**8. Conclusion**

*Prosthesis*

connections of the retina [32]. Four important parts of the eye in visual perception are the lens, cornea, retina, and retinal pigmented epithelium. Any defect in one of these parts can cause blindness. Several intractable blinding conditions are due to retinal damage, the most common type being retinal degeneration. This can be broadly classified into two categories: photoreceptor rod degeneration like retinitis pigmentosa, and macular photoreceptor cone degeneration like age-related macular degeneration (AMD). The prevalence of rod degeneration is estimated to be about 1 in 3500 around the world. It is also estimated that 2 million Americans above the age of 55 have AMD, with another 7 million being pre-symptomatic [33]. Retinal prostheses try to reactivate the residual circuitry in a blind patient's retina to produce a synthetic form of usable vision. Using an array of stimulus electrodes or lightsensitive proteins, the neurons in the degenerate retinal network are activated to elicit a series of light percepts termed "phosphenes." This acts as independent spatial

The type of prosthesis is chosen based on the condition of the subject's vision. Different types of retinal prostheses include epiretinal prosthetics, in which the device is implanted into the vitreous cavity, and subretinal prosthetics, where the device is implanted in the potential space between the retinal pigment epithelium and neurosensory retina to stimulate the outer retina. Epiretinal prostheses like the Argus II include an imaging device like a camera which transforms visual information into patterns of electrical stimulation administered to viable retinal neurons. In the case of subretinal prosthesis, a micro-photodiode array (MPDA) is implanted between the retinal pigment epithelium and bipolar cell layer, which enhances vision in patients with RP and AMD. It can be considered as a replace-

Epiretinal and subretinal devices have their advantages and disadvantages. Advantages of subretinal devices include a lower current requirement and the lack of a need for mechanical fixation due to its proximity to the visual neurons. Disadvantages include the limited subretinal space and the increased risk of thermal damage to the neurons due to heat dissipation in the vitreous humor [36]. Advantages of epiretinal devices include reduced thermal damage to the neurons, a reduced number of electrodes, and a flexible procedure for subsequent surgeries. Disadvantages include increased electrical current requirements and adhesion of

the device to the inner retina, which is more technically challenging [37].

A maxillofacial prosthesis is an artificial replacement for facial features to restore oral functions such as swallowing, mastication, and speech. There are numerous causes which can be congenital, traumatic, or disease-borne in nature. Maxillofacial prosthetics are a better option than conventional surgery when multiple procedures would be required. Also, surgical reconstruction may be limited by insufficient residual tissue, vascular compromise after radiation, age, the inadequacy of the donor site, or patient preference. Rehabilitation with maxillofacial prosthesis aims to restore an effective division between oral, nasal, and orbital cavities and gives faster reconstructive possibilities simplifying the post-surgery period and recovering an adequate patient lifestyle. Maxillofacial prosthetics are a subspecialty of prosthodontics which is a collaboration of ear, nose, and throat specialists, plastic surgeons, oral surgeons, and radiation oncologists in the case of cancer patients. Thus, it is a multidisciplinary branch which focuses on improving quality of life by preserving residual structures, restoring oral functions, and

percepts in their visual field, restoring a crude form of vision [34].

ment for lost photoreceptors [35].

**7. Maxillofacial prostheses**

improving esthetic appearances [38].

**6**

Throughout history, prosthetics have consistently improved on the degree of functional restoration possible for amputees and those with lost function. This improvement in their ability to perform ADL has led to improvements in quality of life. Recent trends in technology such as microprocessors, robotics, manufacturing, and biomechanics promise to improve both the functional and esthetic aspects of prosthetics, giving them a lifelike quality in both form and function. In this book, we explore some of these cutting-edge developments and how they will lead to better devices, ranging from limb replacements to retinal and maxillofacial prostheses. Future progress will be determined largely by patient needs, with economic restrictions leading to a desire for lower-cost yet reliable devices. Technological developments in neighboring fields such as aerospace and computer technology can lead to further innovative designs, making the future of prosthetics a promising one.