Epiretinal prosthesis outcomes remain encouraging for retinitis pigmentosa

By Cheryl Guttman Krader; Reviewed by Stanislao Rizzo, MD

Pisa, Italy-In ongoing follow-up now extending to 3 years, the Argus II Retinal Prosthesis System (Second Sight Medical Products) remains well tolerated and continues to provide patients with benefits of improved visual function and quality of life, said Stanislao Rizzo, MD.

Dr. Rizzo was the first surgeon in the world to implant the retinal prosthesis after it became commercially available. That was in October 2011, and his series now includes 12 patients blind from retinitis pigmentosa. All had no light perception vision at the time of implantation and they ranged in age from 30 to 65 years.

During follow-up of 12 to 32 months, there have been no serious complications related to the surgery or the device. Patient feedback and results from formal testing show the recipients have maintained improvements in mobility, orientation, and object identification.

In addition, Goldmann visual field testing improved in all patients, and one patient achieved grating visual acuity.

While those outcomes are amazing considering that all patients had no light perception vision prior to their surgery, even more important is the tremendous positive impact the implant has had on quality of life, said Dr. Rizzo, director, U.O. Chirurgia Oftalmica, Ospedale Cisanello, Azienda Ospedaliero Universitaria Pisana, Pisa, Italy.

“We have shown the benefits of the retinal prosthesis using validated quality-of-life instruments,” Dr. Rizzo said. “However, the spontaneous comments of patients, who for example are thrilled to be able to recognize family members for the first time in many years, tell an even more compelling story.”

“Clearly, the [retinal prosthesis] is a revolutionary advance for improving the lives of patients with a very debilitating disease, but we expect it is just the beginning as the technology improves and new systems are developed,” he said. “The Argus II is already the second generation of the epiretinal prosthesis, and there have also been numerous upgrades to its software and some of its hardware components.”

The retinal prosthesis system is comprised of a video camera mounted on a pair of glasses, an externally worn video processing unit (VPU), an inductive coil (antenna) fixed on the sclera, and a 60-electrode epiretinal array that is implanted onto the macula via a pars plana approach. The camera receives visual input that is converted to a stimulation pattern by the VPU. The VPU transmits the data and power wirelessly to the antenna that is hardwired to the epiretinal array. When the information is transferred to the array, it stimulates the viable retinal neurons below the photoreceptors (bipolar and ganglion cells). Their signal is relayed to the visual cortex via the optic nerve.

Dr. Rizzo said that the implantation surgery is not that technically difficult for skilled vitreoretinal surgeons.

However, it is long and involves some novel elements both within and outside of the posterior segment, such as for fixation of the epiretinal array to the macula and of the antenna to the sclera.

“Surgeons who perform the implantation need to be a ‘complete’ surgeon, and they need to know that relative to familiar operations, it is an arduous procedure,” he said.

“However, the surgical time is significantly reduced after passing the learning curve,” Dr. Rizzo said. “While our first procedure took 4 hours to complete, in later cases we finished the implantation in less than 2 hours.”

Dr. Rizzo said the prosthesis was safely implanted in all 12 patients. Postoperative complications included elevated IOP in one patient, which was controlled with topical medication, and a moderate detachment of the choroid in one patient, which resolved spontaneously.

“Patient safety is always paramount, and so it is important to note that the device appears to be highly biocompatible and there have been no real concerns for implanted patients,” Dr. Rizzo said.

Choosing candidates

Dr. Rizzo said that careful patient selection is critical when choosing recipients for the prosthesis, and there are a variety of issues to consider. Eligible patients are those with severe outer retinal degeneration, but with surviving inner retinal cells and ganglion cells able to respond to the electrical stimulation. As another anatomic requirement, axial length must be between 22.5 and 27 mm because the cable running from the array to the antenna is a fixed length.

Patients also have to be in good general health because the lengthy procedure is done under general anesthesia. In addition, they need to have appropriate expectations for outcomes, and they and their families must be judged as being motivated to reliably comply with the intense rehabilitation process.

“Patients need to understand and accept that the prosthesis provides a limited form of vision, and this is discussed at length and several times in the preoperative consultations,” Dr. Rizzo said.

“After the surgery, patients need to learn a new form of vision that is completely different from natural vision. The outcome of the procedure depends not only on the success of surgery, but also on the patient’s participation in the rehabilitation training program.”

Stanislao Rizzo, MD

E: stanislao.rozzo@gmail.com

This article was adapted from Dr. Rizzo’s presentation during Retina Subspecialty Day at the 2014 meeting of the American Academy of Ophthalmology. Dr. Rizzo has no relevant financial interests to disclose.