ASR outcomes still favorable with lengthening follow-up

May 3

- Fort Lauderdale, FL - Follow-up in the first 10 patients implanted with the Artificial Silicon Retina (ASR) microchip now ranges between 2 and 4.5 years. During that time, the device continues to be well-tolerated, and at the last available visit, nine of 10 patients describe improved visual function compared with preoperatively, reported Alan Y. Chow, MD, of Rush University, Chicago.

The ASR microchip is a photodiode-based device measuring 2.0-mm in diameter and 25 microns thick. It is embedded with about 5,000 microphotodiodes and is implanted in the subretinal space 20 degrees from the macula. The first 10 implantations were in the right eye of patients with retinitis pigmentosa; the left eye of each subject was left alone to serve as control.

Patients have demonstrated acuity improvements measured with ETDRS letter charts and grating acuity, and subjectively some have reported improved perception of darkness, contrast, and color. Automated visual field improvement occurred in two patients early after surgery but had substantially regressed by 24 months.

"Visual function has improved in retinal areas both adjacent to and distant from the implant and continue to suggest some neurotrophic rescue effect of the chip," Dr. Chow said.

The safety review showed no evidence of infection, rejection, inflammation, leakage, or neovascularization. However, one patient who underwent phacoemulsification at 1.5 years postimplantation developed a subretinal hemorrhage with a 0.5-mm migration of the implant. The events were thought to be secondary to the ultrasound energy. The hemorrhage resolved spontaneously over about a year without loss of vision.

An expanded Phase II study was initiated in the end of 2004 at three partner institutions with 20 patients implanted.