While transplants of human corneas and artificial intraocular lens implants are commonplace, the back portions of the eye — in particular, the optic nerve and retina — have not lent themselves to transplantation.
The retina consists of 12 layers with an enormous number of photoreceptors (120 million rod cells and 6 million cone cells) connecting to over a million neurons, each passing through the optic nerve and wired to a particular place in the brain. The retinal pigment epithelium (RPE) Is basically a supporting tissue under the retina, supplying the rods and cones with nutrition and whisking away waste products.
In a potentially major step forward, researchers from the University of Southern California ( Ophthalmol Ret 2020; 4:264) have successfully developed and implanted a layer of bioengineered retinal pigment epithelial cells into the eyes of 15 patients with age-related macular degeneration (AMD).
In the experiment, 3.5 x 6.25 mm single-cell layer sheets were folded and inserted through a 1-mm opening from the outside of the eye in. The operations, which took two to three hours each, were not designed to restore lost vision, just to demonstrate that the tissue could be implanted successfully and survive over an extended period.
This approach may be more successful than previous implantation attempts which tried to inject cells under the retina. In general, those attempts were limited by the failure of the injected cells to “line up” properly under the photoreceptor layer.
The study authors caution that we’re still a long way off from preventing or restoring vision loss from AMD using this technique, but the successful implantations brings the possibility a lot closer!