NEW ORLEANS — For patients with advanced retinitis pigmentosa, the ability to perceive images and movement can be improved with the implantation of a retinal prosthesis, new research has shown.
The Argus II Retinal Prosthesis System was designed by Second Sight for patients with severe to profound outer retinal degeneration, whose remaining visual acuity is worse than 2.3 logMAR in both eyes. Such patients have bare light perception or no light perception in both eyes, evidence of intact inner layer retina function, and previous ability to see forms.
Interest is high in retinal prostheses that can help people with outer retinal dystrophies identify common objects, said Abdhish Bhavsar, MD, from Retina Center Minnesota in Minneapolis.
The studies presented here at the American Academy of Ophthalmology 2013 Annual Meeting involve a small number of patients but deserve attention, he told Medscape Medical News.
"They will get this attention because this is the first artificial retina and it's the furthest along in development," he said. "While the device is rudimentary, it can bring vision to the patient with no outer vision, and it's outstanding that it can do that."
Two investigators presented safety and efficacy data from patients who have undergone implantation.
Mark Humayun, MD, the Cornelius Pings Professor of Biomedical Sciences and director of the University of Southern California Eye Institute in Los Angeles, presented a postapproval update on 70 patients implanted with the device, including 20 in the United States.
The device "can reliably withstand long-term implant — more than 5 years — in a significant number of subjects, based on more than 140 cumulative subject-years," Dr. Humayun reported. It "can improve patients' orientation and mobility, activities of daily living, and well-being."
The device consists of an implanted retinal prosthesis, a miniature video camera that is housed in a patient's eyeglasses, and a processing unit worn by the patient. The image captured by the camera is processed into instructions that are transmitted wirelessly to the implant, which is fitted with 60 electrodes that can be individually programmed. These electrodes pulse to stimulate cells in the retina, transmitting visual information along the optic nerve to the brain and creating the perception of patterns of life.
Results from a study of 8 patients were presented by lead investigator Yvonne Luo, MA, from Moorfields Eye Hospital NHS Foundation Trust in London, United Kingdom.
The 8 patients were asked to identify white or metallic objects (such as a teapot, cup, and plate) against a dark background. The outlines of the same objects were then enhanced when black cardboard cut-outs were placed over parts of the objects.
"When subjects see the full solid object, there is so much brightness that the definition is marred. Also, the object appears only for a few seconds, then starts to fade. So we thought that if they could find the outline of the object they might see it better," Luo explained.
The tests were conducted with the device turned on in standard mode, with it turned on in scrambled mode as a positive control, and with it turned off as a negative control.
More patients were able to identify solid objects with the device switched on than with it in scrambled mode or with it switched off (32.8% vs 26.2% vs 12.5%; P = .02). The pattern was the same when the objects were outlined (41.4% vs 20.7% vs 9.4%; P = .005).
"Despite the small sample size, the results achieved statistical significance because of the magnitude of change in the performance of the device in each subject," Luo reported.
"This test actually has a practical application in terms of modifying the patient's environment," she explained. "We can design objects for the patient's home that can be outlined. For example, if the person keeps bumping into the edge of the sofa, we can outline the sofa. We hope to be able to translate more of what patients can do in the artificial setting into the home. It also allows for future developments in image capturing and processing. We hope to improve the software so that we can add outlines to the images seen by the patient."
The fact that the appearance of objects is so different from the patients' experience with natural vision has led to a reality check for many, she said. "The initial excitement is huge, but it wears off to some degree because patients expect to see what they used to see, and this is quite different," she noted.
"You have to realize that these individuals have artificial vision with the device. The way a teapot looks with the device is not the same as the subject remembers. Artificial vision is so different that patients have to essentially relearn what objects look like," Luo told Medscape Medical News.
Dr. Humayun presented a postapproval update, as of August, describing the function and safety of the system in 31 patients from 10 surgical centers in France, Germany, Italy, the Netherlands, Saudi Arabia, and the United Kingdom
All 31 patients had end-stage retinitis pigmentosa and had used the device for an average 10 months. The mean age of the patients was 53 years.
There were 2 serious adverse events in the cohort: 1 case of hypotony and 1 case of conjunctival dehiscence. There were 16 nonserious adverse events in 9 patients. All adverse events occurred within 2 months of implantation.
"In these 31 patients who have had the device for up to 22 months, there have been no failures and no need for explantation," he said.
In the clinical trial of 30 patients that led to FDA approval of the device, 23 serious adverse events were observed in 11 patients, including hypotony, erosion and dehiscence of the conjunctiva, retinal detachment, and inflammation.
There were fewer patients with acuity below 2.9 logMAR at 5 years than at 1 year (30% vs 50%). In the clinical trial, the best visual acuity attained was 20/1260 (1.8 logMAR). The ability to successfully navigate to the door improved from about 25% at baseline to 60% at 2 years; this was sustained at 5 years, Dr. Humayun reported.
The surgical implantation procedure has become more refined, and can now be performed in less than 2 hours, he said.
Dr. Humayun said he has "enjoyed talking to patients about some of the things they can do in daily life."
"They can locate doors and windows, sort light and dark clothes, stay within a crosswalk, avoid obstacles, track players on a field, feel more socially connected, enjoy being visual again, and do fun things, such as watch fireworks," he said. "The device allows patients to be more involved with their families."
The first round of clinical centers for implantation in the United States has been established, which means that more patients will have access to the device.
Future software improvements are underway, including a digital zoom that will achieve a 20/200 level of vision. Other treatments in development for retinitis pigmentosa include an implanted microchip, electrical stimulation therapy, implantable capsules of timed-release medication, nutrient therapies to reduce retinal damage, and gene therapies to halt or reverse the disease.
Dr. Humayun reports a financial relationship with Second Sight Medical Products. Dr. Bhavsar has disclosed no relevant financial relationships.
American Academy of Ophthalmology (AAO) 2013 Annual Meeting: Abstract PO181. Presented November 15 and 17, 2013.
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Cite this: Caroline Helwick. Prosthesis Improves Vision in Retinitis Pigmentosa - Medscape - Nov 18, 2013.