses the utilization of pilots' physiological indications such as electroencephalographic (EEG) signals, ocular parameters, and pilot performance-based quantitative metrics to estimate cognitive workload. The study aims to derive a non-invasive technique to estimate pilot's cognitive workload and study their correlation with standard physiological parameters. Initially, we conducted a set of user trials using well-established psychometric tests for evaluating the effectiveness of pupil and gaze-based ocular metrics for estimating cognitive workload at different levels of task difficulty and lighting conditions. Later, we conducted user trials with the NALSim flight simulator using a business class Learjet aircraft model. We analyzed participants' ocular parameters, power levels of different EEG frequency bands, and flight parameters for estimating variations in cognitive workload. Results indicate that introduction of secondary task increases pilot's cognitive workload significantly. The beta frequency band of EEG, nearest neighborhood index specifying distribution of gaze fixation, L1 Norm of power spectral density of pupil diameter, and the duty cycle metric indicated variations in cognitive workload.

Driver monitoring systems (DMS): The future of impaired driving management?

Objective Driver monitoring systems (DMS) are the next generation of vehicle safety technology. Broadly, these refer to the embedded, aftermarket wearable or vehicle-mounted devices that collect observable information about the operator to make real-time assessment of their capacity to perform the driving task. Integrating biobehavioral monitoring (primarily ocular metrics) with driving performance assessments, these systems function to infer driver state in real time to identify operator conditions that negatively affect driving (such as fatigue, inattention, or distraction). Method We review available methods used to infer driver state, as referenced against accepted models for optimal performance. Modeling our observations on deviation from predetermined performance thresholds used to trigger graded safety alerts, we suggest that many psychoactive substances produce alterations to biobehavioral processes including attentional and motor control, which affect performance indices in a manner already arguably captured by these technologies. Results Using these existing frameworks, there is considerable potential to similarly catalogue the effect of many common intoxicants known to negatively affect driving ability. This will provide safety-relevant and practical biological models for the development of next-generation multimodal DMS that integrate ocular and physiological variables sensitive to the effects of common and emergent psychoactive substances. Conclusion These devices have tangible potential application across all areas of transportation, including aviation, rail, and all commercial and private vehicle systems.

Risk Factors for Onset or Progression of Posterior Vitreous Detachment at the Vitreomacular Interface after Cataract Surgery

To study the incidence and risk factors for onset or progression of posterior vitreous detachment (PVD) at the vitreomacular interface (VMI) after cataract surgery. Retrospective case series. Patients with a history of phacoemulsification from April 2018 through April 2019 at the Keye Eye Center, Seoul, Korea, and postoperative monitoring for more than 2 months. Cox proportional hazard ratios for the onset or development of PVD after cataract surgery in the presence of selected risk factors and demographic data were calculated. To evaluate the ocular risk factors, various ocular metrics, including spherical equivalent (SE), axial length (AL), anterior chamber depth, lens thickness, central subfield thickness, PVD status at macula and optic nerve head (ONH), peripapillary retinal nerve fiber layer thickness, and ONH parameters from OCT scans, were used for the analysis. Onset or development of PVD at the VMI. Among 988 eyes without PVD at baseline, 174 eyes (17.6%) showed changes in the VMI. Univariate analysis showed that age, SE, AL, PVD status at macula and ONH, and average and vertical cup-to-disc ratios (CDRs) were associated significantly with PVD onset or development (P= 0.046, P= 0.004, P= 0.040, P < 0.001, P < 0.001, P= 0.008, and P= 0.042, respectively). In a multivariate analysis, PVD status at the macula and ONH and smaller CDR were associated with PVD onset or progression after cataract surgery after adjustment for age, SE, and AL (P < 0.001, P < 0.001, and P= 0.005, respectively). The risk of PVD onset or progression was dependent on PVD status and the CDR detected on OCT scans, not on age or AL, in a large patient cohort. Patients who show risk factors on OCT should be monitored carefully during the postoperative period.

Cognitive load estimation using ocular parameters in automotive

In automotive, usage of electronic devices increased visual inattention of drivers while driving and might lead to accidents. It is often challenging to detect if a driver experienced a change in cognitive state requiring new technology that can best estimate driver's cognitive load. In this paper, we investigated the efficacy of various ocular parameters to estimate cognitive load and detect cognitive state of driver. We derived gaze and pupil-based metrics and evaluated their efficacy in classifying different levels of cognitive states while performing psychometric tests in varying light conditions. We validated the performance of our metrics in simulation as well as in-car environments. We compared the accuracy (from confusion matrix) of detecting cognitive state while performing secondary task using our proposed metrics and Machine Learning models. It was found that a Neural Network model combining multiple ocular metrics showed better accuracy (75%) than individual ocular metrics. Finally, we demonstrated the potential of our system to alert drivers in real-time under critical distractions.

A Novel and Simple Method to Assess Corneal Biomechanics Using Schiotz Tonometer

Background: The present study introduces a novel method to evaluate corneal biomechanics, which has a key role in diagnosing keratoconus (KC) or keratectasia (KE). Methods: In this multicentre, prospective, single-blind study, patients with myopia, cataracts, or KC underwent corneal biomechanics evaluation with a Schiotz tonometer, before and after corneal crosslinking (CXL) or Femtosecond assisted laser in situ keratomileusis (FS-LASIK). The corneal biomechanics metric (Mulee factor, MF) was calculated from the data obtained with the tonometer. Clinical significance was verified by analysis of the correlation of MF and ocular morphology metrics and efficiency of MF in predicting the occurrence of KC or KE. Findings: A negative relation was found between the MF and Young’s modulus (P<0·001) and MF and maximal stress (P<0·001) in an in vitro study on rabbit eyeballs. MF in normal eyes (myopia and cataract eyes) was 2·890·43. MF before FS-LASIK was 2·940·35, increasing to 3·710·42 one month after FS-LASIK (P<0·001). In the normal population, pre-operative MF was negatively correlated with age (P<0·001), positively correlated with central corneal thickness (P=0·03), but not related to anterior chamber depth, ocular axis length, intraocular pressure, cornea diameter, and cornea curvature. MF was 4·090·56, decreasing to 2·140·55 one month after CXL. MF was 3·360·51 in eyes with forme fruste keratoconus (FFKC). There were 3, 6, and 10 cases of KC or KE after FS-LASIK, CXL, or FFKC, respectively. The cut-off points for predicting KC or KE with MFs were 4·67, 2·67, and 3·5 in patients with FS-LASIK, KC, and FFKC (P<0·01, P<0·01, and P<0·01, respectively). Interpretation: The MF can sensitively reflect corneal biomechanics and is not influenced by ocular metrics. The MF predicts KC and KE with high specificity and sensitivity. Funding Statement: This study was supported by the Natural Science Foundation of Shandong Province (2009GQ10002037). Declaration of Interests: There are no conflicts of interest to declare. Ethics Approval Statement: Animals used in this study were treated in accordance with Shandong Provincial Hospital affiliated to Shandong University Animal Experimentation Ethic Committee (AEEC) guidelines, and were approved by the AEEC.

Development and Characterization of a Benchtop Corneal Puncture Injury Model

During recent military operations, eye-related injuries have risen in frequency due to increased use of explosive weaponry which often result in corneal puncture injuries. These have one of the poorest visual outcomes for wounded soldiers, often resulting in blindness due to the large variations in injury shape, size, and severity. As a result, improved therapeutics are needed which can stabilize the injury site and promote wound healing. Unfortunately, current corneal puncture injury models are not capable of producing irregularly shaped, large, high-speed injuries as seen on the battlefield, making relevant therapeutic development challenging. Here, we present a benchtop corneal puncture injury model for use with enucleated eyes that utilizes a high-speed solenoid device suitable for creating military-relevant injuries. We first established system baselines and ocular performance metrics, standardizing the different aspects of the benchtop model to ensure consistent results and properly account for tissue variability. The benchtop model was evaluated with corneal puncture injury objects up to 4.2 mm in diameter which generated intraocular pressure levels exceeding 1500 mmHg. Overall, the created benchtop model provides an initial platform for better characterizing corneal puncture injuries as seen in a military relevant clinical setting and a realistic approach for assessing potential therapeutics.

Eye gaze patterns reveal how reasoning skills improve with experience

Reasoning, our ability to solve novel problems, has been shown to improve as a result of learning experiences. However, the underlying mechanisms of change in this high-level cognitive ability are unclear. We hypothesized that possible mechanisms include improvements in the encoding, maintenance, and/or integration of relations among mental representations – i.e., relational thinking. Here, we developed several eye gaze metrics to pinpoint learning mechanisms that underpin improved reasoning performance. We collected behavioral and eyetracking data from young adults who participated in a Law School Admission Test preparation course involving word-based reasoning problems or reading comprehension. The Reasoning group improved more than the Comprehension group on a composite measure of four visuospatial reasoning assessments. Both groups improved similarly on an eyetracking paradigm involving transitive inference problems, exhibiting faster response times while maintaining high accuracy levels; nevertheless, the Reasoning group exhibited a larger change than the Comprehension group on an ocular metric of relational thinking. Across the full sample, individual differences in response time reductions were associated with increased efficiency of relational thinking. Accounting for changes in visual search and a more specific measure of relational integration improved the prediction accuracy of the model, but changes in these two processes alone did not adequately explain behavioral improvements. These findings provide evidence of transfer of learning across different kinds of reasoning problems after completing a brief but intensive course. More broadly, the high temporal precision and rich derivable parameters of eyetracking make it a powerful approach for probing learning mechanisms.

Assessment of Ocular and Physiological Metrics to Discriminate Flight Phases in Real Light Aircraft.

The purpose of the present study was to find psychophysiological proxies that are straightforward to use and could be implemented in actual flight conditions to accurately discriminate pilots' workload levels. Piloting an aircraft is a complex activity where cognitive limitations may jeopardize flight safety. There is a need to implement solutions to monitor pilots' workload level to improve flight safety. There has been recent interest in combining psychophysiological measurements. Most of these studies were conducted in flight simulators at the group level, limiting the interpretation of the results. We conducted an experiment with 11 pilots performing two standard traffic patterns in a light aircraft. Five metrics were derived from their ocular and cardiac activities and were evaluated through three flight phases: takeoff, downwind, and landing. Statistical analyses showed that the saccadic rate was the most efficient metric to distinguish between the three flight phases. In addition, a classifier trained on the ocular data collected from the first run predicted the flight phase within a second run with an accuracy of 75%. No gain in the classifier accuracy has been found by combining cardiac and ocular metrics. Ocular-based metrics may be more suitable than cardiac ones to provide relevant information on pilots' flying activity in operational settings. Electrocardiographic and eye-tracking devices could be implemented in future cockpits as additional flight data for accident analysis, an objective pilot's state evaluation for training, and proxies for human-machine interactions to improve flight safety.

Relationship Between Neurocognitive Testing and Saccadic Eye Movements in Symptom Free Division I Athletes

Saccadic eye movements are produced from several frontal and parietal cortical regions of the brain that also aid in the execution of cognitive functions. However, no known research has examined the relationship between a sport-like antisaccade task and standard neurocognitive exams. PURPOSE: To evaluate the relationship between the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) cognitive domains and a sport-like antisaccade task (SLT) of Division I athletes on symptom free-day of post- sport like concussion. METHODS: 10 concussed individuals (8 males; 2 females; age: 20 ± 2 years) were assessed on the ImPACT test and the SLT on a symptom free day post- sport related concussion. A monocular eye tracker (240Hz, Argus Science) synced with the Vicon Motion Capture System (Vicon Motion Ltd., Version 1.85, Oxford, England) was employed to track raw ocular coordinates and further analyzed to obtain resultant distance (RD), mean horizontal velocity (MHV), and prosaccade errors (PE) during the athlete’s participation in the SLT. ImPACT variables included verbal and visual memory composite, visual motor speed, reaction time composite (RT), and impulse control. All eye variables were run through a custom MatLab code (MATLAB 2017, Mathworks, Inc., Matick, MA). Spearman rho correlations were used to assess the relationship between ImPACT variables and ocular metrics. RESULTS: Significant negative moderate relationships (r = -0.70, p = 0.02) between MHV (5.78 ± 1.28 pixels/second) and reaction time composite score (0.57 ± 0.07) were observed. Similarly, there was a significant negative moderate relationship (r= -0.65, p = 0.03) between RD (2.73 ± 1.03 pixels) and Impulse control composite score (6.4 ± 3.75). No other significant relationships were noted. CONCLUSION: These significant relationships suggest that as eye velocities increase, RT decreases which is possibly due to a decrease in accuracy on overall cognitive efficiency. As impulse control decreases, the eye movement resultant distances are minimal. This may be due to more cognitive errors that lead to an inability to properly control antisaccadic eye movements. Due to the relationships exhibited between the ImPACT and SLT, it can be suggested that antisaccade eye movements contain a neurocognitive component.

Driver’s emotional state and detection of vulnerable road users: Towards a better understanding of how emotions affect drivers’ perception using cardiac and ocular metrics

Traditionally, anger has been considered to have a detrimental effect on driving. However, recent studies suggest that this statement should be qualified, especially where vulnerable road user detection is concerned. One primary factor which may determine anger’s effect on a driver’s attention is its intensity. In the present study, different intensities of anger were elicited via film clips, then performances in vulnerable road user detection (i.e., of cyclists) were assessed while participants drove a car in a simulated environment. Cardiac and ocular measurements and self-reported data were used in order to accurately assess emotional state and attention management throughout the experiment. Results suggested that participants resorted to reappraisal strategies when they were exposed to the emotional film clips. This phenomenon did not directly affect cyclist detection performances, but evidence of different visual scanning strategies between groups emerged. The contribution of cardiac and ocular measurements to emotional assessment and the advantages of appraisal approaches of emotion were also discussed.

Real-Time Assessment of Operator State in Air Traffic Controllers Using Ocular Metrics

This study examined the utility of continuous operator state monitoring in predicting air traffic control officer (ATCO) workload and fatigue. Participants (N=8) were observed in live operational air traffic control environments for 60-minute periods. ATCO state was assessed using a real-time, computer vision-based system which tracked operator gaze and pupil diameter. Workload and fatigue were also assessed via the adapted Bedford Workload Scale and Samn-Perelli Fatigue Scale, respectively. Standard deviation of gaze was a significant predictor of both max and mean workload, showing a strong negative relationship with both subjective measures. Pupil diameter showed a significant positive relationship with operator fatigue. Our findings demonstrate the utility of continuous ocular metrics of workload and fatigue in operational environments.

Exploration of peripapillary vessel density in highly myopic eyes with peripapillary intrachoroidal cavitation and its relationship with ocular parameters using optical coherence tomography angiography.

Identifying changes of peripapillary vessel density in highly myopic eyes with peripapillary intrachoroidal cavitation by optical coherence tomography angiography. To investigate peripapillary vessel density and its relationship with other ocular parameters in highly myopic eyes with peripapillary intrachoroidal cavitation. Hospital-based, cross-sectional study. Thirty-five highly myopic eyes with peripapillary intrachoroidal cavitation, 46 highly myopic eyes without peripapillary intrachoroidal cavitation and 36 normal eyes were included in this study. All participants underwent optical coherence tomography angiography to image the retinal vasculature in the peripapillary areas, including the radial peripapillary capillaries and optic nerve head layer. Correlations between vessel density and ocular metrics were analysed. Peripapillary vessel density. In highly myopic eyes, vessel density was significantly lower in eyes with peripapillary intrachoroidal cavitation than in those without in peripapillary (P = 0.014, P = 0.037), inferotemporal (P < 0.001, P < 0.001) and superotemporal (P = 0.014, P = 0.009) areas. In the radial peripapillary capillaries layer, vessel density was negatively correlated with peripapillary atrophy area (P = 0.012) and myopic maculopathy (P = 0.002), and in the optic nerve head layer, it was negatively associated with a diagnosis of peripapillary intrachoroidal cavitation (P = 0.012) and myopic maculopathy (P < 0.001). In addition, it was positively correlated with retinal nerve fibre layer thickness in both layers (P < 0.001). Highly myopic eyes with peripapillary intrachoroidal cavitation had lower peripapillary vessel densities, especially in the temporal area, than those without.

Air traffic control: Ocular metrics reflect cognitive complexity

The objective of the study was to evaluate effects of complexity on cognitive workload in a simulated air traffic control conflict detection task by means of eye movements recording. We manipulated two complexity factors, convergence angle and aircrafts minimum distance at closest approach, in a multidimensional workload assessment method based on psychophysiological, performance, and subjective measures. Conflict trials resulted more complex and time-consuming than no conflicts, requiring more frequent fixations and saccades. Moreover, large saccades showed reduced burst power with higher task complexity. A motion-based and a ratio-based strategy were suggested for conflicts and no conflicts on the basis of ocular metrics analysis: aircrafts differential speed and distance to convergence point at trial start were considered determinant for strategy adoption. Relevance to industryEye metrics measurement for online workload assessment enhances better identification of workload-inducing scenarios and adopted strategy for traffic management. System design, as well as air traffic control operators training programs, might benefit from on line workload measurement.

The utility of automated measures of ocular metrics for detecting driver drowsiness during extended wakefulness

Slowed eyelid closure coupled with increased duration and frequency of closure is associated with drowsiness. This study assessed the utility of two devices for automated measurement of slow eyelid closure in a standard poor performance condition (alcohol) and following 12-h sleep deprivation. Twenty-two healthy participants (mean age=20.8 (SD 1.9) years) with no history of sleep disorders participated in the study. Participants underwent one baseline and one counterbalanced session each over two weeks; one 24-hour period of sleep deprivation, and one daytime session during which alcohol was consumed after a normal night of sleep. Participants completed a test battery consisting of a 30-min simulated driving task, a 10-min Psychomotor Vigilance Task (PVT) and the Karolinska Sleepiness Scale (KSS) each in two baseline sessions, and in two randomised, counterbalanced experimental sessions; following sleep deprivation and following alcohol consumption. Eyelid closure was measured during both tasks using two automated devices (Copilot and Optalert™). There was an increase in the proportion of time with eyelids closed and the Johns Drowsiness Score (incorporating relative velocity of eyelid movements) following sleep deprivation using Optalert (p<0.05 for both). These measures correlated significantly with crashes, PVT lapses and subjective sleepiness (r-values 0.46–0.69, p<0.05). No difference between the two sessions for PERCLOS recorded during the PVT or the driving task as measured by the Copilot. The duration of eyelid closure predicted frequent lapses following sleep deprivation (which were equivalent to the average lapses at a blood alcohol concentration of 0.05% – area under curve for ROC curve 0.87, p<0.01). The duration of time with slow eyelid closure, assessed by the automated devices, increased following sleep deprivation and was associated with deterioration in psychomotor performance and subjective sleepiness. Comprehensive algorithms inclusive of ocular parameters may be a better indicator of performance impairment following sleep loss.

Discovery and functional annotation of SIX6 variants in primary open-angle glaucoma.

Glaucoma is a leading cause of blindness worldwide. Primary open-angle glaucoma (POAG) is the most common subtype and is a complex trait with multigenic inheritance. Genome-wide association studies have previously identified a significant association between POAG and the SIX6 locus (rs10483727, odds ratio (OR) = 1.32, p = 3.87×10−11). SIX6 plays a role in ocular development and has been associated with the morphology of the optic nerve. We sequenced the SIX6 coding and regulatory regions in 262 POAG cases and 256 controls and identified six nonsynonymous coding variants, including five rare and one common variant, Asn141His (rs33912345), which was associated significantly with POAG (OR = 1.27, p = 4.2×10−10) in the NEIGHBOR/GLAUGEN datasets. These variants were tested in an in vivo Danio rerio (zebrafish) complementation assay to evaluate ocular metrics such as eye size and optic nerve structure. Five variants, found primarily in POAG cases, were hypomorphic or null, while the sixth variant, found only in controls, was benign. One variant in the SIX6 enhancer increased expression of SIX6 and disrupted its regulation. Finally, to our knowledge for the first time, we have identified a clinical feature in POAG patients that appears to be dependent upon SIX6 genotype: patients who are homozygous for the SIX6 risk allele (His141) have a statistically thinner retinal nerve fiber layer than patients homozygous for the SIX6 non-risk allele (Asn141). Our results, in combination with previous SIX6 work, lead us to hypothesize that SIX6 risk variants disrupt the development of the neural retina, leading to a reduced number of retinal ganglion cells, thereby increasing the risk of glaucoma-associated vision loss.

Assessment of Drowsiness Based on Ocular Parameters Detected by Infrared Reflectance Oculography

Numerous ocular parameters have been proposed as reliable physiological markers of drowsiness. A device that measures many of these parameters and then combines them into a single metric (the Johns Drowsiness Scale [JDS]) is being used commercially to assess drowsiness in professional drivers. Here, we examine how these parameters reflect changes in drowsiness, and how they relate to objective and subjective indices of the drowsy state in a controlled laboratory setting. A within subject prospective study. 29 healthy adults (18 males; mean age 23.3 ± 4.6 years; range 18-34 years). N/A. Over the course of a 30-h extended wake vigil under constant routine (CR) conditions, participants were monitored using infrared reflectance oculography (Optalert) and completed bi-hourly neurobehavioral tests, including the Karolinska Sleepiness Scale (KSS) and Psychomotor Vigilance Task (PVT). Ocular-defined increases in drowsiness were evident with extended time awake and during the biological night for all ocular parameters; JDS being the most sensitive marker of drowsiness induced by sleep regulatory processes (p < 0.0001). In addition, the associations between JDS in the preceding 10-min period and subsequent PVT lapses and KSS were stronger (AUC 0.74/0.80, respectively) than any other ocular metric, such that PVT lapses, mean response time (RT), and KSS increased in a dose-response manner as a function of prior JDS score (p < 0.0001). Ocular parameters captured by infrared reflectance oculography detected fluctuations in drowsiness due to time awake and during the biological night. The JDS outcome was the strongest predictor of drowsiness among those tested, and showed a clear association to objective and subjective measures of drowsiness. Our findings indicate this real-time objective drowsiness monitoring system is an effective tool for monitoring changes in alertness and performance along the alert-drowsy continuum in a controlled laboratory setting.