Optometry and Vision Sciences - Research Publications

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    Exercise alone impacts short-term adult visual neuroplasticity in a monocular deprivation paradigm
    Virathone, L ; Nguyen, BN ; Dobson, F ; Carter, OL ; McKendrick, AM (ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2021-10-01)
    Adult homeostatic visual plasticity can be induced by short-term patching, heralded by a shift in ocular dominance in favor of the deprived eye after monocular occlusion. The potential to boost visual neuroplasticity with environmental enrichment such as exercise has also been explored; however, the results are inconsistent, with some studies finding no additive effect of exercise. Studies to date have only considered the effect of patching alone or in combination with exercise. Whether exercise alone affects typical outcome measures of experimental estimates of short-term visual neuroplasticity is unknown. We therefore measured binocular rivalry in 20 healthy young adults (20-34 years old) at baseline and after three 2-hour interventions: patching (of the dominant eye) only, patching with exercise, and exercise only. Consistent with previous work, the patching interventions produced a shift in ocular dominance toward the deprived (dominant) eye. Mild- to moderate-intensity exercise in the absence of patching had several effects on binocular rivalry metrics, including a reduction in the dominant eye percept. The proportion of mixed percept and the time to first switch (onset rivalry) did not change from baseline across all interventions. Thus, we demonstrate that exercise alone can impact binocular rivalry outcomes measures. We did not observe a synergistic effect between patching and exercise in our data.
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    Developing a Screening Tool for Areas of Abnormal Central Vision Using Visual Stimuli With Natural Scene Statistics
    Srinivasan, R ; Turpin, A ; McKendrick, AM (ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2022-02-01)
    PURPOSE: Previous studies show that some visual field (VF) defects are detectable from visual search behavior; for example, when watching video. Here, we developed and tested a VF testing approach that measures the number of fixations to find targets on a background with spatial frequency content similar to natural scenes. METHODS: Twenty-one older controls and 20 people with glaucoma participated. Participants searched for a Gabor (6 c/°) that appeared in one of 25 possible locations within a 15° (visual angle) 1/f noise background (RMS contrast: 0.20). Procedure performance was assessed by calculating sensitivity and specificity for different combinations of control performance limits (p = 95%, 98%, 99%), number of target locations with fixations outside control performance limits (k = 0 to 25) and number of repeated target presentations (n = 1 to 20). RESULTS: Controls made a median of two to three fixations (twenty-fifth to seventy-fifth percentile: two to four) to locate the target depending on location. A VF was flagged "abnormal" when the number of fixations was greater than the p = 99% for k = 3 or more locations with n = 2 repeated presentations, giving 85% sensitivity and 95.2% specificity. The median test time for controls was 85.71 (twenty-fifth to seventy-fifth percentile: 66.49-113.53) seconds. CONCLUSION: Our prototype test demonstrated effective and efficient screening of abnormal areas in central vision. TRANSLATIONAL RELEVANCE: Visual search behavior can be used to detect central vision loss and may produce results that relate well to performance in natural visual environments.
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    Do Additional Testing Locations Improve the Detection of Macular Perimetric Defects in Glaucoma?
    Montesano, G ; McKendrick, AM ; Turpin, A ; Brusini, P ; Oddone, F ; Fogagnolo, P ; Perdicchi, A ; Johnson, CA ; Lanzetta, P ; Rossetti, LM ; Garway-Heath, DF ; Crabb, DP (ELSEVIER SCIENCE INC, 2021-11-18)
    PURPOSE: To evaluate the ability of additional central testing locations to improve detection of macular visual field (VF) defects in glaucoma. DESIGN: Prospective cross-sectional study. PARTICIPANTS: Four hundred forty healthy people and 499 patients with glaucomatous optic neuropathy (GON) were tested with a fundus tracked perimeter (CMP; CenterVue) using a 24-2 grid with 12 additional macular locations (24-2+). METHODS: Glaucomatous optic neuropathy was identified based on expert evaluation of optic nerve head photographs and OCT scans, independently of the VF. We defined macular defects as locations with measurements outside the 5% and 2% normative limits on total deviation (TD) and pattern deviation (PD) maps within the VF central 10°. Classification was based on the total number of affected macular locations (overall detection) or the largest number of affected macular locations connected in a contiguous cluster (cluster detection). Criteria based on the number of locations and cluster size were used to obtain equivalent specificity between the 24-2 grid and the 24-2+ grids, calculated using false detections in the healthy cohort. Partial areas under the receiver operating characteristic curve (pAUCs) were also compared at specificities of 95% or more. MAIN OUTCOME MEASURES: Matched specificity comparison of the ability to detect glaucomatous macular defects between the 24-2 and 24-2+ grids. RESULTS: At matched specificity, cluster detection identified more macular defects with the 24-2+ grid compared with the 24-2 grid. For example, the mean increase in percentage of detection was 8% (95% confidence interval [CI], 5%-11%) and 10% (95% CI, 7%-13%) for 5% TD and PD maps, respectively, and 5% (95% CI, 2%-7%) and 6% (95% CI, 4%-8%) for the 2% TD and PD maps, respectively. Good agreement was found between the 2 grids. The improvement measured by pAUCs was also significant but generally small. The percentage of eyes with macular defects ranged from about 30% to 50%. Test time for the 24-2+ grid was longer (21% increase) for both cohorts. Between 74% and 98% of defects missed by the 24-2 grid had at least 1 location with sensitivity of < 20 dB. CONCLUSIONS: Visual field examinations with additional macular locations can improve the detection of macular defects in GON modestly without loss of specificity when appropriate criteria are selected.
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    A Method for Reducing the Number of Presentations in Perimetric Test Procedures.
    Turpin, A ; McKendrick, AM (Association for Research in Vision and Ophthalmology (ARVO), 2022-04-01)
    Purpose: To introduce a new method (ARBON) for decreasing the test time of psychophysical procedures and examine its application to perimetry. Methods: ARBON runs in parallel with an existing psychophysical procedure injecting occasional responses of seen or unseen into that procedure. Using computer simulation to mimic human responses during perimetry, we assess the performance of ARBON relative to an underlying test procedure and a version of that procedure truncated to be faster. Simulations used 610 normal eyes (age 20 to 80 years) and 163 glaucoma eyes (median mean deviation = -1.81 dB, 5th percentile = +2.14 dB, 95th percentile = -22.55 dB). Outcome measures were number of presentations and mean absolute error in threshold estimation. We also examined the probability distribution of measured thresholds. Results: ARBON and the Truncated procedure reduced presentations by 16% and 18%, respectively. Mean error was increased by 8% to 10% for the Truncated procedure but decreased by 5% to 7% for ARBON. The probability distributions of measured thresholds using ARBON overlapped with the Underlying procedure by over 80%, whereas the Truncated procedure overlapped by 50%. Conclusions: ARBON offers a principled method for reducing test time. ARBON can be added to any existing psychophysical procedure without requiring any change to the logic or parameters controlling the procedure, resulting in distributions of measured thresholds similar to those of the underlying procedure. Translational Relevance: ARBON can be added to a perimetry test procedure to speed up the test while largely preserving the distribution of returned sensitivities, thus producing normative data similar to the data for the original, underlying perimetric test.
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    The Open Perimetry Initiative: A framework for cross-platform development for the new generation of portable perimeters
    Marin-Franch, I ; Turpin, A ; Artes, PH ; Chong, LX ; McKendrick, AM ; Alawa, KA ; Wall, M (ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2022-04-01)
    The Open Perimetry Initiative was formed in 2010 with the aim of reducing barriers to clinical research with visual fields and perimetry. Our two principal tools are the Open Perimetry Interface (OPI) and the visualFields package with analytical tools. Both are fully open source. The OPI package contains a growing number of drivers for commercially available perimeters, head-mounted devices, and virtual reality headsets. The visualFields package contains tools for the analysis and visualization of visual field data, including methods to compute deviation values and probability maps. We introduce a new frontend, the opiApp, that provides tools for customization for visual field testing and can be used as a frontend to run the OPI. The app can be used on the Octopus 900 (Haag-Streit), the Compass (iCare), the AP 7000 (Kowa), and the IMO (CREWT) perimeters, with permission from the device manufacturers. The app can also be used on Android phones with virtual reality headsets via a new driver interface, the PhoneHMD, implemented on the OPI. The use of the tools provided by the OPI library is showcased with a custom static automated perimetry test for the full visual field (up to 50 degrees nasally and 80 degrees temporally) developed with the OPI driver for the Octopus 900 and using visualFields for statistical analysis. With more than 60 citations in clinical and translational science journals, this initiative has contributed significantly to expand research in perimetry. The continued support of researchers, clinicians, and industry are key in transforming perimetry research into an open science.
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    Relating the cortical visual contrast gain response to spectroscopy-measured excitatory and inhibitory metabolites in people who experience migraine
    Chan, YM ; Glarin, R ; Moffat, BA ; Bode, S ; McKendrick, AM ; Lundberg, P (PUBLIC LIBRARY SCIENCE, 2022-01-01)
    OBJECTIVE: This study aimed to determine whether the visual response to flickering checkerboard patterns measured using electroencephalography (EEG) relate to excitatory or inhibitory metabolite levels measured using ultra-high (7Tesla/7T) magnetic resonance spectroscopy (MRS). BACKGROUND: Electrophysiological studies have shown altered visual cortical response amplitudes and contrast gain responses to high contrast flickering patterns in people with migraine. These contrast response anomalies have been argued to represent an imbalance between cortical inhibition and excitation, however the specific mechanism has not been elucidated. METHODS: MRS-measured metabolite levels were obtained from the occipital cortex of 18 participants with migraine and 18 non-headache controls. EEG contrast gain response functions were collected on separate days from a subset of 10 participants with migraine and 12 non-headache controls. Case-control outcome measures were statistically compared between groups both before and after checkboard exposure. RESULTS: No significant difference in GABA and glutamate levels were found between groups nor checkerboard timepoint. Glucose levels were significantly reduced after checkerboard exposure in both participant groups. There was no metabolic signature in visual cortex in response to high-contrast flickering checkboards that distinguished those with migraine and without. There was also no correlation between MRS and EEG measurements in response to the flickering checkerboard. CONCLUSION: Our findings suggest that the mechanisms driving contrast-flickering stimulus aversion are not simplistically reflected by gross changes in metabolic activity in the primary visual cortex.
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    Improved outcomes after implementation of a specialized pediatric cardiac rapid response team
    McKeta, AS ; Hlavacek, AM ; Chowdhury, SM ; Scheurer, M ; Graham, EM ; Zyblewski, SC ; Buckley, JR (CAMBRIDGE UNIV PRESS, 2021-10-01)
    Migraine is a common headache disorder with neurovascular involvement. Because eyecare practitioners are likely to encounter people with migraine in their everyday practice, it is important to understand how migraine might impact on ocular health. In this narrative review, we provide an update on the latest ophthalmic imaging evidence for retinal involvement in migraine, derived from studies of retinal structure and retinal vascular perfusion using spectral domain and swept source optical coherence tomography (OCT) and OCT angiography. Combined structural OCT evidence from a recent meta-analysis indicates subtle and non-specific thinning of the peripapillary retinal nerve fibre layer (RNFL) in people with migraine, whereas there is little consistent evidence for structural abnormalities of the macular region. Recent advances in OCT angiography technology have also provided an opportunity to visualise microstructural damage and vascular dysregulation in the eyes of people with migraine. However, given that OCT and OCT angiography studies have been exclusively cross-sectional, it is not possible to demonstrate the causal effect of migraine events. Furthermore, the lack of common methodology (different ophthalmic imaging devices and analysis algorithms), and very limited datasets (small samples, heterogenous migraine groups), lead to an inability to make strong conclusions regarding the nature of altered retinal structure and vascular perfusion in migraine. Nevertheless, we discuss the clinical implications of such observations for eyecare practitioners and provide practical advice for the monitoring and management of patients with a history of migraine.
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    Neuroplasticity in older adults revealed by temporary occlusion of one eye
    Nguyen, BN ; Malavita, M ; Carter, OL ; McKendrick, AM (ELSEVIER MASSON, CORP OFF, 2021-08-05)
    Occluding one eye for several hours alters visual experience. Specifically, occluding one eye shifts the balance of ocular dominance to favour the recently deprived eye, which can be measured using binocular rivalry. This ocular dominance shift demonstrates homeostatic neuroplasticity within the visual system and has been explored in detail in younger adults. Here we measure whether the strength and general features of neuroplasticity revealed by monocular patching are maintained in older adults. Thirty younger (18-35 years) and 30 older adults (60-81 years) participated. Binocular rivalry features were measured before and after 2 h of occlusion. Post-patching, perceptual dominance of the non-patched eye decreased (p < .001) in both age groups. The effect of occlusion on all features of binocular rivalry did not significantly differ between groups. The older visual system maintains the ability to rapidly adjust to changes in perceptual experience induced by eye occlusion. This preservation of neuroplasticity suggests that visual training methods designed to improve visual performance based on eye occlusion should maintain effectiveness into older age.
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    Normative retrobulbar measurements of the optic nerve using ultra high field magnetic resonance imaging
    Nguyen, BN ; Cleary, JO ; Glarin, R ; Kolbe, SC ; Moffat, BA ; Ordidge, RJ ; Bui, BV ; McKendrick, AM (Association for Research in Vision and Ophthalmology, 2019-07-01)
    Purpose : We exploit the improved spatial resolution and signal-to-noise gain of ultra high field (7T) magnetic resonance imaging (MRI) with a dedicated eye coil for more accurate morphometric measurements of the optic nerve ~2.5mm behind the globe. Methods : Coronal T2-weighted oblique images (TR=2000ms, TE=64ms, FOV=155mm, matrix=384 x 384, slice thickness=0.7mm, scan time=2’34”) through the optic nerve were obtained in 21 healthy adults (20-41 years, 11 emmetropes: +0.75 to -0.50D, 10 myopes: -4.5 to -12D) using a 7T Siemens Magnetom scanner (Erlangen, Germany) and 6-channel eye coil (MRI.TOOLS GmbH, Berlin, Germany). Horizontal and vertical outer diameter of the optic nerve, subarachnoid space (fluid gap) and optic sheath were measured by hand using biomedical imaging software (OsiriX, Pixmeo, Switzerland) (Figure). Significant motion artefacts were avoided with customised fixation and preparation techniques. Results : Horizontal and vertical measurements were similar so were averaged. Right and left eye diameters did not differ and were highly correlated (optic nerve: Pearson r=0.9, p<0.001; fluid gap: r=0.8, p<0.001; optic sheath: r=0.7, p<0.001); hence we report left eye data only. Optic nerve diameter (average of horizontal and vertical diameters) ranged from 2.8-4.1mm in emmetropes and 1.5-4.2mm in myopes and correlated with refractive error (Spearman r=0.46, p=0.04). Similarly, fluid gap diameter (emmetropes: 3.6-5.5mm, myopes: 2.5-5.6mm), but not optic sheath diameter (emmetropes: 4.5-6.8mm, myopes: 4.2-6.8mm), correlated with refractive error (r=0.47, p=0.03). Conclusions : Ultra high field MRI with thinner slices enables more accurate demarcation of the optic nerve, surrounding fluid/subarachnoid space and optic sheath without overlapping of neighbouring anatomy (minimal partial volume artefact). Our 7T MRI-derived normative measurements of optic nerve, fluid gap and sheath diameter are comparable with published reports in healthy observers obtained at conventional MRI magnetic fields (1.5-3T). Our findings suggest a trend for retrobulbar optic nerve and subarachnoid space, but not optic sheath, to be smaller in high myopes.
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    Motion perception at mesopic light levels: effects of physiological ageing and eccentricity
    Sepulveda, JA ; Anderson, AJ ; Wood, JM ; McKendrick, AM (WILEY, 2021-01-24)
    PURPOSE: To explore the differential effects of age and eccentricity on the perception of motion at photopic and mesopic light levels. METHODS: Thirty-six visually normal participants (18 younger; mean age 25 years, range: 20-31) and (18 older; mean age 70 years, range: 60-79) underwent two testing sessions, one at photopic and one at mesopic light levels. In each session, motion perception was tested binocularly at two eccentricities (centrally, and peripherally at 15° rightwards and 5° superior to the horizontal) for four motion tasks: minimum contrast of a drifting Gabor to identify motion direction (motion contrast); translational global motion coherence; biological motion embedded in noise and the minimum duration of a high-contrast Gabor to determine the direction of motion, using two Gabor sizes to measure spatial surround suppression of motion. RESULTS: There was a significant main effect of light condition (higher thresholds in mesopic) for motion contrast (p < 0.001), translational global motion (p = 0.001) and biological motion (p < 0.001); a significant main effect of age (higher thresholds in older adults) for motion contrast (p < 0.001) and biological motion (p = 0.04) and a significant main effect of eccentricity (higher thresholds peripherally) for motion contrast (p < 0.001) and biological motion (p < 0.001). Additionally, we found a significant three-way interaction between light levels, age and eccentricity for translational global motion (similar increase in mesopic thresholds centrally for both groups, but a much larger deterioration in older adult's peripheral mesopic thresholds, p = 0.02). Finally, we found a two-way interaction between light condition and eccentricity for translational global motion (higher values in central mesopic relative to peripheral photopic, p = 0.001) and for biological motion (higher values in peripheral mesopic relative to central photopic, p < 0.001). CONCLUSIONS: For the majority of tasks assessed, motion perception was reduced in mesopic relative to photopic conditions, to a similar extent in both age groups. However, because some older adults exhibited elevated thresholds even under photopic conditions, particularly in the periphery, the ability to detect mesopic moving stimuli even at high contrast was markedly impaired in some individuals. Our results imply age-related differences in the detection of peripheral moving stimuli at night that might impact hazard avoidance and night driving ability.