National Vision Research Institute

Carlton, Australia

National Vision Research Institute

Carlton, Australia

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Williams E.D.,Monash University | Williams E.D.,Imperial College London | Magliano D.J.,Baker IDI Heart and Diabetes Institute | Tapp R.J.,National Vision Research Institute | And 2 more authors.
Annals of Behavioral Medicine | Year: 2013

Background: The evidence supporting a relationship between stress and diabetes has been inconsistent. Purpose: This study examined the effects of stress on abnormal glucose metabolism, using a population-based sample of 3,759, with normoglycemia at baseline, from the Australian Diabetes, Obesity and Lifestyle study. Methods: Perceived stress and stressful life events were measured at baseline, with health behavior and anthropometric information also collected. Oral glucose tolerance tests were undertaken at baseline and 5-year follow-up. The primary outcome was the development of abnormal glucose metabolism (impaired fasting glucose, impaired glucose tolerance, and type 2 diabetes), according to WHO 1999 criteria. Results: Perceived stress predicted incident abnormal glucose metabolism in women but not men, after multivariate adjustment. Life events showed an inconsistent relationship with abnormal glucose metabolism. Conclusions: Perceived stress predicted abnormal glucose metabolism in women. Healthcare professionals should consider psychosocial adversity when assessing risk factor profiles for the development of diabetes. © 2013 The Society of Behavioral Medicine.

Williams E.D.,Monash University | Rawal L.,Monash University | Oldenburg B.F.,Monash University | Renwick C.,Monash University | And 2 more authors.
Diabetes Care | Year: 2012

OBJECTIVE - There is an established link between health-related functioning (HRF) and cardiovascular disease (CVD) mortality, and it is known that those with diabetes predominantly die of CVD. However, few studies have determined the combined impact of diabetes and impaired HRF on CVD mortality. We investigated whether this combination carries a higher CVD risk than either component alone. RESEARCH DESIGN AND METHODS - The Australian Diabetes, Obesity and Lifestyle (AusDiab) study included 11,247 adults aged ≥25 years from 42 randomly selected areas of Australia. At baseline (1999-2000), diabetes status was defined using the World Health Organization criteria and HRF was assessed using the SF-36 questionnaire. RESULTS - Overall, after 7.4 years of follow-up, 57 persons with diabetes and 105 without diabetes had died from CVD. In individuals with and without diabetes, HRF measures were significant predictors of increased CVD mortality. The CVD mortality risks among those with diabetes or impaired physical health component summary (PCS) alone were similar (diabetes only: hazard ratio 1.4 [95% CI 0.7-2.7]; impaired PCS alone: 1.5 [1.0-2.4]), while those with both diabetes and impaired PCS had a much higher CVD mortality (2.8 [1.6-4.7]) compared with those without diabetes and normal PCS (after adjustment for multiple covariates). Similar results were found for the mental health component summary. CONCLUSIONS - This study demonstrates that the combination of diabetes and impaired HRF is associated with substantially higher CVD mortality. This suggests that, among those with diabetes, impaired HRF is likely to be important in the identification of individuals at increased risk of CVD mortality. © 2012 by the American Diabetes Association.

Bhagavatula P.S.,Australian National University | Bhagavatula P.S.,University of Queensland | Bhagavatula P.S.,National Vision Research Institute | Claudianos C.,University of Queensland | And 5 more authors.
Current Biology | Year: 2011

Although considerable effort has been devoted to investigating how birds migrate over large distances, surprisingly little is known about how they tackle so successfully the moment-to-moment challenges of rapid flight through cluttered environments [1]. It has been suggested that birds detect and avoid obstacles [2] and control landing maneuvers [3-5] by using cues derived from the image motion that is generated in the eyes during flight. Here we investigate the ability of budgerigars to fly through narrow passages in a collision-free manner, by filming their trajectories during flight in a corridor where the walls are decorated with various visual patterns. The results demonstrate, unequivocally and for the first time, that birds negotiate narrow gaps safely by balancing the speeds of image motion that are experienced by the two eyes and that the speed of flight is regulated by monitoring the speed of image motion that is experienced by the two eyes. These findings have close parallels with those previously reported for flying insects [6-13], suggesting that some principles of visual guidance may be shared by all diurnal, flying animals. © 2011 Elsevier Ltd. All rights reserved.

Solomon S.G.,University of Sydney | Tailby C.,University of Sydney | Tailby C.,National Vision Research Institute | Cheong S.K.,National Vision Research Institute | Camp A.J.,University of Sydney
Journal of Neurophysiology | Year: 2010

Several parallel pathways convey retinal signals to the visual cortex of primates. The signals of the parvocellular (P) and magnocellular (M) pathways are well characterized; the properties of other rarely encountered cell types are distinctive in many ways, but it is not clear that they can provide signals with the same fidelity. Here we study this by characterizing the temporal receptive field of neurons in the lateral geniculate nucleus of anesthetized marmosets. For each neuron, we measured the response to a flickering uniform field, and, from this, estimated the linear and nonlinear receptive fields using spike-triggered average (STA) and spike-triggered covariance (STC) analyses. As expected the response of most P-cells was dominated by the STA, but the response of most M-cells required additional nonlinear components, and these usually acted to suppress cell responses. The STC analysis showed stronger suppressive axes in suppressed-by-contrast cells, and both suppressive and excitatory axes in ON-OFF cells. Together, the STA and the STC analyses form a model of the temporal response to a large uniform field: under this model, the information that was provided by suppressed-by-contrast cells or ON-OFF cells approached that provided by the P- and M-cells. However, whereas Pand M-cells provided more information about luminance, the nonlinear cells provided more information about the contrast energy. This suggests that the nonlinear cells provide complimentary signals to those of P- and M-cells, with reasonably high fidelity, and may play an important role in normal visual processing. Copyright © 2010 The American Physiological Society.

Wong R.C.S.,Australian National University | Wong R.C.S.,National Vision Research Institute | Cloherty S.L.,Australian National University | Cloherty S.L.,National Vision Research Institute | And 6 more authors.
Journal of Neurophysiology | Year: 2012

Mammalian retina contains 15-20 different retinal ganglion cell (RGC) types, each of which is responsible for encoding different aspects of the visual scene. The encoding is defined by a combination of RGC synaptic inputs, the neurotransmitter systems used, and their intrinsic physiological properties. Each cell's intrinsic properties are defined by its morphology and membrane characteristics, including the complement and localization of the ion channels expressed. In this study, we examined the hypothesis that the intrinsic properties of individual RGC types are conserved among mammalian species. To do so, we measured the intrinsic properties of 16 morphologically defined rat RGC types and compared these data with cat RGC types. Our data demonstrate that in the rat different morphologically defined RGC types have distinct patterns of intrinsic properties. Variation in these properties across cell types was comparable to that found for cat RGC types. When presumed morphological homologs in rat and cat retina were compared directly, some RGC types had very similar properties. The rat A2 cell exhibited patterns of intrinsic properties nearly identical to the cat alpha cell. In contrast, rat D2 cells (ON-OFF directionally selective) had a very different pattern of intrinsic properties than the cat iota cell. Our data suggest that the intrinsic properties of RGCs with similar morphology and suspected visual function may be subject to variation due to the behavioral needs of the species. © 2012 the American Physiological Society.

Hietanen M.A.,National Vision Research Institute | Hietanen M.A.,University of Melbourne
Vision Research | Year: 2015

The perception of speed is dependent on the history of previously presented speeds. Adaptation to a given speed regularly results in a reduction of perceived speed and an increase in speed discriminability and in certain circumstances can result in an increase in perceived speed. In order to determine the relative contributions of the local and global speed components on perceived speed, this experiment used expanding dot flow fields with accelerating (global), decelerating (global) and mixed accelerating/decelerating (local) speed patterns. Profound decreases in perceived speed are found when viewing low test speeds after adaptation to high speeds. Small increases in the perceived speed of high test speeds occur following adaptation to low speeds. There were small but significant differences in perceived stimulus speed after adaptation due to different acceleration profiles. No evidence for global modulation of speed discriminability following adaptation was found. © 2015 Elsevier Ltd.

Bui B.V.,University of Melbourne | Batcha A.H.,National Vision Research Institute | Batcha A.H.,University of Melbourne | Fletcher E.,University of Melbourne | And 2 more authors.
PLoS ONE | Year: 2013

Purpose:To determine relationship between the magnitude of intraocular pressure (IOP) during a fixed-duration episode of acute elevation and the loss of retinal function and structure 4 weeks later in rats.Methods:Unilateral elevation of IOP (105 minutes) was achieved manometrically in adult Brown Norway rats (9 groups; n = 4 to 8 each, 10-100 mm Hg and sham control). Full-field ERGs were recorded simultaneously from treated and control eyes 4 weeks after IOP elevation. Scotopic ERG stimuli were white flashes (-6.04 to 2.72 log cd.s.m-2). Photopic ERGs were recorded (1.22 to 2.72 log cd.s.m-2) after 15 min of light adaptation (150 cd/m2). Relative amplitude (treated/control, %) of ERG components versus IOP was described with a cummulative normal function. Retinal ganglion cell (RGC) layer density was determined post mortem by histology.Results:All ERG components failed to recover completely normal amplitudes by 4 weeks after the insult if IOP was 70 mmHg or greater during the episode. There was no ERG recovery at all if IOP was 100 mmHg. Outer retinal (photoreceptor) function demonstrated the least sensitivity to prior acute IOP elevation. ERG components reflecting inner retinal function were correlated with post mortem RGC layer density.Conclusions:Retinal function recovers after IOP normalization, such that it requires a level of acute IOP elevation approximately 10 mmHg higher to cause a pattern of permanent dysfunction similar to that observed during the acute event. There is a 'threshold' for permanent retinal functional loss in the rat at an IOP between 60 and 70 mmHg if sustained for 105 minutes or more. © 2013 Bui et al.

Cloherty S.L.,National Vision Research Institute | Cloherty S.L.,University of Melbourne | Ibbotson M.R.,National Vision Research Institute | Ibbotson M.R.,University of Melbourne
Journal of Neurophysiology | Year: 2015

Some neurons in early visual cortex are highly selective for the position of oriented edges in their receptive fields (simple cells), whereas others are largely position insensitive (complex cells). These characteristics are reflected in their sensitivity to the spatial phase of moving sine-wave gratings: simple cell responses oscillate at the fundamental frequency of the stimulus, whereas this is less so for complex cells. In primates, when assessed at high stimulus contrast, simple cells and complex cells are roughly equally represented in the first visual cortical area, V1, whereas in the second visual area, V2, the majority of cells are complex. Recent evidence has shown that phase sensitivity of complex cells is contrast dependent. This has led to speculation that reduced contrast may lead to changes in the spatial structure of receptive fields, perhaps due to changes in how feedforward and recurrent signals interact. Given the substantial interconnections between V1 and V2 and recent evidence for the emergence of unique functional capacity in V2, we assess the relationship between contrast and phase sensitivity in the two brain regions. We show that a substantial proportion of complex cells in macaque V1 exhibit significant increases in phase sensitivity at low contrast, whereas this is rarely observed in V2.Our results support a degree of hierarchical processing from V1 to V2 with the differences possibly relating to the fact that V1 combines both subcortical and cortical input, whereas V2 receives input purely from cortical circuits. © 2015 the American Physiological Society.

Hung Y.-S.,National Vision Research Institute | Hung Y.-S.,University of Melbourne | Ibbotson M.R.,National Vision Research Institute | Ibbotson M.R.,University of Melbourne
Frontiers in Neuroanatomy | Year: 2014

Honeybees have a visual system composed of three ocelli (simple eyes) located on the top of the head, in addition to two large compound eyes. Although experiments have been conducted to investigate the role of the ocelli within the visual system, their optical characteristics, and function remain controversial. In this study, we created three-dimensional (3-D) reconstructions of the honeybee ocelli, conducted optical measurements and filled ocellar descending neurons to assist in determining the role of ocelli in honeybees. In both the median and lateral ocelli, the ocellar retinas can be divided into dorsal and ventral parts. Using the 3-D model we were able to assess the viewing angles of the retinas. The dorsal retinas view the horizon while the ventral retinas view the sky, suggesting quite different roles in attitude control. We used the hanging drop technique to assess the spatial resolution of the retinas. The lateral ocelli have significantly higher spatial resolution compared to the median ocellus. In addition, we established which ocellar retinas provide the input to five pairs of large ocellar descending neurons. We found that four of the neuron pairs have their dendritic fields in the dorsal retinas of the lateral ocelli, while the fifth has fine dendrites in the ventral retina. One of the neuron pairs also sends very fine dendrites into the border region between the dorsal and ventral retinas of the median ocellus. © 2014 Hung and Ibbotson.

Cloherty S.L.,National Vision Research Institute
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2012

In this paper we aim to quantify the effect of the inner limiting membrane (ILM) of the retina on the thresholds for epiretinal electrical stimulation of retinal ganglion cells by a microelectronic retinal prosthesis. A pair of bipolar stimulating electrodes was placed either above (on the epiretinal surface) or below the ILM while we made whole-cell patch-clamp recordings from retinal ganglion cells in an isolated rat retinal whole-mount preparation. Across our cell population we found no significant difference in the median threshold stimulus amplitudes when the stimulating electrodes were placed below as opposed to above the ILM (p = 0.08). However, threshold stimulus amplitudes did tend to be lower when the stimulating electrodes were placed below the ILM (30 μA vs 56 μA).

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