## 4 Electroceticals--Intelligent Environments
### Artificial Retina  
Nearly 40 million people have blindness worldwide, and another 124 million people are under the low vision category [100; 101; 102; 103; 104; 105]. Researchers are trying to find solutions to solve vision problems. There are two main approaches to improve vision. The first one is retinal prosthesis: within this, two methods are available: epi-retinal stimulation and subretinal stimulation, which involves implanting an electrode array between bipolar cells and retinal pigment epithelium. Compared to epi-retinal implantation, the subretinal prosthesis has an advantage such as closer proximity to the neurons to stimulate and helps in improving visual perception. The second one is the optic nerve, about 1-2 mm in diameter, which serves as a compact conduit for all information in the visual sense. This suggests that stimulating the optic nerve even in a small area would cause greater improvement in the visual sense. This approach offers a safer and easier implementation procedure compared to other techniques. However, focal stimulation and detailed visual perception are difficult due to the stimulating electrodes located over the densely packed optic nerve [100; 101; 102; 103; 104; 105]. Developed technologies by the companies in Table 1, on both the approaches for restoring vision have yielded the best outcomes, authenticated by the implemented clinical trial experiments. Some of the clinical studies (some of them are ongoing) of these implanted devices both near the optic nerve and retina have revealed that they are safe and can be implantable [100; 101; 102; 103; 104; 105]. Although the reported clinical experiments show the efficiency, safety, and compatibility of those, vision with a relatively low spatial resolution of developed implants confirms that further device development is still needed to achieve improved vision and functional vision [100; 101; 102; 103; 104; 105]. One such development is the bionic eye; Boston artificial retina, illustrated in Figure 5 [106; 107; 108]. The device consists of an external transceiver and implanted hermetic neural stimulator. When the patient wears eyeglasses, the camera mounted on the eyeglasses captures an image and sends it to the intelligent controller unit. The controller unit process and encode the image data. Then the encoded data is sent to the implanted device wirelessly, where implanted device antennae receive the encoded data. Then the processing system of the implant decodes the data and induces impulsive electrical signals to stimulate retinal tissue to create artificial vision [106; 107; 108]. Here, the process of sending power wirelessly to the implant requires a compatible and biologically safe method. State-of-the-art research suggests that inductive coupling is the potential and significant source for transmitting power to the implant by assigning one inductive coil as transmitter antennae and the other one as receiver antennae among the two inductively coupled coils [35; 37; 38; 39]. Additionally, a sophisticated electronic circuit is desirable to process, control, and trigger stimulations' exact size and shape. Furthermore, charge-efficient and biocompatible metallic electrodes are required to safely transport stimulating currents to the earmarked tissues. The fabricated electrodes must be compatible in micro/nanosize configurations or planar or semi-curved shapes and should be biologically corrosion resistive and hermetically sealed. The entire electrode system must be capable of working within the intelligent biological environment. An advanced electrode array, mainly in large numbers, is desirable to trigger in a wide area under associated safety conditions. Furthermore, all the advanced circuits with digital control features integrated on a single chip within a small area mean it miniaturized and compatible single-chip design is the most important consideration for the retinal implants along with the device that works under safety regulations [106; 107; 108].