Spatial Rehabilitation Using Field Enhancement Prism Systems
(Reprinted from the NORA Newsletter)
Jannie Shapiro, M.Ed., Coordinator Vision Rehabilitation Services The Rehabilitation Center New Haven, CT
It is not uncommon for a visual field loss to occur as a result of a CVA or traumatic brain injury. The course of treatment, particularly for a homonymous hemianopsia, is the use of a temporary Fresnel expanded field prism placed base-out on the lens of the affected side. During the neuro-optometric evaluation, the doctor can determine the need for such treatment and the appropriate placement of the lens. However, in order to ensure success for the patient, training should be implemented to develop scanning techniques for traveling and increased field awareness.
The training program can be provided by an orientation and mobility instructor or therapist. Most importantly, the training should be progressive, bringing the patient from an understanding of how the prism works to the point where he or she can effectively and safely travel while wearing the prism system. During the training sessions, the instructor can also determine if the placement of the Fresnel prism is functional and effective for the patient.
Initially, pre-training issues should be discussed and demonstrated. These issues include scanning, the blind spot created by the line between the carrier lens and the Fresnel prism, and safety issues (ie., not relying on the prism to give information regarding distance, height and speed of movement of an object.)
Training should then be provided in a static-setting with the goal of moving on to a dynamic one. While the patient is seated, the trainer should demonstrate the displacement effect that occurs when view through the prism. Activities of scanning should be provided to demonstrate the functional effects of displacement. The patient should also be asked to reach for objects seen through the prism in order to develop accurate eye hand coordination.
The next step should involve a demonstration of increased functional field awareness. The patient is asked to stand in a hallway. The instructor walks past the trainee on his affected side, asking the patient to indicate when he can see the instructor. The patient should be looking straight ahead. Next, the patient is asked to look into the prism and repeat the same activity. A comparison of when the instructor was detected is then made, demonstrating the effectiveness of the prism for quick object localization.
The next stage of training involves movement. The patient is asked to walk in the hallway while scanning in and out of the prism. He must try to locate objects in the hallway and describe them. If the patient is unsteady, sighted guide (holding on to the elbow of the trainee) may be used initially. As the patient becomes more comfortable, increasingly complex environments and situations can be introduced by the instructor. The instructor can walk alongside the patient, then move diagonally in front of him from the affected side to test and improve reaction time. The patient can be asked to reach out and touch the instructor's hand in different positions as he walks to improve dynamic scanning techniques. Outdoor training can also be provided, with reminders that the prism should not be used to detect approaching cars, stairs, or curbs.
As the patient becomes more comfortable and efficient in the use of the expanded field prism, this treatment approach should prove to be successful and long-lasting for him. After this temporary system has been determined to be successful a permanent mounted prism system can then be prescribed.
This training approach is based on "Functional Evaluation & Training Techniques in-the Use of Fresnel Prisms for Individuals With Restricted Visual Fields" by Duane Geruschat, PhD & Audrey Smith, PhD.