Visual field test | EPFL Graph Search

A visual field test is an eye examination that can detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits. Visual field testing can be performed clinically by keeping the subject's gaze fixed while presenting objects at various places within their visual field. Simple manual equipment can be used such as in the tangent screen test or the Amsler grid. When dedicated machinery is used it is called a perimeter. The exam may be performed by a technician in one of several ways. The test may be performed by a technician directly, with the assistance of a machine, or completely by an automated machine. Machine-based tests aid diagnostics by allowing a detailed printout of the patient's visual field. Other names for this test may include perimetry, Tangent screen exam, Automated perimetry exam or Goldmann visual field exam. Examination methods

A sensitivity analysis on glare detection parameters

Marilyne Andersen, Yiyuan Jia, Mandana Sarey Khanie, Jan Wienold

Maximizing daylight access while maintaining a glare-free indoor environment is an ongoing challenge for daylighting design. Glare is a discomfort sensation that is produced as a result of greater variation of luminance across the visual field than the one that the eye is adapted to. This type of discomfort sensation is one of the main drivers for building users' interaction with the façcade setting, which consequently can change the building's performance over time. Optimised integration of glare-free daylight solutions thus proves to be crucial for a sustainable building design. The existing methods for glare-free daylighting design rely on analyses on image-based advanced renderings with accurate simulation of light behaviour. These methods are becoming more commonly used for daylighting design using simulated three-dimensional geometrical model of the architectural space and employing tools such as Radaince for rendering the light. As convenient as this approach seems, it has complexities in attempts to define different components of the visual comfort metrics. One of these complexities is detecting the glary image pixels. The existing glare source detection methods consider any image pixel of luminance value that is x-times larger than the average luminance of a visual adaptation region as a potential glare source pixel. The method then searches the image based on a predefined search radius to find and combine all the glary pixels as one glare source. In this method, the value of the threshold multiplier and the search radius are decided intuitively based on the luminous environment of the studied scene. In this study we have made a sensitivity analysis on the threshold and search radius parameters for glare source pixels detection.

2014

Investigation of electrical stimulation of the optic nerve for artificial vision

Vivien Gaillet

Thanks to recent technological advances in microelectronics and bioengineering, it is now possible to restore lost or impaired sensory modalities by interfering the nervous system with elec-tronic devices and artificially reproducing the electrical encoding of the neural signals of the missing or defective sensory organs or tissues, as evidenced by the successful development of cochlear im-plants allow the restoration of hearing in deaf patients. This makes the treatment of blindness, a very impairing condition that significantly decreases the quality of life of the person it affects, a plausible possibility today, and many groups are currently attempting to apply the same principle of cochlear implants to sight restoration. So far, the preferred approach has been retinal implants due to their proximity to the defective cells, the photoreceptors, which minimizes the amount of processing of the neural signal that needs to be reproduced, and due to the reasonable number of stimulating sites that the retina can accommodate. Several devices have already demonstrated the possibility of restor-ing some degree of functional vision, albeit still very rudimentary. However, unlike hearing, vision is an extremely complex sensory modality, involving several cell types forming elaborate circuitry, which makes the advantages of retinal implants less definitive, and other alternative approaches such as op-tic nerve of cortical prosthesis still worth exploring. We believe the optic nerve stimulation is an at-tractive approach for several reasons; firstly, it does not require optical transparency. Secondly, it can address specific conditions such as severe eye trauma or retinal detachment where retinal implants cannot be employed. Finally, thanks to the organization of the optic nerve axonal fibers, it may likely result in the activation of axons originating from the same region of the visual field. This is not the case with epiretinal implants, which have been reported to stimulate undesired axons of passage in addition to the somas of their cellular targets, resulting in curved and elongated phosphenes that lim-it the implant's achievable resolution. In this thesis, we introduce a novel intraneural electrode design, the OpticSELINE, which aims at im-proving the selectivity and stability of the extra-neural cuff-electrodes previously used in optic nerve stimulation. We first characterized the device's improved mechanical and electrical properties and then proceeded to evaluate its stimulation capacity in vivo in the rabbit. In parallel to demonstrating the ability to modulate the magnitude of the cortical activation through the increase or decrease of the stimulation current, we implemented a hybrid finite element computational model to estimate the dimensions of the nerve portions activated by our electrical stimulation protocols. Using inde-pendent component analysis (ICA), we also developed a workflow that allows isolating components of the signal selectively related to a single or a pair of stimulating electrodes. We then focused on the development of new and improved algorithms to analyze the cortical activation patterns. We first developed a support machine vector (SVM)-based classifier that allowed us to accurately identify both the visual stimulus or the stimulating electrode that elicited a given cortical activation pattern amongst ten and eight total potential stimuli. Finally, we developed a regression model that also al-lowed us to accurat

EPFL2021

Photovoltaic stimulation of retinal microcircuit for vision restoration

Naïg Aurelia Ludmilla Chenais

Sight restoration through retinal prostheses was still a mere dream a century ago. Current challenges are even greater: providing a quantitatively and qualitatively useful artificial vision to late blind patients. Existing approaches all face engineering and biological questions which directly threaten the quality of the restored vision. Compromises made on stiff materials or external powering restrain the restored visual field and the stimulation resolution. Epiretinal implants are large but offer limited resolution, and stimulate retinal ganglion cell non-specifically through multiple compartments, including distal axons. Subretinal and suprachoroidal implants are limited in size but rely on inner retina activation: it allows to preserve most of spatial and temporal properties of the sighted response, but neurons' responsivity rapidly wanes. Axonal activation and desensitization hamper the spatiotemporal properties of the perceived phosphenes. High-level perceptual mechanisms can resolve the missing piece of information, but require a high cognitive load: a too high price to pay for implants recipients to adapt and use artificial vision on day to day life. Current visual prostheses do not rescue vision as a primary sense in implanted patients. A 20/200 visual acuity, together with a 30 to 40° visual field and qualitative properties as close as possible to patients' early visual experience are the minimal requirements for a useful prosthetic approach. The introduction of light-powered electronics represents a step forward in biomimetic retinal activation, but it is not fully emancipated from power supply and limited coverage concerns. The use of organic semiconductors allows to fabricate flexible p-n junctions that can be embedded into a large hemispherical epiretinal implant. Such a photovoltaic array can cover 45° of visual angle, and total up to 10'498 pixels. Complementary to this high-density and wide-field implant engineering, investigations on retinal network activation allow to design network-oriented photovoltaic stimulation paradigms. Strategies that factor the intrinsic connectivity and properties of retinal neurons - convergence, lateral inhibition and adaptation mechanisms - permit to take advantage of the retinal microcircuit organization. A wide-field photovoltaic epiretinal approach could restore peripheric vision with native visual acuity in Retinitis Pigmentosa patients, as well as a theoretical 20/480 foveal visual acuity. The high resolution of the stimulation has been electrophysiologically evaluated in-vitro; photovoltaic stimulation of degenerating mouse retinas revealed that the non-rectangular photovoltage delivered under 560 nm illumination was prone to recruit inner excitatory and inhibitory circuits from the epiretinal side. This allows first to avoid uncontrolled axonal stimulation of retinal ganglion cells, second to preserve the intrinsic processing, and third to benefit from natural lateral response segregation. In addition, delivering light stimuli in a non-stationary manner that micmics fixational saccades allows to reduce neurons' desensitization. The proposed approach, that combines withstanding organic photovoltaic prosthesis, and naturalistic epiretinal stimulation paradigm, could allow to stimulate human parasol cells with a natural spatial resolution and limit the need of head scanning. Both points are critical for motion perception, self-orientation and ambulation in late blind patients.

EPFL2021

Investigation of electrical stimulation of the optic nerve for artificial vision

Vivien Gaillet

EPFL2021

Photovoltaic stimulation of retinal microcircuit for vision restoration

Naïg Aurelia Ludmilla Chenais

EPFL2021