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Towards the bionic eye

Fear of blindness is deeply rooted. The rapid growth of older populations brings the consequence of degenerate eye disease. Cataract, glaucoma and macular degeneration impair quality of life and where blindness ensues, reduces life expectancy. The inherited retinal dystrophies such as retinitis pigmentosa lead to photoreceptor degeneration. Significant numbers are blinded from improvised explosive devices in military conflict. Surgical treatment of cataracts is relatively cheap and highly effective, impaired only by access to facilities. Despite early detection and aggressive treatment, glaucomatous optic neuropathy still impacts the aged population. Advances in delivery of antibodies targeting vascular endothelial growth factor have been revolutionary in slowing or improving vision in patients with age-related macular degeneration. Despite these strategies, there remains a significant population with drastically impaired vision. The failure of these therapies has stimulated the development of the bionic eye. Initial attempts at synthetic vision started 50 years ago and have developed into multiple approaches internationally. The paper by Lewis et al. in this edition reviews the development and application of bionic strategies to restore a form of useful vision to patients with blindness from retinal degeneration by implantation of a retinal or cortical stimulating array receiving signals from a camera. Bionic eye implants have shown sustained and improving vision with continued stimulation. Progress in direct stimulation of the visual cortex through different models requiring invasive neurosurgery has not yet achieved equal function to the eye prostheses. All approaches rely on neuroplasticity to present a useful image of phosphenes – points of light. Stimulating the inner retina and optic nerve in an intact eye where photo receptors have degenerated provides the prospect of much better image generation through the inherent processing anatomy of the retina compared with direct stimulation of the visual cortex where both eyes are lost or where extensive loss of ganglion cells leads to blindness in glaucoma. Current methods involving invasive neurosurgery have to be balanced between morbidity, cost and effectiveness. At this stage, regulatory approval for the trials of cortical prostheses has not yet been given. Bionic ear implantation has been a triumph of modern rehabilitation and achieves results with a far smaller stimulating array of electrodes than required for visual prostheses. Array implantation in the eye involves either complex and complication-prone surgery by direct retinal stimulation or alternatively with less invasive supra-choroidal implantation of an array beneath the scleral wall which is technically easier and carries fewer complications. Similarly, the success of implanting device of either ocular or cortical types depends on careful psychological screening, intensive rehabilitation of the patient and longevity of the device. Numerous strategies involving biological and electrical devices are in development in a multinational effort. However, even with limited results at this stage, the rapid advances through diverse technologies are helping to better define selection and surgical application.