Ian C. Murray

Feasibility of Saccadic Vector Optokinetic Perimetry: A Method of Automated Static Perimetry for Children Using Eye Tracking

PURPOSE To determine the feasibility of a new technique for suprathreshold automated static perimetry in children. DESIGN Evaluation of diagnostic test or technology. PARTICIPANTS The study included 29 subjects comprising 4 groups: 12 adults with normal fields, 4 children aged less than 10 years with normal fields, 8 adults with visual field defect, and 5 children aged less than 10 years with suspected visual field defects. METHODS The system comprises a personal computer, display, and eye tracker to monitor gaze position when stimuli are presented in the visual field. The natural saccadic eye movement to fixate on the stimuli, if seen, can be detected and measured to produce a visual field plot. Subjects performed 3 eye-tracking tests, unless unable to do so for any reason: a 40-point binocular test and two 41-point tests for each eye. The tests were based on the Humphrey Field Analyzer (HFA) Central-40 point screening test with a stimulus size of Goldmann III and intensity of 14 decibels (dB). Adults also performed the equivalent Humphrey screening test in each eye for comparison. MAIN OUTCOME MEASURES Comparison of visual field plot results between the eye-tracking tests and HFA tests in adults. Correlation between the eye-tracking tests and the clinical assessment in the children with suspected visual field defects. RESULTS In the eyes of all normal adult and child subjects performing the eye-tracking test, the percentage of points in agreement with a healthy visual field was 99.2% and 99.1%, respectively. The percentage of points agreeing with the HFAs screening test in the adult eyes with visual field defects was 89.8%. Visual field defects were also correctly identified by the eye-tracking system in the eyes of children with suspected visual field defects. CONCLUSIONS The results demonstrate that suprathreshold automated static perimetry using eye tracking is a promising method of perimetry for use with children.

Automatic blood pressure measurement: the oscillometric waveform shape is a potential contributor to differences between oscillometric and auscultatory pressure measurements

Objective To explore the differences between oscillometric and auscultatory measurements. Method From a simulator evaluation of a non-invasive blood pressure (NIBP) device regenerating 242 oscillometric blood pressure waveforms from 124 subjects, 10 waveforms were selected based on the differences between the NIBP (oscillometric) and auscultatory pressure measurements. Two waveforms were selected for each of five criteria: systolic over and underestimation; diastolic over and underestimation; and close agreement for both systolic and diastolic pressures. The 10 waveforms were presented to seven different devices and the oscillometric–auscultatory pressure differences were compared between devices and with the oscillometric waveform shapes. Results Consistent patterns of waveform-dependent over and underestimation of systolic and diastolic pressures were shown for all seven devices. The mean and standard deviation, for all devices, of oscillometric–auscultatory pressure differences were: for the systolic overestimated waveforms, 36 ± 28/−6 ± 3 and 23 ± 2/−1 ± 3 mmHg (systolic/diastolic differences); for systolic underestimated waveforms, −21 ± 5/−4 ± 3 and −11 ± 4/−3 ± 3 mmHg; for diastolic overestimated waveforms, 3 ± 4/12 ± 5 and 17 ± 6/10 ± 2 mmHg; for diastolic underestimated waveforms, 1 ± 4/−22 ± 4 and −9 ± 6/−29 ± 4 mmHg; and for the two waveforms with good agreement, 0 ± 6/0 ± 3 and −2 ± 4/−4 ± 3 mmHg. Waveforms for which devices showed good oscillometric and auscultatory agreement had smooth envelopes with clearly defined peaks, compared with the broader plateau and complex shapes of those waveforms for which devices over or underestimated pressures. Conclusion By increasing the understanding of the characteristics and limitations of the oscillometric method and the effects of waveform shape on pressure measurements, simulator evaluation should lead to improvements in NIBP devices.

Effect of the shapes of the oscillometric pulse amplitude envelopes and their characteristic ratios on the differences between auscultatory and oscillometric blood pressure measurements.

IntroductionOscillometric noninvasive blood pressure (NIBP) devices determine pressure by analysing the oscillometric waveform using empirical algorithms. Many algorithms analyse the waveform by calculating the systolic and diastolic characteristic ratios, which are the amplitudes of the oscillometric pulses in the cuff at, respectively, the systolic and diastolic pressures, divided by the peak pulse amplitude. A database of oscillometric waveforms was used to study the influences of the characteristic ratios on the differences between auscultatory and oscillometric measurements. MethodsTwo hundred and forty-three oscillometric waveforms and simultaneous auscultatory blood pressures were recorded from 124 patients at cuff deflation rates of 2–3 mmHg/s. A simulator regenerated the waveforms, which were presented to two NIBP devices, the Omron HEM-907 [OMRON Europe B.V. (OMCE), Hoofddorp, The Netherlands] and the GE ProCare 400 (GE Healthcare, Tampa, Florida, USA). For each waveform, the paired systolic and paired diastolic pressure differences between device measurements and auscultatory reference pressures were calculated. The systolic and diastolic characteristic ratios, corresponding to the reference auscultatory pressures of each oscillometric waveform stored in the simulator, were calculated. The paired differences between NIBP measured and auscultatory reference pressures were compared with the characteristic ratios. ResultsThe mean and standard deviations of the systolic and diastolic characteristic ratios were 0.49 (0.11) and 0.72 (0.12), respectively. The systolic pressures recorded by both devices were lower (negative paired pressure difference) than the corresponding auscultatory pressures at low systolic characteristic ratios, but higher than the corresponding auscultatory pressures at high systolic pressures. Conversely, the differences between the paired diastolic pressure differences were higher at low diastolic characteristic ratios, compared with those at high diastolic characteristic ratios. The paired systolic pressure differences were within ±5 mmHg for those waveforms with systolic characteristic ratios between 0.4 and 0.7 for the Omron and between 0.3 and 0.5 for the ProCare. The paired diastolic pressure differences were within ±5 mmHg for those waveforms with diastolic characteristic ratios between 0.4 and 0.6 for the Omron and between 0.5 and 0.8 for the ProCare. Discussion and conclusionThe systolic and diastolic paired oscillometric–auscultatory pressure differences varied with their corresponding characteristic ratios. Good agreement (within 5 mmHg) between the oscillometric and auscultatory pressures occurred for oscillometric pulse amplitude envelopes with specific ranges of characteristic ratios, but the ranges were different for the two devices. Further work is required to classify the different envelope shapes, comparing them with patient conditions, to determine if a clearer understanding of the different waveform shapes would improve the accuracy of oscillometric measurements.

Validation of oscillometric noninvasive blood pressure measurement devices using simulators

Oscillometric noninvasive blood pressure devices measure blood pressure using an indirect method and proprietary algorithms and hence require validation in clinical trials. Clinical trials are, however, expensive and give contradictory results, and validated devices are not accurate in all patient groups. Simulators that regenerate oscillometric waveforms promise an alternative to clinical trials provided they include sufficient physiological and pathological oscillometric waveforms. Simulators should also improve the understanding of the oscillometric method.

Saccadic Vector Optokinetic Perimetry (SVOP): A novel technique for automated static perimetry in children using eye tracking

Perimetry is essential for identifying visual field defects due to disorders of the eye and brain. However, young children are often unable to reliably perform the preferred method of visual field assessment known as automated static perimetry (ASP). This paper introduces a novel method of ASP specifically developed for children called Saccadic Vector Optokinetic Perimetry (SVOP). SVOP uses eye tracking to detect the natural saccadic eye response of gaze orientation towards visual field stimuli if they are seen. In this paper, the direction and magnitude of a sample of subject gaze responses to visual field stimuli is used to construct a software decision algorithm for use in SVOP. SVOP was clinically evaluated in a group of 24 subjects, comprising children and adults, with and without visual field defects, by comparison with an equivalent test on the Humphrey Field Analyser (HFA). SVOP provides promising visual field test results when compared with the reference HFA test, and has proven extremely useful in detecting visual field defects in children unable to perform traditional ASP.

Multiple Measures of Fixation on Social Content in Infancy: Evidence for a Single Social Cognitive Construct?

The preference of infants to fixate on social information in a stimulus is well known. We examine how this preference manifests across a series of free‐viewing tasks using different stimulus types. Participants were thirty typically developing infants. We measured eye movements when viewing isolated faces, faces alongside objects in a grid, and faces naturally presented in photographed scenes. In each task, infants fixated social content for longer than nonsocial content. Social preference scores representing distribution of fixation to social versus general image content were highly correlated and thus combined into a single composite measure, which was independent of demographic and behavioral measures. We infer that multiple eye‐tracking tasks can be used to generate a composite measure of social preference in infancy. This approach may prove useful in the early characterization of developmental disabilities.

Oscillometric Noninvasive Blood Pressure Measurement Devices and Simulators

Unless users of oscillometric noninvasive blood pressure simulators understand both the indirect nature of the oscillometric method and its empirical implementation, they can misunderstand the performances of both noninvasive blood pressure devices and simulators. The article describes the variation in the oscillometric pulses with cuff pressure, leading to an overview of the characteristics, limitations, and applications of simulators. The differences between pressures recorded by noninvasive blood pressure devices and simulator settings are explained, emphasizing that unless the simulator uses physiologic oscillometric envelopes, the differences do not necessarily imply lack of calibration of noninvasive blood pressure device or simulator. Simulator functional specifications are described, advocating that simulators include physiologic oscillometric envelopes and pulse waveforms.

Feasibility, Accuracy, and Repeatability of Suprathreshold Saccadic Vector Optokinetic Perimetry.

Purpose To evaluate feasibility, accuracy, and repeatability of suprathreshold Saccadic Vector Optokinetic Perimetry (SVOP) by comparison with Humphrey Field Analyzer (HFA) perimetry. Methods The subjects included children with suspected field defects (n = 10, age 5–15 years), adults with field defects (n = 33, age 39–78 years), healthy children (n = 12, age 6–14 years), and healthy adults (n = 30, age 16–61 years). The test protocol comprised repeat suprathreshold SVOP and HFA testing with the C-40 test pattern. Feasibility was assessed by protocol completeness. Sensitivity, specificity, and accuracy of SVOP was established by comparison with reliable HFA tests in two ways: (1) visual field pattern results (normal/abnormal), and (2) individual test point outcomes (seen/unseen). Repeatability of each test type was assessed using Cohens kappa coefficient. Results Of subjects, 82% completed a full protocol. Poor reliability of HFA testing in child patients limited the robustness of comparisons in this group. Sensitivity, specificity, and accuracy across all groups when analyzing the visual field pattern results was 90.9%, 88.5%, and 89.0%, respectively, and was 69.1%, 96.9%, and 95.0%, respectively, when analyzing the individual test points. Cohens kappa coefficient for repeatability of SVOP and HFA was excellent (0.87 and 0.88, respectively) when assessing visual field pattern results, and substantial (0.62 and 0.74, respectively) when assessing test point outcomes. Conclusions SVOP was accurate in this group of adults. Further studies are required to assess SVOP in child patient groups. Translational Relevance SVOP technology is still in its infancy but is used in a number of centers. It will undergo iterative improvements and this study provides a benchmark for future iterations.

Correcting LCD luminance non-uniformity for threshold Saccadic Vector Optokinetic Perimetry (SVOP)

The accurate assessment of visual field function can provide valuable information on a range of visual disorders. Saccadic Vector Optokinetic Perimetry (SVOP) is a novel instrument for measuring supra-threshold visual fields in young children who are otherwise unable to perform Automated Static Perimetry (ASP). However, limitations in Liquid Crystal Display (LCD) technology restrict the ability of SVOP to determine threshold values at various points in the visual field, often required in detailed perimetry examinations. This paper introduces a purpose-specific LCD luminance non-uniformity compensation approach to address this limitation. Thorough quantitative evaluation identifies the effectiveness of the proposed approach in (i) compensating for luminance non-uniformities across an LCD, and (ii) enabling SVOP to perform accurate and precise threshold visual field tests. The findings demonstrate that SVOP provides a promising alternative to the current threshold ASP standard (Humphrey Field Analyser).

Comparison of saccadic vector optokinetic perimetry and standard automated perimetry in glaucoma. Part I: Threshold values and repeatability

Purpose We evaluated threshold saccadic vector optokinetic perimetry (SVOP) and compared results to standard automated perimetry (SAP). Methods A cross-sectional study was done including 162 subjects (103 with glaucoma and 59 healthy subjects) recruited at a university hospital. All subjects underwent SAP and threshold SVOP. SVOP uses an eye tracker to monitor eye movement responses to stimuli and determines if stimuli have been perceived based on the vector of the gaze response. The test pattern used was equivalent to SAP 24-2 and stimuli were presented at Goldmann III. Average and pointwise sensitivity values obtained from both tests were compared using Pearsons correlation coefficient. Two versions of SVOP were evaluated. Results A total of 124 tests were performed with SAP and SVOP version 2. There was excellent agreement between mean threshold values obtained using SVOP and SAP (r = 0.95, P < 0.001). Excluding the blind spot, correlation between SVOP and SAP individual test point sensitivity ranged from 0.61 to 0.90, with 48 of 54 (89%) test points > 0.70. Overall SVOP showed good repeatability with a Pearson correlation of 0.88. The repeatability on a point-by-point basis ranged from 0.66 to 0.98, with 45 of 54 points (83%) > 0.80. Repeatability of SAP was 0.87, ranging from 0.69 to 0.96, with 47 of 54 (87%) points > 0.80. Conclusion Eye-tracking perimetry is repeatable and compares well with the current gold standard of SAP. The technique has advantages over conventional perimetry and could be useful for evaluating glaucomatous visual field loss, particularly in patients who may struggle with conventional perimetry. Translational Relevance Suprathreshold SVOP already is in the field. To our knowledge, this is the first report of threshold SVOP and provides a benchmark for future iterations.