Bioengineering a better eye: the advent of artificial retinas

Retinitis pigmentosa (RP) and macular degeneration (MD) are two forms of blindness that affect cumulatively over 10 million people in the Unites States. In these particular conditions, the specialized rod and cone cells in the retina of the eye responsible for detecting and transmitting light signals to the brain gradually die off. Without these cells, those images transposed by light to the back of our eyes are never actually sent off for interpretation by the brain. The artificial retina, first FDA approved in 2013, is a feat of biomedical engineering that promises to revolutionize the way we restore sight. In this article, IDTechEx reviews this basis for technology and highlights some expected future developments.

Two aspects of the eye's physiology must be functional for retinal implants in general to work. First, the inner retinal cell layer containing bipolar and ganglion cells must be intact, as these cells typically received information from the degraded outer pigment layer of the retina containing rod and cone cells. Second, the optic nerve must be maintained, as all signals from the retina ultimately converge in the optic nerve to be sent to the brain for interpretation. The two main designs of retinal implants, epiretinal and subretinal, capitalize on the maintenance of the inner retinal layer and optic nerve.

 

 

Epiretinal implants require a microelectrode to be positioned on the innermost surface of the retina. An external camera mounted to glasses worn by the user acquires the image and a connected processing chip transmits the relevant signals to an electrode in contact with the layer of ganglion cells in the eye. These ganglion cells will ultimately convey this information to the brain via the optic nerve. In a 2002 Phase I FDA trial of the Argus-1, patients equipped with the 16-electrode array on their retina were able to detect changes in light and movement such as the waving of a hand.

 

Subretinal implants sit between the outer pigment layer and the bipolar cells. These implants typically consist of a microphotodiode array (MPDA) that receives light signals directly from the environment that are conveyed to bipolar cells first before transmission to ganglion cells and then the brain. A subdermal box containing a power supply is transfixed behind the ear, similar to a cochlear implant. In a recent clinical trial of a 1500-photodiode array, the Alpha AMS, 72% of patients reported a significant improvement in mobility and daily living while 86% reported improved visual acuity and object recognition.

The successor to the Argus-1, the Argus-2® by Second Sight, was FDA approved for patients with RP in 2013. Containing 60 electrodes, this version further enhanced patient discrimination of objects to the level of counting fingers. Addition of more electrodes within an array on the order of 1000's is expected to further restore sight to the level of facial recognition, while miniaturization of the device can be expected to enhance its biocompatibility. Of the 321 patents on this technology, over half were filed within the past decade, further highlighting the great commercial prospects yet to come. To the millions of people who have lost their sight as a result of incurable retinal degeneration, this new and innovative technology has the potential to drastically improve their overall quality of life.

Data source: Google patents