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One-year outcomes with a subretinal implant for patients blinded by retinitis pigmentosa demonstrated a marked improvement in visual capabilities.
Take-home message: One-year outcomes with a subretinal implant for patients blinded by retinitis pigmentosa demonstrated a marked improvement in visual capabilities.
By Cheryl Guttman Krader; Reviewed by Helmut Sachs, MD
Dresden, Germany-Early experience with a subretinal electronic chip (Alpha IMS, Retina Implant AG) shows it is safe and can restore useful vision to a majority of patients who are blind because of retinitis pigmentosa, said Helmut Sachs, MD.
The device received the CE mark for commercial use in Europe in July 2013, and a study to gain FDA approval in the United States is planned.
“Electronic implants are presently the only strategy that allows patients blind from hereditary retinal disease to regain some vision,” said Dr. Sachs, senior consultant and chairman, Department of Ophthalmology, Clinic Dresden-Friedrichstadt, Germany. “As one approach, the subretinal implant offers some advantages, and it has been associated with encouraging outcomes.
“Now, we look forward to assessing its stability and performance long term and to technical advances that will improve visual resolution and contrast vision to further increase the implant’s value to patients in daily life,” said Dr. Sachs, who is also an investigator in an ongoing multicenter study evaluating the subretinal implant.
The subretinal chip is a 3- × 3-mm square containing 1,500 electrodes. It is implanted transchoroidally beneath the fovea and without any need for fixation.
“The subretinal chip replaces degenerated photoreceptors with microphotodiode arrays,” Dr. Sachs said. “Vision is restored by stimulating the ganglion cells because the inner retina is still intact in patients with retinitis pigmentosa even years after blindness occurs.”
The subretinal chip receives power inductively from a transmitter coil that is placed subdermally behind the ear. Originally the chip and transmitter coil were linked via a cable, but now the system features wireless power and signal transmission.
Dr. Sachs highlighted that unlike the commercially available epiretinal implant (Argus II, Second Sight), the subretinal device requires no external camera for image capture. Rather, with the subretinal implant eye movement helps localize objects and refreshes the perceived image, taking advantage of the efferential copy in the brain and avoiding any fading.
Compared with the epiretinal implant, the subretinal chip also has 25 times more electrodes and fewer components.
“Because it has more electrodes, the subretinal implant may allow light and dark images to appear more vibrant, thereby enhancing visual resolution,” Dr. Sachs said.
Implantation of the subretinal chip is performed after vitrectomy. First, a portion of the retina is detached in the far periphery. The so-created bleb is stabilized with a viscoelastic solution.
Next, the sclera is prepared down to the choroid in the corresponding area to the bleb. The choroid is then opened without any bleeding. The implant is advanced under the foveal region with the help of a guide, and the fixation is done outside of the eye.
To date, 29 patients have been enrolled in a multicenter study. Dr. Sachs reviewed outcomes for 26 patients followed to 1 year after surgery. The mean length of time since the patients were last able to read was 17 years.
Visual function is being evaluated using monitor-based tests for light perception, localization, movement detection, grating acuity, and visual acuity with Landolt C-rings. The tests are performed with the implant power source on and off, in randomized order and with the patient masked to the condition.
In addition, patients are being evaluated for their ability to detect, localize, and identify objects, read letters, and for their visual experiences in daily life.
Four (15%) patients failed to gain light perception after implantation, due either to a technical issue or some anatomic problems. Considering all 26 patients, the monitor-based testing showed 15 (58%) patients were able to localize a light source, 14 (54%) achieved measurable grating acuity of up to 3.3 cycles/degree, 6 (23%) had motion perception of up to 35 cycles/degree, and 4 (18%) had measurable visual acuity (up to 20/546) with the ability to read letters 4 to 8 cm.
“Interestingly, when we monitored eye movements in these patients, we could see that when the implant was on, the movements strongly reflected the percepts of a stimulus such that when they noticed a percept, eye movement ceased,” Dr. Sachs said.
Subjectively, 12 (46%) patients reported useful visual experience in terms of perceiving details of objects and 7 (27%) were able to localize objects in daily life without details.
The implantation procedure was safe. The only adverse events encountered were development of elevated IOP and shallow subretinal bleeding postoperatively in 1 patient. The event was managed surgically by r-tPA injection, and the affected patient has the best visual acuity in the series, Dr. Sachs said.
Helmut Sachs, MD
This article was adapted from Dr. Sachs’ presentation during the 2014 meeting of the American Academy of Ophthalmology. Dr. Sachs is a shareholder of and a paid consultant to Retina Implant AG.