According to a recent WHO estimate more than 37 million people suffer from blindness worldwide. While cataract and trachoma are the main causes of blindness in developing countries, age-related macular degeneration (AMD) and hereditary retinal dystrophy (HRD) significantly contribute to the respective number in developed countries. (HRD is the collective term for a large, heterogeneous group of genetically determined diseases that lead to a progressive loss of photoreceptors.)
In both AMD and HRD, however, it has been found that the inner retina remains intact for a long time, and for this reason retinal implants have been proposed as a means of treating blindness in patients suffering from AMD and HRD. Recent studies with electronic retinal implants have clearly demonstrated their feasibility in principle.
What is a retinal implant?
The intraocular part of the subretinal implant is a silicon-based active microchip with 1500 individual units serving as pixels. Each pixel consists of a photodiode which can sense local light intensity along with amplifying circuitry which is connected to a local stimulation electrode made of iridium (Ir). The stimulus current provided by the electrode is dependent on the brightness at each photodiode. The carrier substrate for this chip is a piece of polyamide film which also carries leads for connecting the chip to a separate power supply.
Who eligible to enter the study?
Patient with typical signs of end-stage retinitis pigmentosa (RP), rod-cone dystrophy and choroideremia can participate in the study. Participants should have a visual acuity of less than hand movement detection, and not being able to localize the light source. The inclusion criteria for the study are retinitis pigmentosa and HRD without any residual vision. The inclusion criteria for successful implantation are acceptable general health and an absence of severe cardiovascular disease. Patients suffering from other eye diseases or with sufficient residual visual function for crude orientation or navigation (e.g. localization of light) are excluded.
Primary and Secondary Outcome Measures