The purpose of this study is to look at the safety and effectiveness of CNTF implants on vision in persons with retinitis pigmentosa, Usher type II & III, and Choroideremia. This research is being done because there are no effective therapies for people with these retinal degenerations. They are genetic disorders that affect one's ability to see at night, and later cause tunnel vision and loss of central vision. Retinal degenerations affect the retina, a light sensitive layer of cells in the back of the eye. Slowly over time, these cells die and cause permanent loss of vision.

The implant is a small capsule that contains human retinal pigment epithelium cells. These cells have been given the ability to make CNTF and release it through the capsule membrane into the surrounding fluid. In this study, two different CNTF dose levels will be used: a high dose and a low dose in one eye, as well as a sham (or placebo) surgery in the other eye.

This study will involve about 18 visits over 2½ years for specific tests of the participant's vision and health. These visits may include visual exams, blood draw for laboratory testing, brief medical history and exam, and occasionally a questionnaire (survey), in addition to the visit for the surgical procedures. The primary effectiveness outcome for this study will be a visual field score one year after the implant surgery. There will be about 12 centers participating in this study, and up to 60 people enrolled, across the US. Each participant joining the study who has completed initial screening will then be scheduled to have a brief surgical procedure performed on each eye, one of which will include a very small cell-filled implant. Follow-up visits for repeat assessments will be required regularly to determine if the implant being tested is safe and effective for use to treat retinitis pigmentosa (RP).

Study inclusion / exclusion criteria:

Criteria for patients to qualify for the study include, but are not limited to:

• Over 18 years of age, and less than 65 years of age
• Diagnosis of retinitis pigmentosa, Usher Syndrome Type 2 or 3 or Choroideremia
• Visual acuity no worse than 20/63
• Experience with at least two full threshold Humphrey Visual Field 30-2 tests, one completed within the year prior to enrolling in this study

The following criteria will exclude patients from the study:

• Pregnant or lactating females, or females planning to become pregnant during the study or not using an acceptable method of contraception.
• Retinitis pigmentosa caused by a classic syndrome, including Usher Type I
• Other eye diseases including advanced cataract.
• Chronic systemic disease requiring continuous treatment with systemic steroids, immunosuppressive medications or insulin.