More advanced visual prosthetics can be divided into three major groups. First, there are the devices that use either ultrasound or a camera to sample the environment ahead of an individual and render the results into either a series of sounds or a tactile display. This process is known as sensory substitution because the sense of hearing or touch is substituted for that of sight. From this substitution users are supposed to be able to discern the shape and proximity of objects in their path. The second major form is retinal enhancement. These sensors supplement functions of the retina by stimulating it with electrical signals, which are then converted to nerve impulses and transferred through the optic nerve to the brain. The third major category of visual prosthetic is a digital camera that samples an image and stimulates the brain directly with electrical signals, either by penetrating into or placing electrodes on the surface of the optic nerve or the visual cortex.

Chapter Contents:

• 7.1 Introduction
• 7.2 Anatomy and Physiology of the Visual Pathway
• 7.3 Main Causes of Blindness
• 7.4 Optical Prosthetics - Glasses, Thermal Imagers, Night Vision
• 7.5 Sonar-Based Systems
• 7.5.1 Some Existing Systems
• 7.5.2 Issues with Sonar-Based Systems
• 7.6 Laser-Based Systems
• 7.7 Sensory Substitution
• 7.7.1 Auditory Substitution
• 7.7.2 Electrotactile and Vibrotactile Transducers
• 7.8 GPS-Based Systems
• 7.9 Visual Neuroprostheses
• 7.9.1 Historical Perspective
• 7.9.2 Potential Sites for Visual Neuroprostheses
• 7.9.3 Components
• 7.9.4 Worldwide Research Activity
• 7.9.5 Subretinal Implants
• 7.9.6 Epiretinal Implants
• 7.9.7 Alternative Implants
• 7.9.8 Optic Nerve Stimulation
• 7.9.9 Visual Cortex Implants
• 7.10 The Future
• 7.11 References

Inspec keywords: touch (physiological); brain; neurophysiology; bioelectric phenomena; biomedical ultrasonics; hearing; visual perception; biomedical electrodes; prosthetics; eye

Other keywords: digital camera; ultrasound technology; electrical signals; visual cortex; brain; hearing sense; touch; optic nerve; sensory substitution; visual prosthetics; nerve impulses; retinal enhancement; electrodes

Subjects: Sonic and ultrasonic radiation (biomedical imaging/measurement); Anatomy and optics of the eye; Sonic and ultrasonic applications; Prosthetics and orthotics; Audition; Bioelectric signals; Sonic and ultrasonic radiation (medical uses); Prosthetics and other practical applications; Electrical activity in neurophysiological processes; Psychophysics of vision, visual perception, binocular vision; Mechano- and chemio-ceptions