Harry M. Brash

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.

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.

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.

Increased sensitivity of rabbit carotid body chemoreceptors to dopamine after chronic treatment with domperidone

An increase in specific dopamine D2 receptor binding sites was observed in membranes prepared from the carotid bodies of rabbits treated for 8 weeks and then withdrawn for 4-9 days from the D2 antagonist domperidone (2-5 mg/kg per day). Recordings of chemoreceptor afferent discharge from the carotid body also revealed that this change in receptor density was accompanied by an increased sensitivity to the chemodepressant effects of exogenous dopamine. The chemoreceptor responsiveness of the carotid body to hypoxia is blunted in rabbits treated chronically with domperidone, but this can be restored to normal by an acute dose of the D2 antagonist. These experiments provide evidence that is compatible with a chemo-inhibitory role for endogenous dopamine in the rabbits carotid body. Furthermore, these results suggest that the carotid body provides a useful model for the functional studies of dopamine D2 receptors.

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.

Detection and characterisation of visual field defects using Saccadic Vector Optokinetic Perimetry in children with brain tumours

PurposeTo determine the ability of Saccadic Vector Optokinetic Perimetry (SVOP) to detect and characterise visual field defects in children with brain tumours using eye-tracking technology, as current techniques for assessment of visual fields in young children can be subjective and lack useful detail.MethodsCase-series study of children receiving treatment and follow-up for brain tumours at the Royal Hospital for Sick Children in Edinburgh from April 2008 to August 2013. Patients underwent SVOP testing and the results were compared with clinically expected visual field patterns determined by a consensus panel after review of clinical findings, neuroimaging, and where possible other forms of visual field assessment.ResultsSixteen patients participated in this study (mean age of 7.2 years; range 2.9–15 years; 7 male, 9 female). Twelve children (75%) successfully performed SVOP testing. SVOP had a sensitivity of 100% and a specificity of 50% (positive predictive value of 80% and negative predictive value of 100%). In the true positive and true negative SVOP results, the characteristics of the SVOP plots showed agreement with the expected visual field. Six patients were able to perform both SVOP and Goldmann perimetry, these demonstrated similar visual fields in every case.ConclusionSVOP is a highly sensitive test that may prove to be extremely useful for assessing the visual field in young children with brain tumours, as it is able to characterise the central 30° of visual field in greater detail than previously possible with older techniques.

Comparison of Threshold Saccadic Vector Optokinetic Perimetry (SVOP) and Standard Automated Perimetry (SAP) in Glaucoma. Part II: Patterns of Visual Field Loss and Acceptability

Purpose We compared patterns of visual field loss detected by standard automated perimetry (SAP) to saccadic vector optokinetic perimetry (SVOP) and examined patient perceptions of each test. Methods A cross-sectional study was done of 58 healthy subjects and 103 with glaucoma who were tested using SAP and two versions of SVOP (v1 and v2). Visual fields from both devices were categorized by masked graders as: 0, normal; 1, paracentral defect; 2, nasal step; 3, arcuate defect; 4, altitudinal; 5, biarcuate; and 6, end-stage field loss. SVOP and SAP classifications were cross-tabulated. Subjects completed a questionnaire on their opinions of each test. Results We analyzed 142 (v1) and 111 (v2) SVOP and SAP test pairs. SVOP v2 had a sensitivity of 97.7% and specificity of 77.9% for identifying normal versus abnormal visual fields. SAP and SVOP v2 classifications showed complete agreement in 54% of glaucoma patients, with a further 23% disagreeing by one category. On repeat testing, 86% of SVOP v2 classifications agreed with the previous test, compared to 91% of SAP classifications; 71% of subjects preferred SVOP compared to 20% who preferred SAP. Conclusions Eye-tracking perimetry can be used to obtain threshold visual field sensitivity values in patients with glaucoma and produce maps of visual field defects, with patterns exhibiting close agreement to SAP. Patients preferred eye-tracking perimetry compared to SAP. Translational relevance This first report of threshold eye tracking perimetry shows good agreement with conventional automated perimetry and provides a benchmark for future iterations.