The purpose of this study is to determine the long-term effects of transcorneal electrostimulation (TcES) in patients with retinitis pigmentosa (RP). In a prior study (NCT00804102) the results of short-term stimulation showed a positive effect on the visual field and other parameters. In this study, the patients will be stimulated with either 0%, 150% or 200% of the individually determined phosphene threshold.

The study was performed at the Centre for Ophthalmology, University of Tübingen, Germany. The protocol was approved by the local ethics committee. All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008. Informed consent was obtained from all patients for being included in the study. The study was conducted according to the standards of GCP, the European Union Directive for Medical Devices, and the German Medical Product Law.

Patients were seen at 14 visits over a period of 78 weeks: one baseline visit (screening), followed by 12 visits (in week 1-4 weekly, then in weeks 10, 16, 22, 28, 34, 40, 46 and 52; dates varied a maximum of ± 1 week) including application of TcES for 52 weeks and one follow-up visit (in week 78, dates varied a maximum of ± 1 week).

After inclusion patients were randomly assigned to TcES with 0 mA (sham), 150% or 200% of their individual electrical phosphene threshold (EPT) current at 20 Hz.

Patients and technicians who performed kinetic perimetry, as well as full-field electrophysiology (ERG), multifocal ERG (mfERG) and dark adaptation, were blinded to the treatment group for the entire study period. The physicians who performed all other examinations and TcES were not blinded to study treatment because they were responsible for setting the stimulation parameters.

Inclusion Criteria:

• Adult subject with RP (rod-cone dystrophy)
• BCVA 0.02 to 0.9
• Reliable visual field measurements
• Reliable ERG measurements
• Skillful enough to use the device at home
• Able to give consent and take part during the whole study

Exclusion Criteria:

• Diabetic retinopathy
• Neovascularisation of any origin
• After arterial or venous occlusion
• After retinal detachment
• Silicone oil tamponade
• Dry or exudative age-related macular degeneration
• Macular edema
• All forms of glaucoma
• Any form of corneal degeneration that reduces visual acuity
• Systemic diseases that are difficult to control or manage, that could endanger the normal study schedule
• Patients in a permanently poor general condition, which could hinder the regular attendance at control examinations in the clinic
• Forms of mental illness related to the bipolar affective and schizoid-affective disorders, and all forms of dementia
• Simultaneous participation in another interventional study or history of interventions whose effect may still persist

52 weeks treatment, follow-up visit after 72 weeks. AEs were recorded until the follow-up visit at 72 weeks.