1- What Is A Retinal Prosthesis?
A retinal prosthesis is a biomedical implant intended to partially restore useful vision to people who have lost their sight due to retinitis pigmentosa (RP) which severely damages the photoreceptors in the eye.
2- What Is The Argus® II Retinal Prosthesis System?
The Argus II Retinal Prosthesis System ("Argus II") is intended to provide electrical stimulation of the retina to induce visual perception in blind individuals with severe to profound retinitis pigmentosa.
In a healthy eye, the photoreceptors (rods and cones) in the retina convert light into tiny electrochemical impulses that are sent through the optic nerve and into the brain, where they are decoded into images. If the photoreceptors no longer function correctly—due to conditions such as retinitis pigmentosa (RP)—the first step in this process is disrupted, and the visual system cannot transform light into images.
Argus II is designed to bypass the damaged photoreceptors altogether. A miniature video camera housed in the patient’s glasses captures a scene. The video is sent to a small patient-worn computer (i.e., the video processing unit – VPU) where it is processed and transformed into instructions that are sent back to the glasses via a cable. These instructions are transmitted wirelessly to an antenna in the implant. The signals are then sent to the electrode array, which emits small pulses of electricity. These pulses bypass the damaged photoreceptors and stimulate the retina’s remaining cells, which transmit the visual information along the optic nerve to the brain creating the perception of patterns of light. Patients learn to interpret these as visual patterns.
3- Who Might Benefit?
Argus II is currently approved and intended for use in patients with severe to profound retinitis pigmentosa (RP) who meet the following criteria:
- Adults, age 25 years or older
- Bare light or no light perception in both eyes. (If the patient has no residual light perception, then evidence of intact inner layer retina function must be confirmed.)
- Previous history of useful form vision.
- Aphakic or pseudophakic. (If the patient is phakic prior to implant, the natural lens will be removed during the implant procedure.)
- Patients who are willing and able to receive the recommended post-implant clinical follow-up, device fitting, and visual rehabilitation.
The Argus II is intended to be implanted in a single eye, typically the worse-seeing eye.
4- What Do You See With Argus II?
The Argus II System provides a form of vision that differs from the vision you used to have. It does not restore normal vision. It does not slow or reverse the progression of your disease. In addition, it will not replace your normal visual aids. You will have to learn how to use the Argus II System with your other aides (such as a dog or a cane) and techniques. When you are not using the Argus II System, your vision will return to its original impaired state.
5- How Much Field of View Can the Argus II System Give Me?
The Argus II System delivers electrical signals to your retina that will allow you to see spots of light. The implant is designed to give you a visual field of about 3.5 inches by 6.5 inches (9 by 16.5 centimeters) at arm's length, or slightly larger than a standard 3 x 5-inch index card. However, the actual size of light you see when the system turns on all the electrodes together may be larger or smaller.
6- What Are the Probable Benefits of the Argus II System?
The Argus II System may help you do tasks visually, rather than by touch. During the clinical trial, some subjects were able to locate lights and windows, follow lines in a crosswalk, or avoid running into things as they walked. Some subjects could sort laundry or determine where other people were located in a room. About half of the subjects were able to read very large letters (about 9 inches high viewed from 1 foot away or about 23 centimeters high viewed from 0.3 meters away). A few subjects were able to read smaller letters (about 1-2 inches high viewed from 1 foot away or about 2.5-5 centimeters high viewed from 0.3 meters away) and short words. In addition, many subjects reported enjoying seeing light and motion after being blind for many years and having a greater feeling of connection to their environment and to other people.
Results varied among clinical trial subjects. While the majority of subjects received a benefit from the Argus II System on multiple tests and exams, some subjects reported receiving no benefit.
7- Is A Surgical Procedure Required?
Yes, a surgical procedure is used to implant Argus II. The surgery can typically be completed within 4 hours and requires general anaesthesia. A one-night hospital stay may be required. Pre- and post-operative medication will be defined as necessary by the physician. Support from family or friends is recommended (but not required) for the post-operative follow-up.