Transcleral Photoreceptor Transplantation in a Swine Model of Photoreceptor Degeneration

Abstract

Purpose: : To evaluate the use of a trans-scleral approach for subretinal implantation of a biologic chip in a swine model of photoreceptor degeneration.

Methods: : Intravenous injection of 7.5 mg/kg of iodoacetic acid (IAA) created a selective and inducible photoreceptor degeneration in domestic swine. Two weeks after IAA administration, a transcleral approach was used to subretinally implant five swine with a biologic chip. The chip was comprised of a sheet of allogeneic swine photoreceptor cells, sandwiched between two layers of gelatin and mounted on a polyimide strip (3 x 4 mm). To achieve this approach, the choroid was exposed through a superotemporal scleral flap and cauterized using a diathermy electrode, which also was used to make a mark made on the underlying retina. A pars plana vitrectomy over the white diathermy mark was performed and a localized retinal detachment created in the area with a 39 Ga cannula using balanced salt solution and Healon^®. Mean arterial pressure was lowered to 40-45 mmHg to minimize bleeding while the biologic chip was introduced into the subretinal space though the exposed choroid. The polyimide strip with the photoreceptors was left in place for 5 minutes and then the polyimide strip removed leaving the photoreceptors in the subretinal space. The flap was sutured closed and the implant visualized using the indirect ophthalmoscope. The animals were examined at two weeks with indirect ophthalmoscope. Fundus pictures were taken and fluorescein angiography was performed. At the end of the examination, animals were euthanized and the eyes processed for histologic evaluation at the light microscopic level.

Results: : Using a transcleral approach the biologic chip could be successfully positioned in the subretinal space of the swine with photoreceptor degeneration. Two weeks after implantation, the biological chip was visible, the retinas were reattached and there were no signs of inflammation, infection or hemorrhage

Conclusions: : Transcleral delivery of a biologic chip consisting of a sheet of photoreceptor cells was successfully performed in a swine model of inducible photoreceptor degeneration. The advantage of this transcleral delivery method compared to a transvitreal approach is that larger biologic chips can be implanted into the subretinal space.

Keywords: photoreceptors • retina • transplantation