Imaging of the eye shows individual differences in the shape of the macula

One of our major research areas is in the field of glaucoma, an eye disease that affects the retinal ganglion cells (nerve cells). These cells are most densely located within the central 10° of the retina from the very centre, the region which is called the macula. Recently there has been an increased interest in the study of the morphology (shape) and functionality of the macula in people suffering from glaucoma, because we expect that this is where the initial pathological changes would appear.

Many researchers have tried to connect functional changes with morphological changes within the central 10° of the retina in people with glaucoma by creating a ‘structure-function map’. In particular, some researchers have included individual anatomical information to improve these maps. For example, at the very centre (foveola), one photoreceptor (the light-sensitive cell of the retina) connects to approximately one retinal ganglion cell, but the connection is slightly displaced spatially. Correcting for this factor would be unnecessary, however, if the maculae of all eyes were equal.

In this paper we explored whether some macular parameters such as the maximum thickness, the minimum thickness and the horizontal distance from the two previous values (we call it “radius”) of high-resolution optical coherence tomography (OCT) scans centered at the foveola are different between individuals. The figure below shows where the scans are centred.

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Retinal photo showing where the scans are taken (at the very centre of the retina, the fovea)

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The three parameters compared: central thickness, maximum thickness (height) and radius.

We found that the measured foveal shape parameters are different between different people. We also found that the foveal shape is not symmetrical between superior and inferior parts of the retina, which is important because the damage is often asymmetric between the superior and inferior hemiretinae in glaucoma.

This work formed part of Juan Sepulveda’s Masters project. You can read the full published article in Investigative Ophthalmology and Visual Science here.

New paper: Automatic identification of the temporal raphe from standard retinal scans

Glaucoma is a disease of the optic nerve. The nerve fibres that travel along the optic nerve to the brain are spread out across the retina, and can be visualised using an imaging technique called  optical coherence tomography (OCT). Individual nerve fibre bundles cannot be seen with standard clinical tests. It is typically assumed that if a nerve fibre bundle is lost in one part of the retina, then a person will have corresponding visual loss in that part of their field of view (i.e. visual field). Recently it has been recognised that different people can have quite different distributions of retinal nerve fibres, which means that the relationship between the location of loss of visual field and the location of nerve fibre damage differs between individuals and can be hard to predict.

Our lab has recently developed sophisticated models that overcome this problem to predict just how a particular nerve fibre pattern should map onto an individual patient’s visual field. These models depend critically upon a single measured parameter from the patient’s eye, namely the axis of symmetry between fibres that travel along the upper (superior) retina and those that travel along the lower (inferior) retina. This axis is known as the temporal nerve fibre raphe or temporal raphe for short (shown in the figure below as a red line).

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Figure 1. The temporal raphe (red), where the nerve fibres travelling from the upper and lower retina meet, can be identified using retinal scans

The location of the temporal raphe is typically difficult to appreciate with standard imaging techniques. However, it has been shown recently that by collecting OCT data with scans of very high spatial density, the raphe can be visualised in exquisite detail and its orientation hence measured very precisely. Unfortunately, collection of such data requires a lot of time, good image quality, and particularly steady fixation, which are luxuries that we do not have in a clinical setting.

In this paper we set out to determine just how well the temporal raphe can be determined from standard scans acquired routinely in the clinic (‘macular cube’ scans). By acquiring additional high density scan data on the same eyes, we were able to measure how accurately several automated algorithms can estimate the orientation of the temporal raphe. Our results show that the best performing algorithm gave a mean error of 1.5°. The ability to quantify the orientation of the raphe with this level of precision paves the way for future work that uses these measurements to accurately map retinal structure (by OCT) to retinal function (by visual field), in order to more accurately assess the health of the retina and optic nerve in glaucoma.

This paper has been published in Biomedical Optics Express and is available to read here.

A trip to Italy: Imaging and Perimetry Society Symposium

Members of our lab have just returned from a trip to sunny Italy to attend the 22nd International Visual Field Imaging Symposium. The meeting was held in the small town of Udine, in north east Italy, with the conference itself being held in the Castle of Udine.

Nikki presented a talk “Incorporating probabilistic graphical models into perimetric test procedures”, which describes work directly from her PhD studies.

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Allison was busy with her role as Secretary of the Imaging and Perimetry Society  which is an international organisation of researchers that aims to: 1) to promote the study of normal and abnormal visual function and of ocular imaging, and  2) to ensure and facilitate the cooperation and friendship of scientists of different countries working and interested in these disciplines. The next IPS meeting (23rd International Visual Field and Imaging Symposium) will be held in Kanazawa, Japan, May 9-12, 2018.

Lab adventures down the Great Ocean Road

On a winter’s weekend in August, our lab went on a roadtrip down the Great Ocean Road. Our main activity was to walk along part of the Great Ocean Walk from Blanket Bay campground to the Cape Otway lighthouse. Highlights from the trip were:

  • Koala spotting in the Cape Otway National Park
  • Friendly alpacas (and ‘cowpacas’) on the drive out from the lighthouse
  • Hearty bowls of pasta arabbiata and board games
  • Barefoot leaps across the chilly water to reach the hidden cove of Parker’s Inlet
  • Marine mammal spotting from Apollo Bay and the Cape Otway lighthouse
  • Free French lessons from our visiting PhD student from Lille, Clement
  • Quick detour on the drive home to the Erskine Falls outside of Lorne
  • Our very own resident paparazzo (Honours student, Chongyue) taking photos of our every move

 

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Our enthusiastic bunch before we embarked on the 11.5 km walk

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Halfway stop at Parker’s Inlet between Blanket Bay and Cape Otway lighthouse

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We made it to the Cape Otway lighthouse!

Recent conference presentations from our lab

Members of our lab have been busy attending national and international conferences this year to showcase the wide research interests of our laboratory and gain useful feedback from our scientific colleagues.

Experimental Psychology Conference (EPC)

The Australian Society for Experimental Psychology (ASEP) hosts the Experimental Psychology Conference annually and this year it was held at the University of Melbourne from 30th of March to 2nd of April. Members from our lab presented posters (Menaka and Janet) and gave oral presentations (Allison and Bao). This was a great opportunity for them to share their new research work with a wide spectrum of people.

Menaka explored the effect of ageing and attention on two visual phenomena, namely visual crowding and surround suppression of perceived contrast in peripheral vision. It was found that surround suppression is increased in older adults when tested in the visual periphery whereas visual crowding remains unchanged. Further, attentional aspects did not correlate with crowding or surround suppression.

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Menaka with Professor David Badcock at the Experimental Psychology Conference, Melbourne. Her poster was titled ‘The effect of ageing and attention on visual crowding and surround suppression of perceived contrast

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Janet explains her poster titled ‘Neural correlations of audiovisual synchrony judgements in older adults‘ at the Experimental Psychology Conference, Melbourne

 

Meeting for the Association for Research in Vision and Ophthalmology (ARVO)

ARVO is the biggest international conference in vision science and ophthalmology and attracts over 9000 delegates. This year it was held in May in Seattle. Members from our lab who presented were Allison, Andrew, Fumi and our recent PhD graduates Shonraj and Luke.

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Fumi presented a poster at ARVO in Seattle titled ‘The relationship between retinal vessels and retinal nerve fiber trajectories in the temporal retina’

Meeting for the Vision Sciences Society (VSS)

The Vision Sciences Society meeting was held in May in St Pete’s beach in sunny Florida. Current PhD student Kabi presented a poster titled “Foveal center surround contrast suppression reveals differential effect of aging on intraocular and interocular suppression”.

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Kabi explains his poster at the Vision Sciences Society conference in Florida

Asia Pacific Conference on Vision (APCV)

Allison, Astrid, Bao and Janet flew to Western Australia for the 12th Annual Asia Pacific Conference on Vision (14-17th July) in Fremantle. Researchers came from 14 different countries, with keynote presentations from Shinya Nishida (Japan), Concetta Morrone (Italy), and Shaun Collin (UWA).

Bao presented recently published work (‘Normal ageing affects visual contextual effects of orientation, contrast, flicker and luminance’) that was described in our previous lab blog post here.

Janet presented recent findings from a collaborative project with researchers at the Royal Melbourne Hospital on an atypical condition known as visual snow. People with visual snow experience ongoing static in their vision even when they close their eyes – much like looking at a poorly tuned analogue TV. The project is using a range of behavioural tasks of vision that assess the balance between excitation and inhibition in the visual system.

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Allison, Bao, Astrid and Janet presented at the 12th Annual Asia Pacific Conference on Vision in Fremantle, Western Australia

New article in Frontiers in Aging Neuroscience

We are interested in how our perception of visual stimuli can be altered by presenting the stimuli of interest against a different background or context. For example, we have previously demonstrated contextual effects on contrast –  where the contrast of a pattern appears to be less than its physical contrast when surrounded by a similar pattern but of higher contrast. Similar contextual effects are also seen when we test other fundamental visual features, such as luminance (brightness), orientation (tilt) and flicker. For example, a grey patch appears darker when placed on a bright background, and vice versa (also known as the ‘simultaneous brightness illusion’, see figure below).

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Example ‘illusion’ of brightness (luminance) where the context in which a visual stimulus is presented can markedly alters its appearance. The two grey squares in the middle of each panel are the same physical brightness, but they appear to be (A) brighter when placed against a dark background, and (B) darker when placed against a light background.

Some contextual effects (e.g. contrast) have been studied extensively in younger and older observers to understand how normal, healthy ageing affects our visual perception. For the first time, we have tested a range of contextual effects (luminance, contrast, flicker and orientation) in the same observers to investigate whether the healthy ageing process results in consistent or selective alterations to visual perception. Performance on these contextual tasks is highly relevant to real-world functioning where objects of interest are rarely presented on uniform backgrounds in isolation. We find that in older adults, relative to younger adults, perceptual judgements about the luminance, contrast, depth of flicker and orientation of a visual stimulus are more strongly affected when non-uniform backgrounds are introduced. However, the strength of contextual effect on one task does not necessarily predict performance on all other tasks, which suggests that there is not one single, unifying mechanism for the range of contextual effects observed.

You can read the full version of the paper in Frontiers in Aging Neuroscience here.

SWeLZ – a new algorithm for measuring visual field loss

Glaucoma is the leading cause of irreversible blindness globally. Glaucomatous vision loss occurs in the peripheral visual field (areas of vision other than where you are directly looking). A major theme of our laboratory’s work is to design new algorithms to more efficiently measure a person’s visual field sensitivity, which is an important part of detecting and managing the disease.

Our most recent algorithm, SWeLZ, appeared in print earlier this month in TVST (Translational Vision Science and Technology). The algorithm was tested using computer simulations of patient responses. The simulations suggest that SWeLZ can significantly speed up testing times by approximately 25% in people without visual field loss or those with very early visual field loss, while still being able to detect glaucoma.

You can download a copy of the published article here.

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Janet having her visual field sensitivity measured