Improving the robustness of the Sequentially Optimized Reconstruction Strategy (SORS) for visual field testing.

Perimetry, or visual field test, estimates differential light sensitivity thresholds across many locations in the visual field (e.g., 54 locations in the 24-2 grid). Recent developments have shown that an entire visual field may be relatively accurately reconstructed from measurements of a subset of these locations using a linear regression model. Here, we show that incorporating a dimensionality reduction layer can improve the robustness of this reconstruction. Specifically, we propose to use principal component analysis to transform the training dataset to a lower dimensional representation and then use this representation to reconstruct the visual field. We named our new reconstruction method the transformed-target principal component regression (TTPCR). When trained on a large dataset, our new method yielded results comparable with the original linear regression method, demonstrating that there is no underfitting associated with parameter reduction. However, when trained on a small dataset, our new method used on average 22% fewer trials to reach the same error. Our results suggest that dimensionality reduction techniques can improve the robustness of visual field testing reconstruction algorithms.

Using Fused Data from Perimetry and Optical Coherence Tomography to Improve the Detection of Visual Field Progression in Glaucoma.

Perimetry and optical coherence tomography (OCT) are both used to monitor glaucoma progression. However, combining these modalities can be a challenge due to differences in data types. To overcome this, we have developed an autoencoder data fusion (AEDF) model to learn compact encoding (AE-fused data) from both perimetry and OCT. The AEDF model, optimized specifically for visual field (VF) progression detection, incorporates an encoding loss to ensure the interpretation of the AE-fused data is similar to VF data while capturing key features from OCT measurements. For model training and evaluation, our study included 2504 longitudinal VF and OCT tests from 140 glaucoma patients. VF progression was determined from linear regression slopes of longitudinal mean deviations. Progression detection with AE-fused data was compared to VF-only data (standard clinical method) as well as data from a Bayesian linear regression (BLR) model. In the initial 2-year follow-up period, AE-fused data achieved a detection F1 score of 0.60 (95% CI: 0.57 to 0.62), significantly outperforming (p < 0.001) the clinical method (0.45, 95% CI: 0.43 to 0.47) and the BLR model (0.48, 95% CI: 0.45 to 0.51). The capacity of the AEDF model to generate clinically interpretable fused data that improves VF progression detection makes it a promising data integration tool in glaucoma management.

A Data-Driven Model for Simulating Longitudinal Visual Field Tests in Glaucoma.

Purpose: To develop a simulation model for glaucomatous longitudinal visual field (VF) tests with controlled progression rates. Methods: Longitudinal VF tests of 1008 eyes from 755 patients with glaucoma were used to learn the statistical characteristics of VF progression. The learned statistics and known anatomic correlations between VF test points were used to automatically generate progression patterns for baseline fields of patients with glaucoma. VF sequences were constructed by adding spatially correlated noise templates to the generated progression patterns. The two one-sided test (TOST) procedure was used to analyze the equivalence between simulated data and data from patients with glaucoma. VF progression detection rates in the simulated VF data were compared to those in patients with glaucoma using mean deviation (MD), cluster, and pointwise trend analysis. Results: VF indices (MD, pattern standard deviation), MD linear regression slopes, and progression detection rates for the simulated and patients' data were practically equivalent (TOST P < 0.01). In patients with glaucoma, the detection rates in 7 years using MD, cluster, and pointwise trend analysis were 24.4%, 26.2%, and 38.4%, respectively. In the simulated data, the mean detection rates (95% confidence interval) for MD, cluster, and pointwise trend analysis were 24.7% (24.1%-25.2%), 24.9% (24.2%-25.5%), and 35.7% (34.9%-36.5%), respectively. Conclusions: A novel simulation model generates glaucomatous VF sequences that are practically equivalent to longitudinal VFs from patients with glaucoma. Translational Relevance: Simulated VF sequences with controlled progression rates can support the evaluation and optimization of methods to detect VF progression and can provide guidance for the interpretation of longitudinal VFs.

Differences in attentional bias to smoking-related, affective, and sensation-seeking cues between smokers and non-smokers: an eye-tracking study.

RATIONALE: One of the behavioural features of tobacco use disorder is the presence of attentional bias (AB) to smoking-related stimuli. However, much of the research investigating these associations have been limited to the use of reaction-based indices. OBJECTIVES: We aimed to investigate differences in AB to smoking, affective, and sensation-seeking cues in smokers and non-smokers using novel, free-viewing, eye-tracking technology. Secondary aims included investigating impulsivity-by-group interaction effects on AB to sensation-seeking cues. METHODS: Participants were either otherwise-healthy smokers of at least 8 cigarettes per day or otherwise-healthy non-smokers (< 100 cigarettes in their lifetime and no smoking in the past year). AB was measured using a free-viewing, eye-tracking system. Participants were presented a series of slides divided into 3 themes: smoking, affective, and sensation-seeking. Each slide contained 4 images (1 theme-related, 1 neutral, 2 competitive). Primary outcome measure was the difference in the proportion of time spent viewing the theme-related cue to neutral cue. Impulsivity was measured using a monetary delayed discounting task. RESULTS: The sample consisted of 50 smokers (41 ± 12 years old) and 50 age- and sex-matched non-smokers (40 ± 14 years old). Smokers spent over 2 times longer looking at smoking-related images than non-smokers (F = 25.50, p < 0.001). As well, greater impulsivity was significantly associated with increased AB to sensation-seeking cues (R2 = 0.059, F = 2.98, p = 0.04) in smokers but not non-smokers. No differences were found on AB to affective cues. CONCLUSION: The eye-tracking procedure is a sensitive tool for assessing AB in smokers compared to non-smokers to both smoking and sensation-seeking cues.

Hybrid Eye-Tracking on a Smartphone with CNN Feature Extraction and an Infrared 3D Model.

This paper describes a low-cost, robust, and accurate remote eye-tracking system that uses an industrial prototype smartphone with integrated infrared illumination and camera. Numerous studies have demonstrated the beneficial use of eye-tracking in domains such as neurological and neuropsychiatric testing, advertising evaluation, pilot training, and automotive safety. Remote eye-tracking on a smartphone could enable the significant growth in the deployment of applications in these domains. Our system uses a 3D gaze-estimation model that enables accurate point-of-gaze (PoG) estimation with free head and device motion. To accurately determine the input eye features (pupil center and corneal reflections), the system uses Convolutional Neural Networks (CNNs) together with a novel center-of-mass output layer. The use of CNNs improves the system's robustness to the significant variability in the appearance of eye-images found in handheld eye trackers. The system was tested with 8 subjects with the device free to move in their hands and produced a gaze bias of 0.72°. Our hybrid approach that uses artificial illumination, a 3D gaze-estimation model, and a CNN feature extractor achieved an accuracy that is significantly (400%) better than current eye-tracking systems on smartphones that use natural illumination and machine-learning techniques to estimate the PoG.

Attention, novelty preference and the visual paired comparison task.

The innate ability of humans to identify, process and ascribe greater attentional resources (attention bias) to novel stimuli is essential for exploring new opportunities and consequently adapt to changing environments. One of the most common tests to assess attention bias to novel stimuli (Novelty Preference - NP) is the visual paired comparison task (VPC). In the VPC task subjects are presented with novel and previously seen images (repeated images) and NP is measured by parameters that describe visual scanning patterns on these images. The main objective of this study is to evaluate the effects of divided attention on NP. NP was measured in 26 healthy young individuals under two test conditions. In the first condition, subjects performed the VPC task and an audio task simultaneously (divided attention test condition), while in the second condition subjects performed only the VPC task (undivided attention test condition). For each test condition, repeated images were presented after delays ranging from 1.0 to 219.5 s and NP was measured by the mean difference between the relative fixation times on novel and repeated images at each delay. In the divided attention test condition, there were significant differences (p < 0.037) between the magnitudes of NPs for long delays (≥ 162 s) and short delays (≤12.5 s). Such differences were not detected in the undivided attention test condition. Analysis of variance revealed significant differences between the measured NPs during the divided and undivided attention test conditions (F(1, 25) = 18.38, p < 0.001, η2 = 0.424) and significant interaction effects between delays and testing conditions (F(5,125) = 2.88, p = 0.017, η2 = 0.103). Post-hoc t-tests showed significant differences between the measured NPs during the divided attention and undivided attention test conditions for long delays (162.0 and 219.5 s) but not for short delays (1.0 and 12.5 s). The results of the study are consistent with the hypothesis that for longer delays between the presentations of repeated images in the VPC task, NP is dependent on the recollection-based item recognition memory system, while for shorter delays NP is dependent on the automatic, familiarity-based item recognition memory system.

Effect of Methylphenidate for Apathy on Visual Attention Scanning Behavior: a Pilot Study.

BACKGROUND: The purpose of this pilot study was to explore the potential of eye-tracking technology in monitoring symptoms and predicting outcomes in apathetic Alzheimer's disease (AD) patients treated with methylphenidate (MTP). METHODS: Neuropsychological tests and eye-tracking measurements were completed at baseline and following at least four weeks of treatment with MTP (5-10 mg BID). Eye-movements were measured while patients viewed novel and social stimuli. Cognition, behavior, and apathy were assessed using the Standardized Mini-Mental State Exam (sMMSE), Neuropsychiatric Inventory, and Apathy Evaluation Scale (AES), respectively. RESULTS: Nine patients were included in the analysis (age: median=75, interquartile range=8; sMMSE: median=22, interquartile range=14). Spearman correlations showed that improvement on the AES was associated with increased visual attention towards novel stimuli (ρ7=-0.809, p=.008). Additionally, lower baseline attention towards social images was associated with improvement on the AES (ρ7=0.905, p=.001). CONCLUSIONS: Eye-tracking techniques can be developed as an objective and nonverbal method of monitoring symptoms and treatment outcomes in AD patients.

Accurate Model-Based Point of Gaze Estimation on Mobile Devices.

The most accurate remote Point of Gaze (PoG) estimation methods that allow free head movements use infrared light sources and cameras together with gaze estimation models. Current gaze estimation models were developed for desktop eye-tracking systems and assume that the relative roll between the system and the subjects' eyes (the 'R-Roll') is roughly constant during use. This assumption is not true for hand-held mobile-device-based eye-tracking systems. We present an analysis that shows the accuracy of estimating the PoG on screens of hand-held mobile devices depends on the magnitude of the R-Roll angle and the angular offset between the visual and optical axes of the individual viewer. We also describe a new method to determine the PoG which compensates for the effects of R-Roll on the accuracy of the POG. Experimental results on a prototype infrared smartphone show that for an R-Roll angle of 90 ° , the new method achieves accuracy of approximately 1 ° , while a gaze estimation method that assumes that the R-Roll angle remains constant achieves an accuracy of 3.5 ° . The manner in which the experimental PoG estimation errors increase with the increase in the R-Roll angle was consistent with the analysis. The method presented in this paper can improve significantly the performance of eye-tracking systems on hand-held mobile-devices.

Decreased Number of Self-Paced Saccades in Post-Concussion Syndrome Associated with Higher Symptom Burden and Reduced White Matter Integrity.

The aim of this study was to examine the potential utility of a self-paced saccadic eye movement as a marker of post-concussion syndrome (PCS) and monitoring the recovery from PCS. Fifty-nine persistently symptomatic participants with at least two concussions performed the self-paced saccade (SPS) task. We evaluated the relationships between the number of SPSs and 1) number of self-reported concussion symptoms, and 2) integrity of major white matter (WM) tracts (as measured by fractional anisotropy [FA] and mean diffusivity) that are directly or indirectly involved in saccadic eye movements and often affected by concussion. These tracts included the uncinate fasciculus (UF), cingulum (Cg) and its three subcomponents (subgenual, retrosplenial, and parahippocampal), superior longitudinal fasciculus, and corpus callosum. Mediation analyses were carried out to examine whether specific WM tracts (left UF and left subgenual Cg) mediated the relationship between the number of SPSs and 1) interval from last concussion or 2) total number of self-reported symptoms. The number of SPSs was negatively correlated with the total number of self-reported symptoms (r = -0.419, p = 0.026). The number of SPSs were positively correlated with FA of left UF and left Cg (r = 0.421, p = 0.013 and r = 0.452, p = 0.008; respectively). FA of the subgenual subcomponent of the left Cg partially mediated the relationship between the total number of symptoms and the number of SPSs, while FA of the left UF mediated the relationship between interval from last concussion and the number of SPSs. In conclusion, SPS testing as a fast and objective assessment may reflect symptom burden in patients with PCS. In addition, since the number of SPSs is associated with the integrity of some WM tracts, it may be useful as a diagnostic biomarker in patients with PCS.

Visual Selective Attention Toward Novel Stimuli Predicts Cognitive Decline in Alzheimer's Disease Patients.

BACKGROUND: Alzheimer's disease (AD) is associated with selective attention impairments, which could contribute to cognitive and functional deficits. Using visual scanning parameters, selective attention toward novel stimuli, or novelty preference, can be measured by a non-verbal, non-invasive method that may be of value in predicting disease progression. OBJECTIVE: In this longitudinal study, we explored whether novelty preference can predict cognitive decline in AD patients. METHODS: Mild to moderate AD patients viewed slides containing both novel and repeat images. The number of fixations, the average fixation time, and the relative fixation time on the two types of images were measured by an eye-tracking system. Novelty preference was estimated by the differences between the visual scanning parameters on novel and repeat images. Cognition and attention were assessed using the Standardized Mini-Mental Status Examination (sMMSE) and the Conners' Continuous Performance Test (CPT), respectively. Cognition was re-assessed every 6 months for up to 2 years. RESULTS: Multivariate linear regressions of 32 AD patients (14 females, age = 77.9±7.8, baseline sMMSE = 22.2±4.4) indicated that reduced time spent on novel images (t = 2.78, p = 0.010) was also associated with greater decline in sMMSE scores (R2 = 0.41, Adjusted R2 = 0.35, F3,28 = 6.51, p = 0.002), adjusting for attention and baseline sMMSE. CONCLUSION: These results suggest that novelty preference, measured by visual attention scanning technology, may reflect pathophysiological processes that could predict disease progression in the cognitively-impaired.

Apathy and Attentional Biases in Alzheimer's Disease.

BACKGROUND: Apathy, one of the most prevalent neuropsychiatric symptoms in Alzheimer's disease (AD), can be difficult to assess as cognition deteriorates. There is a need for more objective assessments that do not rely on patient insight, communicative capacities, or caregiver observation. OBJECTIVE: We measured visual scanning behavior, using an eye-tracker, to explore attentional bias in the presence of competing stimuli to assess apathy in AD patients. METHODS: Mild-to-moderate AD patients (Standardized Mini-Mental Status Examination, sMMSE >10) were assessed for apathy (Neuropsychiatric Inventory [NPI] apathy, Apathy Evaluation Scale [AES]). Participants were presented with 16 slides, each containing 4 images of different emotional themes (2 neutral, 1 social, 1 dysphoric). The duration of time spent, and fixation frequency on images were measured. RESULTS: Of the 36 AD patients (14 females, age = 78.2±7.8, sMMSE = 22.4±3.5) included, 17 had significant apathy (based on NPI apathy ≥4) and 19 did not. These groups had comparable age and sMMSE. Repeated-measures analysis of covariance models, controlling for total NPI, showed group (apathetic versus non-apathetic) by image (social versus dysphoric) interactions for duration (F(1,32) = 4.31, p = 0.046) and fixation frequency (F(1,32) = 11.34, p = 0.002). Apathetic patients demonstrated reduced duration and fixation frequency on social images compared with non-apathetic patients. Additionally, linear regression models suggest that more severe apathy predicted decreasing fixation frequency on social images (R2 = 0.26, Adjusted R2 = 0.19, F(3,32) = 3.65, p = 0.023). CONCLUSION: These results suggest that diminished attentional bias toward social-themed stimuli is a marker of apathy in AD. Measurements of visual scanning behavior may have the potential to predict and monitor treatment response in apathy.

Identifying Absolute Preferred Retinal Locations during Binocular Viewing.

PURPOSE: We present a new method for identifying the absolute location (i.e., relative to the optic disc) of the preferred retinal location (PRL) simultaneously for the two eyes of patients with central vision loss. For this, we used a binocular eye-tracking system that determines the pupillary axes of both eyes without a user calibration routine. METHODS: During monocular viewing, we measured the pupillary axis and the angle between it and the visual axis (angle Kappa) for 10 eyes with normal vision. We also determined their fovea location relative to the middle of the optic disc with the MP-1 microperimeter. Then, we created a transformation between the eye-tracking and microperimeter measurements. We used this transformation to predict the absolute location of the monocular and binocular PRLs of nine patients with central vision loss. The accuracy of the monocular prediction was evaluated with the microperimeter. The binocular PRLs were checked for retinal correspondence and functionality by placing them on fundus photographs. RESULTS: The transformation yielded an average error for the monocular measures of 0.2 (95% confidence interval, 1.0 to -0.6 degrees) horizontally and 0.5 (95% confidence interval, 1.1 to -0.1 degrees) vertically. The predicted binocular measures showed that the PRLs were generally in corresponding locations in the two eyes. One patient whose PRLs were not in corresponding positions complained about diplopia. For all patients, at least one PRL fell onto functional retina during binocular viewing. CONCLUSIONS: This study shows that measurements of the location of the binocular PRLs relative to the pupillary axes can be transformed into absolute locations.

Measuring Infant Visual Acuity with Gaze Tracker Monitored Visual Fixation.

PURPOSE: To validate a method of measuring grating acuity with remote gaze tracking (GT) against a current clinical test of visual acuity (VA), the Teller Acuity Cards (TACs), as part of the development of an automated VA test for infants. METHODS: Visual acuity for computer-generated horizontal square-wave gratings was determined from relative fixation time on a grating area compared with the background. In experiment 1, binocular VA was based on eye movements with a GT in 15 uncorrected myopic adults and compared with VA measured with subjective responses with the same stimuli and with the TACs. In experiment 2, binocular VA was determined in 19 typically developing infants aged 3 to 11 months on two visits with both the GT and TACs. RESULTS: In adults, the mean difference between VA measured by the GT and TACs was 0.01 log cycles per degree (cpd) and the 95% limits of agreement were 0.11. One hundred percent of GT VA results were within 0.5 octave of the TACs' VAs. The mean difference between the GT and TACs for infants was 0.17 log cpd on both the first and second visit (95% limits of agreement, 0.42 and 0.47, respectively). The mean difference between test and retest for infant GT VA was 0.06 log cpd, and limits of agreement for repeatability were 0.48 log cpd. In infants, both the TACs and the GT had a reliability of 89% within less than or equal to 1 octave between visits. Gaze tracking VA improved with age and is in agreement with published norms. CONCLUSIONS: The agreement between the TACs and GT in adults and infants validates the method of measuring grating acuity with the remote GT. These results demonstrate its potential for an automated test of infant VA.

Exploring Visual Selective Attention towards Novel Stimuli in Alzheimer's Disease Patients.

BACKGROUND: Alzheimer's disease (AD) is associated with selective attention impairments, which could contribute to cognitive and functional deficits. Selective attention can be explored through examination of novelty preference. AIMS: In this study, we quantified novelty preference in AD patients by measuring visual scanning behaviour using an eye tracking paradigm. METHODS: Mild-to-moderate AD patients and elderly controls viewed slides containing novel and repeated images simultaneously. The outcome measure was time spent on specific images, with novelty preference defined by greater relative fixation time (RFT) on novel versus repeated images. Cognitive status (Standardized Mini-Mental State Examination, SMMSE) and attention (Digit Span, DS) were also measured. RESULTS: AD patients (age 79.2 ± 6.7 years, SMMSE 22.2 ± 4.0, n = 41) and controls (age 76.2 ± 6.4 years, SMMSE 28.1 ± 2.0, n = 24) were similar in age, education and sex. Compared with controls, AD patients had lower RFT on novel than on repeated images (F1,63 = 11.18, p = 0.001). Further, reduced RFT was associated with lower scores on SMMSE (r63 = 0.288, p = 0.020) and DS (r63 = 0.269, p = 0.030). Within individuals, novelty preference was detected in 92.3% of patients and in 100% of controls. CONCLUSION: These findings suggest that novelty preference, measured by visual scanning behaviour, can differentiate cognitively healthy and impaired people and may offer a nonverbal, less cognitively demanding method of assessing selective attention.

Attentional biases to body shape images in adolescents with anorexia nervosa: an exploratory eye-tracking study.

Body image distortion (BID) plays an important role in the etiology and maintenance of anorexia nervosa (AN). Previous studies of BID in AN showed small biases in visual scanning behavior (VSB) towards images of body shapes. The aim of this study is to investigate biases in VSB when body shape images compete with images with a different theme (social interactions) for subjects׳ attention. When images of thin body shapes (TBS) were presented alongside images of social interactions, AN patients (n=13) spent significantly more time looking at TBSs rather than at social interactions, but controls (n=20) did not. When images of fat body shapes (FBS) were presented alongside images of social interactions, AN patients spent significantly more time looking at FBSs rather than at social interactions, but controls did not. When images of TBSs, FBSs and social interactions were presented alongside each other, AN patients demonstrated a hierarchy in their attention allocation, choosing to spend the most viewing time on TBS images, followed by FBS images and then images with social interactions. Under the three experimental conditions, AN patients demonstrated large biases in their visual scanning behavior (VSB). Biases in VSB may provide physiologically objective measures that characterize patients with AN.

Gaze patterns and audiovisual speech enhancement.

PURPOSE: In this study, the authors sought to quantify the relationships between speech intelligibility (perception) and gaze patterns under different auditory-visual conditions. METHOD: Eleven subjects listened to low-context sentences spoken by a single talker while viewing the face of one or more talkers on a computer display. Subjects either maintained their gaze at a specific distance (0°, 2.5°, 5°, 10°, and 15°) from the center of the talker's mouth (CTM) or moved their eyes freely on the computer display. Eye movements were monitored with an eye-tracking system, and speech intelligibility was evaluated by the mean percentage of correctly perceived words. RESULTS: With a single talker and a fixed point of gaze, speech intelligibility was similar for all fixations within 10° of the CTM. With visual cues from two talker faces and a speech signal from one of the talkers, speech intelligibility was similar to that of a single talker for fixations within 2.5° of the CTM. With natural viewing of a single talker, gaze strategy changed with speech-signal-to-noise ratio (SNR). For low speech-SNR, a strategy that brought the point of gaze directly to within 2.5° of the CTM was used in approximately 80% of trials, whereas in high speech-SNR it was used in only approximately 50% of trials. CONCLUSIONS: With natural viewing of a single talker and high speech-SNR, subjects can shift their gaze between points on the talker's face without compromising speech intelligibility. With low-speech SNR, subjects change their gaze patterns to fixate primarily on points that are in close proximity to the talker's mouth. The latter strategy is essential to optimize speech intelligibility in situations where there are simultaneous visual cues from multiple talkers (i.e., when some of the visual cues are distracters).

Antisaccade generation is impaired after parietal lobe lesions.

Antisaccades are directed away from visual targets. Impaired antisaccade generation has been attributed to frontal lobe damage. We studied antisaccades in patients with unilateral focal parietal lobe lesions. Normal subjects (N = 10) instructed to make 10° antisaccades opposite to a 100-ms target flash 10° to the right or left of center made antisaccades in 86.1% of trials. Patients (N = 13) made antisaccades contraversive to their lesions in 55.4% of trials and 50.5% of ipsiversive trials. In other trials, reflexive saccades occurred toward the target flash. Nine patients with imaged lesions overlapping in parietal lobe white matter showed subnormal antisaccade generation. Antisaccades provide a means of measuring voluntary saccade function of the parietal lobes independent of visual guidance. Impaired suppression of reflexive saccades and generation of antisaccades is attributed to disconnection of parietal lobe from frontal lobe ocular motor areas.

An automated Hirschberg test for infants.

A novel automated method to measure eye misalignment in infants is presented. The method uses estimates of the Hirschberg ratio (HR) and angle Kappa (the angle between the visual and optical axis) for each infant to calculate the angle of eye misalignment. The HR and angle Kappa are estimated automatically from measurements of the direction of the optical axis and the coordinates of the center of the entrance pupil and corneal reflexes in each eye when infants look at a set of images that are presented sequentially on a computer monitor. The HR is determined by the slope of the line that describes the direction of the optical axis as a function of the distance between the center of the entrance pupil and the corneal reflexes. The peak of the distribution of possible angles Kappa during the image presentation determines the value of angle Kappa. Experiments with five infants showed that the 95% limits of agreement between repeated measurements of angle Kappa are ± 0.61 (°). The maximum error in the estimation of eye alignment in orthotropic infants was 0.9 (°) with 95% limits of agreement between repeated measurements of 0.75 (°).

Objective estimation of visual acuity with preferential looking.

PURPOSE: A novel preferential looking (PL) procedure that uses quantitative analysis of visual scanning parameters is presented. METHODS: Nine adult subjects were presented with a set of 14 visual stimuli (stimuli included three uniform gray fields and one field with black-and-white square wave gratings) spanning the range of spatial frequencies from 1.5 cyc/deg to 35.1 cyc/deg (1.3 logMAR to -0.07 logMAR). A remote gaze-tracking system was used to monitor the subject's eye movements and the relative fixation time (RFT) on the grating target. Subsequently, a four alternative forced-choice psychophysical test (4AFC) was performed with the same visual stimuli. RESULTS: For visual stimuli for which the gratings' positions in the 4AFC test were identified correctly in 100% of the trials (reliably discriminated), the mean RFT was 72.5% ± 9.0%. For stimuli for which the spatial frequencies were higher than the subject's psychophysically determined visual acuity (VA) threshold (nondiscriminated), the mean RFT was 25.3% ± 8.5%. Using three repeated trials at each spatial frequency and a VA detector based on the conditional probability density functions of the RFT, the average VA was underestimated by 0.06 logMAR (range, 0.00-0.20 logMAR). CONCLUSIONS: In adults, automated quantitative analysis of visual scanning patterns can be used to estimate VA objectively and rapidly (210 seconds) with a mean error of 0.06 logMAR. The novel approach may form the basis for PL procedures that are more objective and more accurate than the traditional clinical PL procedures.

Fixation-free assessment of the Hirschberg ratio.

PURPOSE: To describe a novel methodology by which to measure the Hirschberg ratio (HR) in infants. The methodology does not require fixation on specific points, and measurements are made while infants look naturally at a display. METHODS: The HR is calculated automatically from measurements of the direction of the optical axis, the position of the pupil center, and corneal reflexes in video images from an advanced two-camera eye-tracking system. The performance of the novel fixation-free procedure (FFP) was evaluated in 43 adults by measuring the average difference and the 95% limits of agreement with the standard fixation-based procedure (FBP). Repeatability of the HR measurements was evaluated by assessing the 95% limits of agreement between two independent measurements. Performance of the FFP was also evaluated in five infants. RESULTS: In adults, the average HR was 12.89 +/- 1.22 degrees/mm for FFP and 12.81 +/- 1.22 degrees/mm for FBP. FFP and FBP measurements were highly correlated (r = 0.95; P < 0.001). The 95% limits of agreement between FFP and FBP were +/-0.86 degrees/mm. The 95% limits of agreement of repeated measurements were +/-0.66 degrees/mm for FFP and +/-0.77 degrees/mm for FBP. In infants, the 95% limits of agreement of repeated measurements by FFP were +/-0.63 degrees/mm. CONCLUSIONS: In adults, the FFP provides accurate measurements of the HR that are in excellent agreement with measurements by FBP. In infants, measurements of HR by FFP show the same repeatability and consistency.