Assessing visual cortex in candidates for retinal prosthetics

Plain English summary of protocol

Background and study aims
Macular degeneration (MD) is the most common cause of vision loss in the western world. It mostly effects the elderly (age-related macular degeneration, or AMD). It involves the gradual damage to a part of the eye called the macula. The macula is a tiny area at the centre of the retina (the layer at the back of the eye which is sensitive to light), which is responsible for central vision (seeing what is directly ahead). Over time, the damage to the macula can lead to central vision becoming distorted or blurry, eventually causing a blank patch in the centre of a person’s vision. In most cases, AMD is caused by fatty-protein deposits called drusen collecting under the retina (dry AMD) over a long period of time; currently there is no cure or effective treatment for this type. About 10% of people suffering from AMD have what is known as wet AMD (or neovascular AMD). In wet AMD, the macula becomes damaged and new blood vessels start to grow behind the retina. These blood vessels are generally very weak and prone to leakage, causing the macula to swell and vision to deteriorate very quickly. This form can be treated to improve vision and to prevent further damage. MD is particularly devastating because it is central vision that is most critical for daily activities such as reading, driving, recognising faces, watching television, etc. New therapies are being developed to treat and restore vision in patients with dry MD and other eye diseases. One approach is to implant an electronic chip in the eye to replace the function of the cells damaged by the disease. The Argus® II Retinal Prosthesis System, developed by Second Sight Medical Products, Inc., is the most successful example of this technology to date. NHS ethical approval has recently been granted to test the Argus® II implant in patients with MD in a small study run by Professor Paulo Stanga at the Manchester Royal Eye Hospital. A large proportion of the parts of the brain involved in vision (the 'visual cortex') receive information from the central retina of the eye. MD therefore effectively cuts off these brain areas from visual input. When patients have been partially or fully blind for many years, these 'unused' parts of the brain may begin to take on new roles and process other information, or they may even degenerate and lose their ability to function altogether. Most research on vision restoration has focused on treating the eye. However, since visual perception ultimately takes place in the brain, the visual cortex must be able cope with inputs from the eye once they are restored. With participants from the study in Manchester, magnetic resonance imaging (MRI) will be used to assess the structure and function of the visual cortex of the brain in MD patients before and after implantation with the Argus® II Retinal Prosthesis System. It will lay the groundwork for a larger study aimed at answering the following questions, which have both clinical and scientific significance:
1. Which measures of brain structure and function prior to retinal prosthetic implantation best predict successful restoration of vision in patients with macular degeneration?
2. Do neural changes occur in brain structure and function when visual inputs are reintroduced?
3. Which measures of brain structure and function after implantation best predict the success of retinal prosthetic implants in restoring sight?
It is hoped that answering these questions will contribute to the development of tools to help clinicians predict the success of retinal prosthetics and other treatments aimed at restoring peoples sight. In addition, researchers hope to gain a better understanding of brain plasticity (changes to the brain) and the mechanisms underlying recovery of sight in adults with MD.

Who can participate?
Participants from the Argus II Retinal Prosthesis System Dry AMD Feasibility Study in Manchester (https://clinicaltrials.gov/show/NCT02227498).

What does the study involve?
All participants undergo MRI scanning to look at and compare two regions of the brain. The first is the “lesion projection zone” of the brain, which is the part of the brain that normally receives input from the damaged part of the eye. The second is the “intact projection zone”, which is the part of the brain that receives input from the undamaged parts of the eye. The researchers also use MRI to look at the effects of the surgical implantation with the retinal prosthesis. The participants undergo two sessions, once before their retinal implantation and once 12 months after it has taken place.

What are the possible benefits and risks of participating?
There is no guarantee of any direct benefit to participants in this study. Potential harmful risks will be avoided by screening participants to ensure that MRI will not harm them. In addition, all MRI scanning procedures will follow the implant manufacturer’s guidelines. Some people might feel claustrophobic or discomfort in confined spaces such as the MRI scanner. If so, these participants will not be included in the study. Some participants (particularly those who have not had an MRI scan before) may find it uncomfortable to remain as still as possible for an extended period of time. Foam cushions are used to minimise any discomfort and help support the head in a static position. As the MRI scanner operates at high noise levels, all participants are given ear plugs and plenty of cushioned head support to maintain noise levels within safe limits. A two-way intercom is used by the MRI operator to communicate with the participant at regular, frequent intervals (every few minutes). Participants will also be given an emergency squeeze ball to indicate if they feel at uncomfortable at any time either during a scan or between scans. This will stop the scanner immediately and the MRI operator will enter the scanning chamber to retrieve the participant.

Where is the study run from?
University of York (UK)

When is the study starting and how long is it expected to run for?
February 2015 to February 2016

Who is funding the study?
Centre for Chronic Diseases and Disorders (UK)

Who is the main contact?
Dr Heidi Baseler
heidi.baseler@york.ac.uk

Contact information

Dr Heidi Baseler
Scientific

University of York
Department of Psychology
Heslington
York
YO10 5DD
United Kingdom

ORCID ID	0000-0003-0995-8453
Phone	+44 (0)1904 322862
Email	heidi.baseler@york.ac.uk

Study information

Eligibility

Locations

Countries of recruitment

• England
• United Kingdom

Study participating centre

Sponsor information

University of York
University/education

Research Innovation Office
Innovation Centre
York Science Park
York
YO20 5DD
England
United Kingdom

Phone	sue.final@york.ac.uk
Email	sue.final@york.ac.uk
"ROR"	https://ror.org/04m01e293

Funders

Funder type

University/education

Results and Publications

Editorial Notes

16/03/2018: No publications found, verifying study status with principal investigator.