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Excerpt:

Artificial Vision for End-Stage Glaucoma: Retinal vs. Cortical ProsthesesAdvanced glaucoma kills the optic nerve and retinal ganglion cells (RGCs), leaving patients blind. Artificial vision (visual prosthesis) aims to bypass such damage. Most existing prostheses target the retina or optic nerve, but in end-stage glaucoma those routes are gone. Instead, researchers are exploring implants that directly stimulate the visual cortex (brain). This article compares inner-retinal (eye-based) versus cortical (brain-based) prostheses for glaucoma blindness.In conditions like retinitis pigmentosa or macular degeneration, the photoreceptors die but RGCs and optic nerve remain intact () (). Retinal implants work here. For example, Argus II (an epiretinal implant) received FDA approval for retinitis pigmentosa in 2013 (). These devices can restore basic light perception and motion detection () (). However, glaucoma is different: the RGCs and optic nerve are destroyed, so a signal from a retinal implant has nowhere to go () (). In novel tests like ORION’s early trial, the goal is to “bypass diseased eye anatomy” altogether by sending electrical signals directly to the brain’s visual cortex (). In short, retinal implants require surviving retinal neurons and an intact optic nerve () (). They are designed for outer-retinal disease (photoreceptor loss) where RGCs still exist () (). Conversely, cortical implants target patients with severe inner-retinal degeneration or optic nerve damage () (). For advanced glaucoma (no RGCs), cortical approaches are the only realistic prosthetic option () ().Inner-Retinal ImplantsInner-retinal prostheses (often called “bionic eyes”) use an external camera (usually on goggles) to capture images and convert them into electrical pulses. These pulses are delivered via a microelectrode array placed on or under the retina (). Epiretinal implants (like Argus II) sit on the retinal surface adjacent to RGCs, while subretinal implants lie beneath the retina among the photoreceptors. There are also suprachoroidal designs (electrodes between the retina and sclera). In all cases, the goal is to electrically stimulate the remaining retinal neurons.Requirements and CandidatesCandidates for retinal implants must have lost photoreceptor vision but still retain an intact inner retina (ganglion and bipolar cells) () (). Typical candidates are those with end-stage retinitis pigmentosa or geographic atrophy (advanced macular degeneration), not glaucoma patients. Glaucoma patients lack viable RGCs, so retinal prostheses generally cannot work for them () ().Surgical Procedure and RisksImplanting a retinal device requires a vitreoretinal surgeon. Procedures like a pars plana vitrectomy (removing the vitreous gel) and attaching the electrode array are needed (). Compared to brain surgery, retinal surgery is less complex. Epiretinal implants are “less complicated and [carry] lower levels of risk during implantation” than cortical devices (). Nevertheless, serious eye-related complications can occur. In a 30-patient Argus II trial, for example, half of the participants experienced device- or surgery-related adverse events over 5 years (). The most common problems were conjunctival erosion (pink eye) and ocular hypotony (abnormally low eye pressure) (). Overall, about 40% of subjects had a serious adverse event (half of which were reversible) (). Systematic reviews confirm that ep

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