21.2  Evaluation and Intervention with Prosthetic Vision

21.2.1  Evaluation

The process of rehabilitation always begins with an evaluation. The evaluation of prosthetic vision should begin with an assessment of functional vision [2, 8, 9]. The typical functional vision assessment is hierarchical and begins with evaluating the ability to respond to a light source, determining if the patient can localize, fixate, track, and scan the light. This is followed by an assessment of visual motor skills then higher order perceptual skills (color identification; threeand two-dimensional shape recognition; and symbol, letter, and word recognition).

The standardized functional vision assessment is followed by a comprehensive evaluation of the use or non-use of vision for mobility [4], personal care, and/or personal management. A few examples of this assessment include the ability to detect changes in contrast of open doorways, the ability to locate windows, to visually trace the lights in a hallway, and the ability to identify the location of a white napkin on a dark table.

Information gained from such assessments can be useful for developing an intervention program. For example, let’s assume one patient with no residual vision travels independently without a long cane or guide dog, but only in her home and within a fenced back yard. The patient has small children and frequently steps on or kicks toys and bicycles that are left on the floor or grass. During the evaluation it is determined that the goal for this patient is to improve her ease of travel in the home and around the yard through improving her ability to locate high-contrast objects. Prosthetic vision (form perception) could enhance this patient’s life by reducing the frequency with which she kicks her children’s toys. The intervention may involve teaching the patient scanning techniques to locate obstacles. It may also be necessary to teach the patient how to interpret prosthetic vision, to essentially determine the identity of the low-resolution images her prosthetic vision provides. This patient’s vision rehabilitation program will emphasize integrating prosthetic with other sensory information to reduce the mental effort that occurs when she experiences a new type of sensory input.

Another patient with minimal residual vision travels independently on public transportation using a long cane supplemented by light projection. Prosthetic vision for this patient may provide form perception and the ability to differentiate areas of high contrast such as the sidewalk (light) from the pavement of the street (dark). This patient would be introduced to the same concepts that are currently taught to someone with severe low vision. Specifically, instruction would address the issue of when it is safe to use vision only and when vision is only safe to supplement the use of the long cane. This is one of the more challenging skills to acquire. It is difficult to always know when vision alone can be the primary modality and provides sufficient information for making decisions about safety.

21.2.2  Intervention

As the technology improves, allowing for sharper visual acuity, contrast sensitivity, and an increase of peripheral visual fields, we expect that some type of instruction to enhance the use of prosthetic vision will be beneficial. We assume there would be two distinct approaches to instruction, one approach for patients who present with congenital blindness (no visual memory) and an approach for patients who lost vision later in life.

The descriptions from prior decades on the effect of adult onset of vision could be instructive for anticipating and understanding the challenges to be faced by an adult with late onset of vision [3]. We would expect to observe a patient with limited ability to comprehend what they were seeing. The work of Mary Anne Frostig and Natalie Barraga during the 1960s [1], specifically their instructional procedures that follow the process of visual perceptual development, would be a useful place to begin instruction.

The large body of literature on instructional strategies for children with low vision, as well as the literature on visual perceptual instruction that has evolved during the past 40 years, provides useful concepts and instructional sequences that could be adapted for an adult population. Since the adult patient with congenital blindness and adult onset of vision is functioning visually at an earlier developmental level, materials written for children may prove to be useful. The American Printing House for the Blind has a collection of materials such as Bright Sights that are designed primarily for children with low vision. The materials provide lesson plans of sequential lessons as well as assessment tools to monitor progress. For use with adults, the materials and lessons would need to be modified to be age appropriate. Isolating the visual system in the early developmental stages before integrating visual information through a multisensory approach has been demonstrated to be effective with young children. Experience will be required to determine if this same approach would be useful for adults with congenital blindness and adult onset of vision.

For adults who have visual memories, early visual developmental skills should still be present or could be re-acquired fairly quickly. Intervention strategies for these adults could include the introduction of specific visual skills such as establishing a consistent response to a given visual stimulus (type of light source), systematic scanning to localize objects, fixate on the object, tracking and shifting gaze between objects, as well as some perceptual training to learn to (re)interpret the visual world. Instruction may also involve teaching low vision skills such as scanning to define the borders of an area, practicing the important ability of being systematic, and scanning for objects in the direction perpendicular to their primary orientation [4].

Localizing and fixating are specific techniques that can be impaired by ocular pathology. We do not know the effects of prosthetic vision on these skills. There may be a need to introduce eccentric viewing to improve visual clarity, as well as the concept of turning the head to an eccentric position to improve visual ability.