Effect of Age, Sex, Stimulus Intensity, and Eccentricity on Saccadic Reaction Time in Eye Movement Perimetry

Effect of ethnic diversity on the saccadic reaction time among healthy Indian and Dutch adults

Eye movement perimetry (EMP) expresses the decline in visual field (VF) responsiveness based on the deviation in saccadic reaction times (SRTs) from their expected age-similar responses (normative database). Since ethnic dissimilarities tend to affect saccade parameters, we evaluated the effect of such a factor on SRT and its interaction with age, stimulus eccentricity, and intensity. 149 healthy adults, spread into five age groups, drawn from Indian and Dutch ethnicities underwent a customized EMP protocol integrated with a saccade task from which the SRTs to 'seen' visual stimuli were computed. The EMP test had a total of 54 coordinates (five stimulus eccentricities) tested using Goldmann size III visual stimuli presented at four stimulus intensity (SI) levels against a constant background. Considering SRT as a dependent variable, a Generalized Linear Mixed Model analysis was conducted that revealed a statistically significant (p < 0.001) influence of ethnicity and interaction between the tested factors (ethnicity × age × stimulus eccentricity × intensity). However, during the post hoc analysis, out of the 100 possible pair-wise comparisons, only 6% (minor proportion) of the estimates showed statistical significance. Hence, the ethnic-specific differences need not be accounted for while implementing EMP in a diverse set of populations instead a collective database might serve the purpose.

Automated Eye Tracking Enables Saccade Performance Evaluation of Patients with Concussion History

SIGNIFICANCE

Automated eye tracking could be used to evaluate saccade performance of patients with concussion history, providing quantitative insights about the degree of oculomotor impairment and potential vision rehabilitation strategies for this patient population.

PURPOSE

To evaluate the saccade performance of patients with concussion history based on automated eye-tracking test results.

METHODS

We conducted a retrospective study of patients with concussion history, primarily from sports participation, who underwent oculomotor testing based on an eye-tracking technology at the Duke Eye Center vision rehabilitation clinic between June 30, 2017, and January 10, 2022. Patients' saccade test results were reviewed, including saccade fixation and saccade speed/accuracy ratio. The outcomes were compared with age-matched normative population data derived from healthy individuals. Multiple linear regression analyses were performed to identify factors associated with saccade performance among patients with concussion history.

RESULTS

On hundred fifteen patients with concussion history were included in the study. Patients with concussion, on average, had fewer fixations on self-paced horizontal and vertical saccade tests and lower horizontal and vertical saccade speed/accuracy ratios compared with normative ranges. Among patients with concussion history, multiple linear regression analyses showed that older age was associated with fewer fixations on horizontal and vertical saccade tests, whereas male sex was associated with more fixations on horizontal and vertical saccade tests (all P < .01). In addition, older age was associated with lower horizontal saccade speed/accuracy ratio, after adjusting for sex, number of concussion(s), and time from most recent concussion to oculomotor testing ( P < .001).

CONCLUSIONS

Patients with concussion history had lower saccade performance based on eye tracking compared with healthy individuals. We additionally identified risk factors for lower saccade performance among patients with concussion history. These findings support the use of saccade test results as biomarkers for concussion and have implications for post-concussion rehabilitation strategies.

Estimating the differences between inter-operator contrast enhancement in cerebral CT angiography

BACKGROUND

Computed tomography (CT) angiography (CTA) is a non-invasive imaging method used to detect arteries and examine various brain diseases. When CTA is performed for follow-up or postoperative evaluation, reproducibility of vessel delineation is required. A reproducible and stable contrast enhancement can be achieved by manipulating the factors affecting it. Previous studies have investigated several factors that alter the contrast enhancement of arteries. However, no reports establishing the effect of different operators on contrast enhancement exist.

PURPOSE

To assess the differences between inter-operator arterial contrast enhancement in cerebral CTA using Bayesian statistical modeling.

METHODS

Image data were obtained using a multistage sampling method from the cerebral CTA scans of patients who underwent the process between January 2015 and December 2018. Several Bayesian statistical models were developed, and the objective variable was the mean CT number of the bilateral internal carotid arteries after contrast enhancement. The explanatory variables were sex, age, fractional dose (FD), and the operator's information. The posterior distributions of the parameters were computed via Bayesian inference using the Markov chain Monte Carlo (MCMC) method, with the Hamiltonian Monte Carlo method employed as the algorithm. The posterior predictive distributions were computed using the posterior distributions of the parameters. Finally, the differences between inter-operator arterial contrast enhancement on the CT number in cerebral CTA were estimated.

RESULTS

The posterior distributions showed that all parameters representing the difference between operators included zero at the 95% credible intervals (CIs). The maximum mean difference between inter-operator CT number in the posterior predictive distribution was only 12.59 Hounsfield units (HUs).

CONCLUSIONS

The Bayesian statistical modeling results suggest that contrast enhancement of cerebral CTA examination between operator-to-operator differences in postcontrast CT number was small compared to those within-operator differences resulting from factors not considered in the model.

The Effect of Stimulus Contrast and Spatial Position on Saccadic Eye Movement Parameters

(1) Background: Saccadic eye movements are rapid eye movements aimed to position the object image on the central retina, ensuring high-resolution data sampling across the visual field. Although saccadic eye movements are studied extensively, different experimental settings applied across different studies have left an open question of whether and how stimulus parameters can affect the saccadic performance. The current study aims to explore the effect of stimulus contrast and spatial position on saccadic eye movement latency, peak velocity and accuracy measurements. (2) Methods: Saccadic eye movement targets of different contrast levels were presented at four different spatial positions. The eye movements were recorded with a Tobii Pro Fusion video-oculograph (250 Hz). (3) Results: The results demonstrate a significant effect of stimulus spatial position on the latency and peak velocity measurements at a medium grey background, 30 cd/m2 (negative and positive stimulus polarity), light grey background, 90 cd/m2 (negative polarity), and black background, 3 cd/m2 (positive polarity). A significant effect of the stimulus spatial position was observed on the accuracy measurements when the saccadic eye movement stimuli were presented on a medium grey background (negative polarity) and on a black background. No significant effect of stimulus contrast was observed on the peak velocity measurements under all conditions. A significant stimulus contrast effect on latency and accuracy was observed only on a light grey background. (4) Conclusions: The best saccadic eye movement performance (lowest latency, highest peak velocity and accuracy measurements) can be observed when the saccades are oriented to the right and left from the central fixation point. Furthermore, when presenting the stimulus on a light grey background, a very low contrast stimuli should be considered carefully.

Stimulus contrast, pursuit mode, and age strongly influence tracking performance on a continuous visual tracking task

Human observers tend to naturally track moving stimuli. This tendency may be exploited towards an intuitive means of screening visual function as an impairment induced reduction in stimulus visibility will decrease tracking performance. Yet, to be able to detect subtle impairments, stimulus contrast is critical. If too high, the decrease in performance may remain undetected. Therefore, for this approach to become reliable and sensitive, we need a detailed understanding of how age, stimulus contrast, and the type of stimulus movement affect continuous tracking performance. To do so, we evaluated how well twenty younger and twenty older participants tracked a semi-randomly moving stimulus (Goldmann size III, 0.43 degrees of visual angle), presented at five contrast levels (5%-10%-20%-40%-80%). The stimulus could move smoothly only (smooth pursuit mode) or in alternation with displacements (saccadic pursuit mode). Additionally, we assessed static foveal and peripheral contrast thresholds. For all participants, tracking performance improved with increasing contrast in both pursuit modes. To reach threshold performance levels, older participants required about twice as much contrast (20% vs. 10% and 40% vs. 20% in smooth and saccadic modes respectively). Saccadic pursuit detection thresholds correlated significantly with static peripheral contrast thresholds (rho = 0.64). Smooth pursuit detection thresholds were uncorrelated with static foveal contrast thresholds (rho = 0.29). We conclude that continuous visual stimulus tracking is strongly affected by stimulus contrast, pursuit mode, and age. This provides essential insights that can be applied towards new and intuitive approaches of screening visual function.

Eye Movement Abnormalities in Glaucoma Patients: A Review

Glaucoma is a common condition that relies on careful clinical assessment to diagnose and determine disease progression. There is growing evidence that glaucoma is associated not only with loss of retinal ganglion cells but also with degeneration of cortical and subcortical brain structures associated with vision and eye movements. The effect of glaucoma pathophysiology on eye movements is not well understood. In this review, we examine the evidence surrounding altered eye movements in glaucoma patients compared to healthy controls, with a focus on quantitative eye tracking studies measuring saccades, fixation, and optokinetic nystagmus in a range of visual tasks. The evidence suggests that glaucoma patients have alterations in several eye movement domains. Patients exhibit longer saccade latencies, which worsen with increasing glaucoma severity. Other saccadic abnormalities include lower saccade amplitude and velocity, and difficulty inhibiting reflexive saccades. Fixation is pathologically altered in glaucoma with reduced stability. Optokinetic nystagmus measures have also been shown to be abnormal. Complex visual tasks (eg reading, driving, and navigating obstacles), integrate these eye movements and result in behavioral adaptations. The review concludes with a summary of the evidence and recommendations for future research in this emerging field.

Slowed Saccadic Reaction Times in Seemingly Normal Parts of Glaucomatous Visual Fields

Purpose: In eye movement perimetry, peripheral stimuli are confirmed by goal-directed eye movements toward the stimulus. The saccadic reaction time (SRT) is regarded as an index of visual field responsiveness, whereas in standard automated perimetry (SAP), the visual field sensitivity is tested. We investigated the relation between visual field sensitivity and responsiveness in corresponding locations of the visual field in healthy controls and in patients with mild, moderate and advanced glaucoma.

Materials and Methods: Thirty-four healthy control subjects and 42 glaucoma patients underwent a 54-point protocol in eye movement perimetry (EMP) and a 24-2 SITA standard protocol in a Humphrey Field Analyzer. The visual field points were stratified by total deviation sensitivity loss in SAP into 6 strata. A generalized linear mixed model was applied to determine the influence of the various factors.

Results: The generalized linear mixed model showed that the mean SRT increased with increasing glaucoma severity, from 479 ms in the control eyes to 678 ms in the eyes of patients with advanced glaucoma (p < 0.001). Mean SRTs significantly increased with increasing SAP sensitivity loss. Even at the locations where no sensitivity loss was detected by SAP (total deviation values greater or equal than 0 dB), we found lengthened SRTs in mild, moderate and advanced glaucoma compared to healthy controls (p < 0.05) and in moderate and advanced glaucoma compared to mild glaucoma (p < 0.05). At locations with total deviation values between 0 and −3 dB, −3 and −6 dB and −6 and −12 dB, we found similar differences.

Conclusions: The lengthened SRT in areas with normal retinal sensitivities in glaucomatous eyes, i.e., planning and execution of saccades to specific locations, precede altered sensory perception as assessed with SAP. Better understanding of altered sensory processing in glaucoma might allow earlier diagnosis of emerging glaucoma.

Comparison of Saccadic Eye Movements Among the High-tension Glaucoma, Primary Angle-closure Glaucoma, and Normal-tension Glaucoma

PRCIS

Saccadic eye movements were compared between high-tension glaucoma (HTG), normal-tension glaucoma (NTG), and primary angle-closure glaucoma (PACG). Saccades were differently affected between the subtypes of primary glaucoma.

AIM

The aim of the study was to compare saccadic eye movements in eyes with HTG, PACG, and NTG.

METHODS

Saccadic eye movements were recorded using the eye tracker Eyelink-1000 in 52 participants: 15 HTG, 14 PACG, 8 NTG, and 15 normal controls. All participants underwent a complete ophthalmic and visual field examination. Prosaccades were measured using the gap paradigm. Prosaccades were measured at 3 target eccentricities (5-, 7-, and 10-degree eccentricity). All prosaccade targets were projected outside the area of visual field defect. Saccade latency, average and peak velocity, and amplitude difference of the saccades were compared between glaucoma subtypes.

RESULTS

The mean±SD age was lesser in controls compared with glaucoma (P=0.02). The mean age in all the glaucoma subtypes was comparable (P=0.92). The average mean deviation in PACG (-16.66±6.69 dB) was worse (P=0.01) than in HTG (-11.56±6.08 dB) and NTG (-9.55±3.96 dB). The latencies were delayed, average and peak velocities were reduced, and saccades were hypometric in glaucoma compared with controls (P<0.01). Between subtypes, the differences in latency (P<0.01), peak velocity (P=0.02), and amplitude (P=0.02) were significant. Saccadic eye movements were significantly different in NTG compared with other glaucoma subtypes (post hoc analysis; latency (HTG vs. NTG; P<0.01, HTG vs. PACG; P=0.01), peak velocity (HTG vs. NTG; P=0.02) and amplitude difference (HTG vs. NTG; P=0.02).

CONCLUSIONS

Saccadic eye movement parameters were differently affected among the glaucoma subtypes. Saccadic parameters were more affected in NTG.

Saccadic reaction time in mirror image sectors across horizontal meridian in eye movement perimetry

In eye movement perimetry (EMP), the saccadic reaction time (SRT) to ‘seen’ visual stimuli are delayed in glaucoma. Evaluating SRT behaviour in hemi-field sectors could refine its clinical implication. The development phase included 60 controls retrospectively and for the test cohort in evaluation phase, another 30 healthy subjects and 30 glaucoma patients were recruited prospectively. The SRTs were used to calculate the normative limits within 5 predefined hemi-field sectors. Scores were assigned to probabilities for SRT at the level of 5%, 2.5% 1% and 0.5%. Per sector pair, a probability score limit (PSL) was calculated at each of the four levels and were compared with the scores obtained from the test cohort. The classification accuracy ‘normal versus abnormal’ was assessed for PSL in EMP and compared with glaucoma hemi-field test in standard automated perimetry. We found no statistically significant differences in SRTs between the mirror sectors in healthy subjects. The PSL at 2.5% had moderate classification accuracy with a specificity of 77% and sensitivity 70%. This could be suggestive of an SRT delay in the overall visual field in glaucoma.

A Strategy for Seeding Point Error Assessment for Retesting (SPEAR) in Perimetry Applied to Normal Subjects, Glaucoma Suspects, and Patients With Glaucoma

PURPOSE

We sought to determine the impact of seeding point errors (SPEs) as a source of low test reliability in perimetry and to develop a strategy to mitigate this error early in the test.

DESIGN

Cross-sectional study.

METHODS

Visual field test results from 1 eye of 364 patients (77 normal eyes, 178 glaucoma suspect eyes, and 109 glaucoma eyes) were used to develop models for identifying SPE. Two test cohorts (326 undertaking Swedish interactive thresholding algorithm [SITA]-Faster and 327 glaucoma eyes undertaking SITA-Standard) were used to prospectively evaluate the models for identifying SPEs. Global visual field metrics were compared among reliable and unreliable results. Regression models were used to identify factors distinguishing SPEs from non-SPEs. Models were evaluated using receiver operating characteristic (ROC) curves.

RESULTS

In the test cohorts, SITA-Faster produced a higher rate of unreliable visual field results (30%-49.7%) compared with SITA-Standard (10.8%-16.6%). SPEs contributed to most of the unreliable results in SITA-Faster (57.5%-64.9%) compared with gaze tracker deviations accounting for most of the unreliable results in SITA-Standard (40%-77.8%). In SITA-Faster, results with SPEs had worse global indices and more clusters of sensitivity reduction than reliable results. Our best model (using 9 test locations) can identify SPEs with an area under the ROC curve of 0.89.

CONCLUSION

SPEs contribute to a large proportion of unreliable visual field test results, particularly when using SITA-Faster. We propose a useful model for identifying SPEs early in the test that can then guide retesting using both SITA algorithms. We provide a simplified framework for the perimetrist to improve the overall fidelity of the test result.

Visual Field Plots: A Comparison Study Between Standard Automated Perimetry and Eye Movement Perimetry

PRéCIS:: This eye movement perimetry (EMP) study describes the development of saccadic reaction time (SRT)-based visual field plots, which could effectively display the presence, location, and extent of glaucomatous defects and support clinical decision-making.

PURPOSE

EMP is capable of discriminating normal from glaucomatous visual field defects on the basis of average delays in SRTs. To classify the presence and extent of age-corrected visual field defects, it is required to create SRT-based probability maps.

AIM

The aim of this study was to create visual field probability plots based on SRTs and to evaluate their clinical applicability by 2 glaucoma specialists.

MATERIALS AND METHODS

The development phase included 95 controls segregated into 5 age-bins to estimate normative limits of SRT. Next, for the testing phase, a set of 28 healthy subjects and 24 glaucoma patients were recruited who underwent standard automated perimetry (SAP) and EMP visual field testing. Fifty-two SAP and EMP plots were presented to 2 glaucoma specialists to classify them as normal or abnormal and to identify the defect location and pattern as 1 or more of 7 predefined categories.

RESULTS

The glaucoma specialists showed a sensitivity of 100% and a specificity of 93% and 96% for identifying normal versus abnormal visual field. For specialists 1 and 2, 85% and 92%, respectively, of EMP reports were assigned to the same category as SAP. The reports that did not agree with SAP were graded to a higher defect pattern. The intermethod agreement for specialists 1 and 2 was κ 0.92 and 0.96, respectively.

CONCLUSION

SRT-based visual field probability plots provided a comprehensive summary of an individual's visual field status and showed comparable clinical applicability to that of SAP plots.