This treatment method, which is currently at the research stage, is suitable for blind people whose optical nerves and associated regions of the brain are still intact, as is the case, for instance, with the inherited retinal disease RP.
In the newly-developed retinal chip, tiny light-sensitive photodiodes take over the function of the photoreceptor cells (rods and cones) which have perished by converting light into electronic signals and steering these signals to the nerve cells in the retina. The implanted retinal chip takes over the function of the photoreceptor cells which have perished. Subsequently, the retina performs ‘translation’ work which is important for the recognition of images. The electrical impulses are relayed via the optical nerve fibres to the visual cortex in the brain, thus enabling perception of vision there.
During the development of the chip, the research team was faced with a variety of problems which have been successfully solved in the last few years, amongst others: whether or not a foreign body can be placed permanently under the retina in the vicinity of the location of sharpest vision, how durable the chip materials are in the eye fluids, and whether or not the strength of the signals from the tiny photodiodes is sufficient to drive the chain of information into the brain. The trigger levels for the stimulation of optical nerve cells also had to be researched.
The goal of the project is, by implanting the chip, to restore a certain level of vision which is useful for daily life and allows at least some orientation, e.g. the localisation of objects. In numerous experiments (partly on animals), trigger levels for the electrical stimulation of optical nerves and the limit values for safe use were first determined. The pilot study was intended to test the safety and tolerability, as well as the functional results, within the framework of an implantation which was limited to four weeks. It served to gain knowledge with respect to numerous technical and medical data which are indispensable for further optimisation of the retinal chip.
Seven patients successfully underwent operations which healed well. All of the patients tolerated the implant, which was operatively placed under the retina by PD Helmut Sachs, M.D., or Professor Karl-Ulrich Bartz-Schmidt, well. There were no detachments of the retina, inflammations, rejection reactions, severe bleeding or the like. The power supply cable laid by PD Dorothea Besch, M.D., and PD Florian Gekeler, M.D., under the facial skin and the scalp also caused no problems. Swellings of the retina were able to be treated well; slight bleeding was quickly resorbed. The new operational method, executed through the choroid coat of the eye, can be considered to be safe.
The electrical stimulation brought much important and valuable knowledge about the behavioural response of the retina and thus about the optimal electronic setting of the chip. Several technical improvements could already be made during the course of the study. Due to the electrical stimulation, patients could perceive light in certain shapes and patterns. Visual perceptions via the chip itself made the recognition and localisation of sources of light (windows, lamps) possible, which is of great importance to selfsufficient orientation. The patients sometimes noticed light objects (e.g. crockery) against a dark background.
The pilot study (leader: Professor Zrenner, MD, co-ordination: Barbara Wilhelm, PhD) provided extremely valuable data on the strength of the stimulation currents and their optimum duration and polarity, on the temporal sequence of light stimulants, on spatial resolution, on the homogeneity and stability of the perceptions and on the tolerability and reactivity of the retina.
All patients viewed their participation in the study as a positive, exciting experience, despite the stress of the operation and the often protracted tests. At the end of the study they declared that, if they had to choose again, they would again decide to participate.
Patients who are blind in at least one eye, or who can only localise light so indistinctly that it is insignificant with regard to their orientation, can take part in the study. The participants must be at least 18 years old and no older than 75 years old, and must be suffering from retinitis pigmentosa, chloroideremia or extensive cone-rod dystrophy. They must have had at least twelve years experience of vision in their lives and thereby have had at least 5 percent sharpness of vision. A retinal implant as a potential vision implant is out of the question for a wide variety of causes of blindness, e.g. glaucoma (cataract), diseased optical nerve, disorders of the blood supply to the retina, detachment of the retina or blindness due to accidental injuries.
Patients with age-related macular degeneration can also not participate in the study at present.
For information regarding patient recruiting, please write to the Retinal Implant Info-Center in Tübingen or call the Retina Implant AG +49 (0) 7121 364030
Retina Implant Info-Center
Telefon: +49 (0) 7071 298-7316
Fax: +49 (0) 7071 2950-21