Craig Blackwell, MD
Ophthalmology

Santa Cruz, CA
Diplomate: American Board of Ophthalmology
Fellow: American Academy of Ophthalmology

Welcome to the Website of Craig Blackwell, MD

An Ophthalmology Practice in Santa Cruz, CA

Artificial Retina Update 2011

Creating an artificial retina to restore lost vision has been a dream for a long time, but it has seemed so far out of reach.

Treatments to repair or replace other damaged parts of the eye, like cataract surgery and corneal transplant, have met their technical challenges to become very successful, but repairing a damaged retina has been a special challenge.

In this section we will summarize progress made toward the creation of an artificial retina as of mid 2011.

A longer version with more details is available on YouTube. To go there click on the link below.

YouTube Video: Artificial Retina Update 2011.

The Retina

Let us start with a little review.

In the front of the Eye, the Cornea, Iris and Lens focus incoming light rays to form a sharp image on the Retina.  The Retina is a layer of nerve tissue that lines the inside of the eye. It functions like film in a camera. You can think of it as an extension of the Brain.

If it is damaged it is not a simple task to replace it or even connect to what remains. Certain retinal diseases like Retinitis Pigmentosa, and more commonly,  Macular Degeneration, result in loss of retinal photo-receptors, but the rest of the retinal nerve structure is still intact. So the strategy is to replace the function of the photo-receptors with a video camera and somehow connect to and send information through the remaining intact nerve cells.

Retinal Layers

These are all the layers of the Retina.

It is a little disorienting at first. Light comes in from the top and must filter through the top and middle layers of nerve cells to reach the photo-receptors in the bottom layer. The Rods and Cones are the cells that sense light and generate nerve impulses …which go through several intermediate cells that eventually carry the nerve impulses to the Brain. In the brain the Morse code of nerve impulses is assembled into an image.

The bottom layer of the Retina, the Pigment Epithelium, is also important. It consists of pigment cells that support the function and metabolism of the Retina.

Rods and Cones

There are a variety of diseases that affect the Retina causing loss of vision.

In some diseases vision is lost because the Photo-receptors, the Rods and Cones are damaged.

Retinitis Pigmentosa

The paradigm for this kind of retinal disease is Retinitis Pigmentosa, or RP.  It is an inherited disease in which the photoreceptor cells gradually die. In this picture of RP, the two things you notice are the characteristic pigment clumping around the edge of the picture, and the pale area around the center. Peripheral vision is lost first, but eventually, central vision is lost also. Macular Degeneration is another example of retinal disease affecting photoreceptors, which is much more common.

In these diseases, photoreceptors are lost, but the other nerve cells, the bipolar and ganglion cells, are still intact. This is a critical point, because the remaining cells give a point of connection to the nervous system.  Note that this is different from diseases like glaucoma, where it is the ganglion cells that are damaged. Unfortunately, that means there are no remaining intact neurons in the eye to connect to.

So the challenge in restoring vision in diseases like RP and MD is to build a device that senses an image and somehow connects to the remaining intact nerve cells, stimulating them in a manner that mimics natural retinal function.

Artificial Retina Design Concept

Here is one design for such a device, that you may call an artificial retina. This illustration is to show the concept, we will look at details later on.

First, there is a video camera to record an image. A small camera can be attached to a regular glasses frame. The camera image is sent to a processor unit. Processing creates a simplified image matching the number of points that can be projected onto the retina. The processed image is sent by a wireless connection to the part of the device that is attached to the eye.

Within the eye there is an array of electrodes that are in contact with the retina. A small electric current at each electrode stimulates a nerve cell in the retina, similar to the nerve impulse generated by a photoreceptor. That nerve impulse is transmitted along the optic nerve back to the brain,  just as if it had originated in the retina. In this illustration the array has 16 electrodes, which is the number in the first series of actual retinal implants.

The theory sounds straightforward enough; take a camera image, turn it into an array of electric impulses, that can stimulate the surviving part of the retina, to create a useful image. Let us look at the main parts of the process in more detail, starting with the image, and then how the device works.

Real Images are Complex

The image that the camera takes contains a lot more information than the simple array can project.

We will use a 16 electrode array to illustrate the concept.

Creating a Simple Image: Processing

1. Step one is to take the camera image and simplify it, making it just black and white.

2. Step two is to reduce that image to match the number of electrodes in contact with the retina. That is the number of spots available to make an image. Here the image space is divided into 16 squares. If an image square is more that half white then the array spot is on. If it is less than half white, then the array spot is off. That makes a very simple image grid.

3. When an electrode in the array is on, the user perceives a white dot. Picture a dark background with spots of light, like a constellation in the night sky. Technically there are additional processing steps to improve the image that we will not discuss here. We will talk more about people’s actual experience with their implants after we cover a few more details about the device.

Communicating to the Eye

We have looked at how an image is created, which is done outside the eye. So, now let’s talk about how information gets from the camera and processor to the electrodes inside the eye. You could have a wire going through skin, the eye socket and the wall of the eye to the internal works, but that has increased risk of infection and may limit ocular movement.

A better answer is wire-less communication. Radio signals are generated by a coil outside the eye, and received by an antenna attached to the wall of the eye. There is still a wire that penetrates the eye wall to reach the array on the inside.  But, the opening is small, 5 mm, and its presence seems to be well tolerated.

And how do you power the electronics of the device? It turns out the answer is also radio communication. By a bit of electronics magic, one coil can be made to perform two functions at the same time. One function is sending picture information, like a radio, the other sends power, like a transformer. Eventually, it is hoped the camera and all the electronics would be contained within the eye itself.

The Argus Device

From our discussion so far, you can see the system has two parts. The Camera, Processor and sending Antenna are all external or extra-ocular. The Receiver, Electronics and Electrode Array, we will call the ocular part.

So now let’s look at actual devices that are currently being implanted.  The example we will use is the Argus series of implants, developed by a group of laboratories led by researchers at the USC. This gentleman is shown wearing a pair of glasses that has a camera and communications device mounted on the frame.  He is holding out the video processing unit.

Camera, Processor and Antenna are External

Here is a photo of the external part of the system. Attached to this glasses frame is a small camera. Trailing from it is a wire that goes to a video processing unit, which is not shown in this picture. The large black disc is the radio communication and power antenna.

Ocular Part of the Device

Here is the part of the Argus 2 that attaches to the eye. It includes the electrode array, the part that contacts the retina. That is where the magic happens.

The gold colored oval is the wire coil, for receiving information and power.  The black dome houses the electronics package. The whole thing is held in place by a supporting band that goes around the equator of the eye.  It is similar to something called a scleral buckle, which retina specialists sometimes use to repair a retinal detachment. The device was intentionally made similar to hardware retinal surgeons are already familiar with, which is a big advantage in its eventual application.

Electrode Array Inside the Eye

Here is the Argus 1, with a 16 electrode array. It is shown implanted in the eye, on the surface of the Retina. The photo has caught the light is shining off the electrodes. Note the position is in the center of the macula. It is held in place by a single tack, carefully driven into the retina.

The first implant surgeries were done in 2002. Volunteers had essentially total loss of vision, typically from RP.

Argus 1: Patient Experience

This is one of the early patients, Linda Moorfoot, who has shared her experience with the public.  She had been blind for about 10 years when she had the surgery.  When the device was first turned on she could see the spots of light.  But it took time to learn how to interpret the patterns the dots made.

After 2 years with the implant she described being able to move more confidently around her house.  At church she knows where the priest and choir are.  When someone approaches, she can turn and face them before they begin to speak.  Attending her grandchildren’s sporting events is more rewarding.

That is pretty good success with a basic 16 electrode array; from no vision to the ability to perform simple tasks.

Argus 2

The next step was the 60 electrode array, the Argus 2.

Argus 2: Patient Experience

Here is the experience of Kathy, who was blind also from RP, for 15 years before her surgery.

She also notes it takes time to learn how to interpret the spots the device presents.

Now, she is able to identify a doorway from a distance of 20 ft and walk toward it.

She is able to walk following along a white line.

At a computer screen she is able to tell the direction of a moving white line.

Man Reading

This last example shows a man able to make out large print.

Ongoing Trials Worldwide

There are 12 clinical centers in 5 countries where the Argus 2 is being implanted. There were 14 patients in the US, and 16 worldwide, that had received the Argus 2.

As of May 2011, Second Sight, the commercial company working on this announced their results to date.  Patients showed improvement in activities of daily living. Two of the patients in France have been able to start reading.

In February of 2011 the Argus 2 received the CE marking for Europe. Application has been made to the FDA for approval in the US.

A longer version with more details is available on YouTube. To go there click on the link below.

YouTube: Artificial Retina Update 2011.