ASR subretinal implant for retinitis pigmentosa disappointing

The visual acuity improvements from implantation of the Artificial Silicon Retina (ASR device, Optobionics Corp.) for treatment of vision loss associated with retinitis pigmentosa were "underwhelming," with the 2-year data showing that only 8% of implanted eyes gained 10 letters or more, according to John Pollack, MD.

The device, which is 2.0 mm in diameter and 25 microns thick, is proposed to work by solar power. The light incident on the surface creates a negative charge on the chip. The cells in contact with the chip surface are stimulated and release neurotrophic factors, which results in improved functioning of existing retinal cells. The device is implanted during vitrectomy through a retinotomy, Dr. Pollack, assistant professor of ophthalmology, Rush University Medical Center, Chicago, explained.During a feasibility study at three clinical sites, 20 patients were implanted with the device in one randomly selected eye. Adverse events included migration and fracture of the device and chronic anterior segment implantation, cystoid macular edema, visually relevant cataract, and retinoschisis/macular hole.

"The 2-year data indicated that 16% of eyes had an increase of 10 letters compared with 5% of the fellow eyes, and 11% had a decrease of 10 letters compared with 21% of the fellow eyes," Dr. Pollack reported.

When the investigators evaluated the 1-year data and did subgroup analysis they considered confounding factors of cataract progression and dilated pupils during vision testing, which increased glare, reduced contrast sensitivity, and possibly negatively affected the vision measurements. They found that in eyes that had neither or one confounding factor, 40% of eyes gained 10 or more lines compared with 0% in the fellow eyes.

When they evaluated the 18- to 24-month data, Dr. Pollack reported that the gap narrowed with 40% of eyes that received the device having gained 10 lines of vision compared with 20% of the fellow eyes. In a phase II expansion trial that began in summer 2006 in Mexico City, all 12 patients were pseudophakic and vision testing was done in the undilated state to address the issue of the confounding factors.

In those patients, 8% of implanted eyes gained 10 letters or more compared with 16% of fellow eyes that gained 10 letters or more; 16% of the implanted eyes had a decrease of 10 letters or more compared with 0% of the fellow eyes.

"Implantation of the ASR device has not resulted in significant improvements in Early Treatment Diabetic Retinopathy Study vision. It is possible that the device can be used as an auxiliary power drive or a platform for other forms of subretinal neurostimulation. This intellectual property was purchased by Intelligent Medical Implants," Dr. Pollack said.