Retinal implants

Information about the clinical trial

On 15 April 2008, as part of an international Phase I clinical study, surgeons at Moorfields carried out two successful operations to implant an artificial electronic retinal device into the eyes of two blind patients. This was the first time that such devices have been implanted in Britain.

The Moorfields research team lead by Mr Lyndon da Cruz, who is a Consultant Retinal Surgeon, included Mr Andrew Webster, Consultant Ophthalmologist and specialist in inherited diseases, and Professor Gary Rubin whose interest is in visual rehabilitation.

Below is some more information about the trial.

What is the condition?

The trial involves patients with very severe Retinitis Pigmentosa which is an inherited degeneration of the retina. It is a group of conditions that have in common abnormality of retinal receptors (rods and cones) that result in severe vision impairment in and in some cases, total blindness.

The retina is made up of a layer of cells called photoreceptors which can detect light. The cells then convert the light into electrical impulses and transfer these to the brain via the optic nerve. In Retinitis Pigmentosa the layer that captures the light may be lost but the nerves that carry the signal to the brain may still be present.

Is this treatment available now?

At the moment the implant is only available as part of a clinical trial. Therefore, it is not available to patients outside of the trial. As it is a trial, the researchers will need to establish that the procedure is safe. The subjects will need to be followed up to assess the long term effect of the treatment, and the overall results may not be available for some months.

Can I take part in the clinical trial?

All of the people involved in the trial need to be screened to confirm that they have retinitis pigmentosa and that the condition is severe enough to enter the trial. People on the trial will be patients of Moorfields.

What do the researchers hope to achieve?

In this form of retinal degeneration the photoreceptor cells are completely lost. The aim is provide this lost function. To do so the picture is captured with a camera and this signal is transmitted to a device implanted in the eye. The device stimulates the remaining nerves by way of an electrode panel in the eye. The signal is then passed up the optic nerve to the brain.

Are there plans for future trials for other forms of retinal conditions?

It would be possible to use this device in other conditions where the photoreceptors are lost and there is good function of the optic nerve. However, this first trial is for severe Retinitis Pigmentosa only. Results from this first trial are likely to provide an important basis for many more protocols in the future.

How does the Argus II device work?

The device consists of a tiny camera and transmitter mounted in sunglasses, an implanted receiver, and an electrode-studded array that is tacked to the retina. A video processor and battery pack worn on the belt powers the entire device. The camera on the glasses captures an image and sends the information to the video processor, which converts the image to an electronic signal and sends it to the transmitter on the sunglasses. The implanted receiver wirelessly receives this data and sends the signals through a tiny cable to the electrode array, stimulating it to emit electrical pulses. The pulses induce responses in the retina that travel through the optic nerve to the brain, which perceives patterns of light and dark spots corresponding to the electrodes stimulated.

How long will it work for?

We cannot yet conclusively state what the expected lifetime of the implant is. Second Sight has undertaken extensive verification testing that indicates that the device should last many years, but the final determination on expected lifetime has yet to be made. The MHRA has provided us with approval to begin our clinical trial with the device after reviewing our extensive test data.

How big is the implant? Will it be visible from outside?

There is a portion of the implant that sits on the outside of the eye, underneath the conjunctiva (the white-pink tissue around your cornea). Because it is covered by the tissue this portion of the device is not visible, although the bump that it creates under the tissue may be visible in some subjects. There is another small part of the device that goes into the eye and gets attached to the retina with a micro-tack. None of this portion would be visible to someone looking at the subject, although a physician will certainly be able to see this part of the device inside the eye when performing a routine eye exam.

What else does the subject wear and what does it look like?

There are several external pieces that the subject has to wear. The most noticeable are the glasses which house the small camera and transmitting antenna. These glasses are dark and stylish. There is a cable that runs from these glasses to a processing unit that is about the size of a SONY Walkman®. The cable can run under clothing if desired and the processing unit can be held in the hand, attached to a belt or contained in a case or purse.

Is it easy to operate?

The implanted subjects to date have found the system relatively easy to operate. The system and implant is set up in the clinic so that the patient need only control a few aspects such as on/off, and simple image controls such as brightness. Additionally the subject is trained on how to change the rechargeable battery.

Where has the technology come from?

The technology was developed by Second Sight® Medical Products, Inc., located near Los Angeles, California with the goal of creating a retinal prosthesis to provide sight to patients blinded from outer retinal degenerations, such as Retinitis Pigmentosa. Through dedication and innovation, Second Sight’s mission is to develop, manufacture and market implantable visual prosthetics to enable blind individuals to overcome their disability and achieve greater independence. The company has received extensive U.S. federal support in developing this new technology and is grateful for the forward thinking of the National Institutes of Health/National Eye Institute and the Office of Science at the Department of Energy in supporting significant aspects of this work.

Where else are these clinical studies taking place?

This study is being performed at several sites across the United States and Europe. Please check (http://clinicaltrials.gov/ct/show/NCT00407602 ) for the most up-to-date list of participating sites.

Where can I get more information about Retinitis Pigmentosa?

For information and support for people with RP:
British Retinal Pigmentosa Society
P.O.Box 350 Buckingham MK18 1GZ

Telephone - 0845 123 2354

Fax - 01280 815900

E-mail - info@brps.org.uk

Website - http://www.brps.org.uk