A look to the future of subretinal implant
A subretinal implant has been developed that is designed to take the place of the photoreceptors in patients with retinal degenerations, such as retinitis pigmentosa.
Tübingen, Germany—The development of a subretinal implant may be a significant advancement in terms of restoring useful vision.
The wireless, microelectronic neuroprosthetic device (Alpha-IMS, Retina Implant AG) is designed to take the place of the function of photoreceptors in patients with retinal degenerations, such as retinitis pigmentosa.
The device uses light-sensitive, subretinal detector arrays and amplifiers to convert light into signals that can stimulate the bipolar cell neurons via tiny metal electrodes, investigators explained. They published their clinical results in the Proceedings of the Royal Society, Biological Sciences (2013;280:20130077).
The chip on the implant is 3 × 3 mm in size and provides a visual field of 10º × 10º. The implant can be used indoors or outdoors, as sensitivity and contrast can be adjusted by the patient.
The results reported refer to 9 blind patients (4 women, 5 men; mean age, 46.9 ± 7.2 years; range, 35 to 62 years), with the device implanted unilaterally from the University of Tübingen, Centre for Ophthalmology, Tübingen, Germany.
Before implantation of the device, 8 patients had light perception vision without correct light source localization and 1 patient was completely blind.
How it works
The implant receives power and control signals by wireless transmission via a subdermal receiver coil behind the ear. From there, a subdermal cable leads to the orbit and ends in a thin, subretinal foil with gold wires contacting the subfoveally positioned chip.
An external antenna-coil kept in place magnetically above the subdermal coil behind the ear provides power, via transdermal electric induction. It is connected by a thin cable to a small battery pack that also contains a control panel where patients can adjust the brightness and contrast of the perceived image.
The group led by Prof. Eberhart Zrenner, MD, from the Centre for Ophthalmology, reported that after implantation of the device light perception was restored in 8 of the 9 patients, light localization in 7, motion detection in 5, grating acuity measurement in 6 up to 3.3 cycles per degree, and visual acuity measurement with Landolt C rings in 2 up to a Snellen visual acuity of 20/546.
Investigators also reported that the identification, localization, and discrimination of objects improved significantly (p < 0.05 for each subtest) in 8 patients. During the 9-month follow-up period, 3 patients could read letters spontaneously and 1 could read letters after training in an alternative-force choice test. Five subjects reported implant-mediated visual perceptions in daily life within a field of 10º to 15º of visual angle.
“These data showed that subretinal implants can restore visual functions that are useful for daily life,” said Katarina Stingl, MD, the study physician in charge.
The authors commented, “Our approach using subretinal light sensitive electronic implants is the only one that has successfully mediated images in a trial with freely moving blind persons by means of a light sensor array that moves with the eye. All the other current approaches require an extraocular camera that does not link image capture to eye movements, which, therefore, does not allow the utilization of microsaccades for refreshing the perceived images. Although the restoration of vision described here is limited to black and white blurred vision, blind persons with no alternative therapy options regard this type of artificial vision as an improvement in everyday life.”
Based on the study results, they concluded that the wirelessly driven implant, positioned in the subfoveolar subretinal space can restore useful vision in daily life for at least two-thirds of the blind patients investigated.
“The long-term stability and safety and development of visual recognition abilities via learning effects over a longer observation period will be addressed in future patients who receive this implant,” the authors said.
The implant received CE mark approval in Europe. A multicenter study is under way in Oxford, Hong Kong, London, Budapest, Hungary, and other centers with another 19 patients that have already received the implant.
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