The word amputation is commonly associated with limbs, leaving other forms of amputees overlooked. Due to increasing cases of diabetes and other chronic diseases, an estimated 93 million adults in the United States are at high risk for serious vision loss. However, bionic eyes provide the promise of artificial vision to those who are visually impaired who could see before. Retinal and cortical visual prostheses are likely to restore partial sight to patients who lose their eyesight to neurodegenerative diseases, such as retinitis pigmentosa.
Bionic eyes are still relatively new, with the first rudimentary version, created by Australian company Bionic Vision Australia, reported in 2012, and was for a patient with vision loss due to retinitis pigmentosa. The patient reported being able to see light but being unable to view their environment. Since then more advanced technologies are being developed and have been implanted.
However, at this time, bionic eyes are only able to offer partial eyesight, such as allowing them to have glimpses into their environment or enabling them to view abstract images. Also, due to bionic eyes being a more recent innovation, the long-term effects of a bionic eye are still unknown. Nonetheless, bionic eyes have been an improvement in the quality of life for amputees and allow them to better interact with the world daily.
There are also many innovations and improvements of bionic eyes being researched. For example, Gianluca Lazzi and his colleagues at the University of Southern California have made progress in developing a system to mimic the complexity of the retina. Their model imitates the many functions and positions of the millions of nerve cells within the eyes. They are further pursuing mimicking the behavior of the neural systems to gain a better understanding of the neural system itself. Lazzi and his colleagues also seek to increase clarity and color vision in future retinal prosthetics. To achieve this they have tested patients with epiretinal implants to better understand the mechanisms of color encoding due to electrical stimulation of the retina.
A current epiretinal prosthetic, also known as a retinal prosthetic or epiretinal implant, functions through capturing light and converting it into an electrical pulse which stimulates the innermost layer of the retina, retinal ganglion cells which are the most likely to remain intact in the early stages of degeneration. The prostheses use an array of stimulus electrodes to activate the neurons to produce a series of phosphenes. The phosphenes allow patients to independently perceive objects and their surroundings in an unknown environment.
In clinical studies of patients who used an epiretinal prosthesis, electrical stimulation has been able to allow for variation in color perception, suggesting that color could be encoded in retinal prostheses. During a different study, it was discovered that when phosphene brightness was sustained the increased stimulation allowed subjects using an Argus II implant, an epiretinal implant, to perceive blue-tinted colors.
Another challenge that researchers face when creating a bionic eye is the difficulty to replicate the natural form of the eye, specifically the concave structure of the retina. Typically in a bionic eye, one of the reasons for it only being able to grant partial vision is that the artificial retina is often flat, leading to less light being captured. However, researchers at the Hong Kong University of Science and technology have devised a method for placing photo sensors on a hemispheric artificial retina. A curved retina is important because natural light only hits the retina after passing through a curved lens. A hemispheric artificial retina allows for a wider field of view, higher responsiveness, and higher resolution comparable to that of the human eye. This new artificial eye is an incredible innovation due to its sensory capabilities being alike to those of the natural eye.
Hong Kong University of Science and Technology’s new artificial eye functions on the basis that perovskite, a conductive and light-sensitive material used in solar cells, can be used to make thin nanowires that are several thousandths of a millimeter in length. The nanowires replicate the eye’s photoreceptor cells, which are typically long and thin. To solve the difficulty of the curved retina, they formed soft aluminum foil into the desired hemispherical shape. This aluminum was then converted into an insulator known as aluminum oxide through an electrochemical process.
The curved artificial retina was then incorporated into an artificial eye which had a curved lens in the front. This artificial eye also had another interesting innovation in that it mimicked the aqueous humor of the natural eye by filling its artificial eye with an ionic liquid. The ionic liquid is important because when the nanowires generate charges it will be exchanged with ions, allowing the perovskite nanowires to detect light and send signals to the external image-processing unit.
This new artificial eye has the capabilities to process patterns of light in 19.2 milliseconds, half the time required by the natural eye, along with producing images that had a greater resolution than those generated by a flat image sensor. However, the artificial eye did not have as great a field of view as that of the human eye, with the artificial eye only having a 100 degrees field of view while the human eye has a field of view of 130 degrees.
Overall, bionic eyes are a new, promising field that only will have more added innovation. This has the capabilities to not only improve the vision to those with vision loss but possibly be transferred to give AI improved vision. Although there are still many limitations to the bionic eye in the coming decades there will likely be a more tangible and practical application of the bionic eye.