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Our Mission
Restore | Retrain | Rehabilitate
Restore | Retrain | Rehabilitate
In this lab, we are interested in assessing and enhancing the functional visual abilities of individuals with ultra-low vision. We also use psychophysical experiments to investigate innovative methods for improving visual prostheses.
Retinal Prosthesis
These studies are clinical trials that measures the safety and functionality of the retinal prosthesis device using psychophysical experiments. The Argus II is a retinal prosthetic device that was approved in 2013 by the USFDA as a Humanitarian Use device for end-stage retinitis pigmentosa. The Argus II system provides electrical stimulation of secondary nerve cells in the retina to induce visual perception in blind individuals with retinitis pigmentosa (RP). Since the start of the first clinical trial in 2007, it has been implanted in more than 300 patients worldwide. The Argus II has a 10 x 6 electrode array that provides stimulation from representing frames coming from a head-mounted camera. The stimulation is presented as 4 – 8 intensity levels representing the brightness range of the image. These studies are carried out in collaboration with Second Sight Medical Products company and clinical centers in multiple countries.
In these projects, we aim to learn how Argus II wearers use their implant, and how to further improve the benefits to the user either by adjusting functions performed by the Video Processing Unit (VPU), or by modifying the image that the VPU receives from the camera.
Prosthetic Low Vision Rehabilitation
(PLoVR) study
The goal of this study is to create, refine and integrate tools for assessment and rehabilitation of individuals with ultra-low vision (ULV). This is done by developing a visual functioning questionnaire (VFQ) and performance measures for activities of daily living (ADL) in an ultra-low vision population. There are several versions of the ULV-VFQ [Dagnelie, G. et al. 2017c], with 150 and 50 items used most frequently. The questionnaire items were developed from ultra-low vision patients’ description how they use their remaining vision.
Furthermore, these questionnaire items are going to be enhanced by analyzing the performance of patients in a real word situation of specific tasks that are presented in the ULV-VFQ. Also, the assessment of patients using native vision and recipients of BrainPort, Argus II retinal implant and/or other sight treatment, are going to be compared and analyzed. Results from this study are particularly important in prosthetic and vision restoring therapies, to evaluate, train and track outcomes as well as measure functional effectiveness of a treatment.
This is a multi-center project in collaboration of Wilmer eye institute , the Chicago Light House and the Center for the Blind and Visually Impaired in Utica to cover a large population of the patients with ULV as well as recipients of sight treatments including vision aids and prosthesis.
Intra-Cortical Visual Prosthesis
Cortical implants consist of one or more sets of electrode arrays that similar to the retina implants, provides the stimulation based on the head mounted camera input. The cortical implant has a great potential to target a broader range of blindness, including from glaucoma or optic nerve trauma. Also, there is a possibility to achieve better resolution and/or wider field of view with stimulation of primary visual cortex areas.
The intracortical visual prosthesis (ICVP) is being developed by collaboration of University of Chicago, University of Texas Dallas, University of Alberta and Illinois Institute of Technology as well as many small companies, with sponsorship under the federal BRAIN initiative, through the National Institute for Neurological Disorders and Stroke (NINDS) [http://neural.iit.edu/research/icvp/]. The initial implantation is scheduled for the Fall of 2019.
Here at Hopkins, we aim to prepare for the testing that will begin as soon as the first ICVP implantations have been performed. There are two main objectives for these tests. First, we are going to study the phosphene maps that allows stimulation of the right electrodes to make patients see the images with minimal distortion. Second, we are going to test how well ICVP recipients can recognize and grasp objects, and how well they find their way to move around in a controlled environment.
Ultra Low Vision
Ultra Low Vision
Rationale
Rationale
How do we see?
Light hits the cornea in the front of our eye, gets refracted to form an image on the retina at the back of the eye, where it is absorbed. The retina is made up of several layers of cells. The retinal cells that directly detect light are photoreceptors, which can be classified into rods and cones. Rods and cones send signals to other neurons in the retina, particularly via the bipolar cells to retinal ganglion cells. Projections of ganglion cells collectively form the optic nerve, through which visual information travels from the retina to the brain.
Most of the information in the optic nerve is sent to the lateral geniculate nucleus (LGN) in the thalamus, which subsequently sends information to the visual cortex. The retina, LGN, and cortex all apply various forms of processing to visual information, such as changing simple light detection to the detection of spatial contrasts or particular edge orientations. While the activity of neurons represents increasingly more complex characteristics, retinotopy is preserved in LGN and early visual cortex. Retinotopy is the organization of neurons such that neighboring regions of tissue represent neighboring regions in the visual field. Retinotopy is no longer maintained in higher cortical areas, as neural representations become less related to the visual field and represent more abstract information.
Ultra Low Vision
Destruction of neurons in the visual system can cause blindness beyond the abilities of current medicine to treat. Photoreceptor death or damage to LGN or visual cortex can create deficits in corresponding parts of the visual field. Extensive degeneration can leave a person barely able to perceive light, and even then, perhaps only in small parts of the visual field. Profound visual impairment in individuals with very limited functional vision is considered ultra-low vision. Ultra-low vision can manifest itself during the natural progression of a disease, or might describe the vision bestowed upon the recipient of a visual prosthesis or a sensory substitution device. For example, the retina or another part of the visual system can be electrically stimulated to generate artificial impressions of light. While such stimulation might offer some light, movement, or crude shape perception, the amount of visual information that can be communicated to the brain with current visual prostheses is very limited, and the stimulation can therefore offer only the most rudimentary function in visual tasks.
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