gms | German Medical Science

Purpose: The Prima system, including a wireless subretinal photovoltaic microchip, is designed for restoration of central vision in patients blinded by retinal degeneration while preserving the residual peripheral field. Minimal invasive surgical implantation technique was designed to make sub retinal implantation as safe as possible.

Methods: A prospective single-center study of feasibility and safety in 5 patients with no central foveal perception and residual peripheral visual acuity ≤20/400 in the treated eye due to geographic atrophy. For each patient, the first step was to determine the location of the main PRL in the periphery by microperimetry to plan surgery accordingly. The retinotomy was made distally from this area. Surgical technique included a complete vitrectomy, detachment of the posterior pole with subretinal BSS injection, achieved completely in 4 cases with manual dissection of the atrophic macula, creation of a 2.2 mm retinotomy for the 2x2 mm microchip, insertion of the microchip under the macula with vertical forceps, injection of perfluorocarbon liquids to stabilize the macula, finally exchanged with either silicone oil or gas. No photocoagulation was done to avoid increasing the lesion of the optic fibers.

Results: In all 5 patients, the microchip was successfully implanted under the macula and remains stable, with a follow-up reaching 18 months in the first patient and 12 months in the last patient. In 3 patients the microchip was placed into an optimal position – centrally and close to the fovea. In 2 patients the microchip was within the scotoma but in suboptimal positions – one in the choroid and another paracentral. The first patient operated under local anesthesia, moved the head when the vertical forceps and the chip were being maneuvered under the retina, ending up with a subretinal bleeding masking the implantation area. The chip was pushed under the retina without adequate visual control and ended up under the retinal pigment epithelium. In the fourth patient, the chip was placed under the fovea and gas was used as final tamponade. Control on postoperative day showed the microchip had shifted slightly to the inferior margin of the scotoma. Using totally opaque feasibility study glasses, all 5 patients perceive white-yellow patterns with adjustable brightness in retinotopically correct locations, within previous scotoma with no foveal perception. The 3 patients with optimal placement of the subretinal microchip recognize complex patterns, letters and sequence of letters, demonstrating visual acuity elicited from the central atrophic area with no pre-surgery foveal perception, to reach 20/460-20/550 post implantation of PRIMA in this central atrophic zone, just10-30% below the theoretical resolution limit for this pixel size (20/420). Without the system, all patients had the same visual acuity as in their preoperative vision.

Conclusions: Wireless photovoltaic microchip PRIMA can be safely implanted under the atrophic macula and restore useful central visual perception, while preserving peripheral vision. Improvements of surgical tools such as using a specifically designed delivery system may help further to make implantation easier and avoid suboptimal positioning of the microchip. A larger multicenter European pivotal study is planned to further evaluate the PRIMA system in atrophic dry AMD.