21.1  Concepts of Functional Vision and Rehabilitation

Although there are a variety of technological approaches to providing an individual with prosthetic vision, when the technology allows the individual to reverse contrast, this feature may enhance the individual’s ability to detect objects and the like. Many patients who utilize a closed circuit television (CCTV), for example, prefer to do so by making the letters white and the background black (that is, by reversing the contrast of the monitor). This technique could be applied to mobility, for finding a doorway out of a well-lit room, if the individual using prosthetic vision reversed contrast to show a bright door opening in a dark wall.

The foregoing examples described potential enhancements to orientation with no descriptions of benefits to mobility, because the current prosthetic vision technology is not sufficient to replace or eliminate the need for a long cane or a guide dog for independent travel in unfamiliar environments. The point is that ultra-low vision can have a positive impact on functional orientation but not on mobility in novel environments.

Today’s prosthetic vision may be potentially safe enough for an individual to use it as their primary source of mobility information (no cane or guide dog) indoors in a controlled and familiar space or when locating furniture or objects with high contrast. A “controlled space” is an indoor environment in which changes in elevation (stairs) are not present or their location is known, and in which furniture and other room elements maintain the same location over time. Travel in unknown and/or complex environments (crossing the street or walking in a shopping mall) requires the use of a long cane or guide dog. In such a situation, prosthetic vision can be used as a supplementary source of information to enhance the individual’s orientation while other sensory information (audition, tactual) is combined with primary sources of information for mobility: the long cane or guide dog.

21.1.2  Application for Activities of Daily Living

Because prosthetic vision provides very low levels of visual acuity, activities of daily living (ADLs) that require detailed vision (sewing, reading, or the recognition of facial features) are not envisioned as being amenable to prosthetic visual rehabilitation until the level of resolution the technology provides has been substantially improved. The opportunity presented by the current technology, which allows users to perceive high contrast can be of benefit with a variety of ADLs, including personal care and personal management. For example, in the area of personal care, the ability to identify toothpaste on a toothbrush might be accomplished with the use of high contrast (green toothpaste on a white-bristled toothbrush). Visually locating soap or a shampoo bottle in a bathtub may be possible with high contrast. The ability to apply lipstick may be enhanced with ultra-low vision. The ability to visually sort darkand light-colored socks, to identify a white shirt from a dark-colored shirt may be possible with prosthetic vision. The use of contrasting colors in the kitchen could prove to be beneficial for people with prosthetic vision, who may be able to

Fig. 21.2  Effect of contrast on visibility: a dark placemat and a light dish

differentiate milk from juice or mayonnaise from ketchup in the refrigerator. The use of high contrast between a dark placemat and a light-colored dish can enhance a client’s ability to locate the dish, as illustrated in Fig. 21.2.

21.1.3  Patient Lifestyle and Expectations

Early chapters of this book concentrated on the visual system to the exclusion of personal history. As rehabilitation specialists, we think of vision in the context of the person, their history, lifestyle, expectations, and acknowledge that these personal elements influence the way vision is used. Consider two patients who have the same clinical vision status (visual acuity, contrast sensitivity, visual field); one patient uses a cane and minimizes the use of their remaining vision, and the other travels without a cane, and utilizes optical equipment to read street signs and view traffic lights. Individuals who maximize the use of their remaining vision (light perception) prior to implant tend to have the best prognosis for integrating prosthetic vision into their lifestyle and to experience more benefits after implantation.

The management of patient expectations is a key element to successful functional outcomes with prosthetic vision and must be considered part of the rehabilitation process. Patients want to know how their life will change or improve with prosthetic vision. Will prosthetic vision resolve their functional problems? Research on the most common functional problems in mobility clearly shows that managing illumination (light adaptation, low-light environments), detecting changes in elevation such as drop-offs (curbs, stairs), and crossing the street are three of the most common problems for patients with low vision [4]. Our experience with prosthetic vision suggests that these leading low vision mobility

problems may not be addressed by the current technologies. The implant wearers we have seen at the time this chapter is being written are, in the context of O&M, quite similar. They are all independent travelers who use some combination of long cane, guide dog, and/or remaining vision. They travel in familiar and unfamiliar areas, ride public transportation, and do not report a serious limitation to their independent travel because of the loss of vision. Because the prosthetic vision systems we have worked with provide ultra-low vision, we have not identified anyone for whom prosthetic vision has been sufficient to replace the long cane or the guide dog when walking in unfamiliar areas. Until the technology improves visual acuity and visual field, prosthetic vision is viewed as an additional travel aid, an enhancement to travel, specifically orientation, rather than a substitution system that would supplant the primary travel aid. Therefore, specialized instruction from properly trained rehabilitation professionals will benefit a prosthetic vision program.

21.1.4  Congenital and Adventitious Vision Loss

We assume there is an interest in offering prosthetic vision to those with congenital blindness. There is a significant difference between the visual abilities and the psychological adjustment process of someone with adventitious vision loss who has had his sight restored (cataract extraction, corneal transplant) and an adult with congenital vision loss who has been provided sight for the first time as an adult. Personal accounts such as the experience of Mike May, described in the book Crashing Through [7], show that clearing the optical pathway does not result in an immediate improvement in functional vision for someone who is congenitally blind. In fact, the more common experience involves a sense of being overwhelmed and confused [6]. It is important to recognize that an individual who has lived as a blind person does not suddenly benefit from visual input. If the patient has a congenital vision loss, a significant period of adaptation, learning to interpret this novel sensory input and time to develop a visual memory, will be required. If the patient lost vision later in life, the age when it was lost, their ability to use low levels of vision as their vision gradually decreased, the primary learning modality for gathering information from the environment (visual, tactual, auditory), and the amount of remaining visual memory are a few of the issues to consider before implantation. These issues may also become a part of the screening and selection process for those who will participate in any type of prosthetic vision rehabilitation program because different strategies may be needed when providing rehabilitation training to these individuals.

Another often repeated description from those who gained sight as adults involves the amount of effort required to process visual input. Mike May describes the need to close his eyes to process information and to feel calm [7]. As revealed in May’s experiences, there are unknown challenges that await the patient who gains sight after leading the life of someone who is congenitally blind.