Richard L. Windsor, O.D., F.A.A.O.
Pituitary tumors frequently result in a bitemporal hemianopsia. There is usually a loss of the outer temporal field of vision in each eye. Thus, the patient may experience a loss of the right field in the right eye and the left field in the left eye. The field loss may improve or progress after surgery. If the visual field loss does not resolve, it may cause the patient difficulty in navigating in unfamiliar areas. Patients may may bump into things on either side. Since there is some overlap of the remaining visual fields, patients only lose about 30 to 40 degrees off the outer field on each side. Bitemporal field loss is usually less debilitating than hemianoptic visual field loss. Patients, who continue to experience functional problems, may benefit from prismatic visual field awareness systems. Mary is a 64 year old female who developed a bitemporal field loss from a pituitary tumor. Mary experienced difficulty in mobility. She frequently would run into the edges of objects. To aid Mary, bilateral press-on prisms were applied in the circular design similar to the design originated by Dr. Daniel Gottlieb for the Visual Field Awareness System. The same prescription could be fabricated with bilateral Gottlieb Visual Field Awareness Systems. Mary immediately noticed that she could see objects to each side. Scanning therapy was prescribed to further improve Mary's functional abilities.
Photo: Mary's eye wear is fit with bitemporal field awareness press-on prisms.
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.
Visual Field Enhancement Prisms
The Traditional Method
In the past, a straight edged segment of press-on prism was applied to the side of the field loss on both lenses. Success with this method was very limited. Today, however we have a new approach for press-on prism to treat visual field loss.
The New Method
Following the success with the approach developed by Daniel Gottlieb in his Visual Field Awareness System, the same approach may be used in applying a press-on prism. We stamp pokie games the press-on prism material with a round die that cuts a perfect circle. We file the edges to lessen reflected glare off rough points and mount it on the front surface. Unlike the traditional method, we mount the prism only on the lens of the effected side. We want to produce a diplopic image so the patient quickly picks up objects on the side of the field loss as the patient makes natural scanning movements.
The Gottlieb Visual Field Awareness System and In Wave Hemianoptic lens have superior optics to the press-on prism, but as an initial trial lens or as a less costly alternative, press-on prisms have an important place in our treatment of patients. The press-on prism also serves a role in testing patient response and correct prism placement prior to prescribing the Gottlieb Visual Field Awareness System or the In Wave Hemianoptic lens.
Visual Field Awareness System
The application of a prism to enhance visual field has existed for many decades. However, the development of the Gottlieb Visual Field Awareness System has greatly improved our success rates in aiding patients after hemianoptic visual field loss. Gottlieb's novel approach was to abandon the traditional equal prism in each side in a straight line and rather place a small round wafer of base out prism on the side of the visual field loss. The idea is to shift the image into the patient's still functional field as the patient makes natural scanning movements (see the animation below).
Animation Showing How the Gottlieb System Functions
This animation demonstrates how the image missing to the right side is shifted back into the field of view of the patient. A online casino patient approaching this intersection with a right hemianopias is able to better detect the stop sign to the right when the Gottlieb Visual Field Awarenes System is inserted.
The Visual Field Awareness System has been helpful for patients with hemianoptic field loss. The system is mounted in one lens on the side of the loss. It shifts the image about twenty degrees nasally allowing it to be detected within the remaining functional field as the patients makes mild scanning movements. Following fitting with systems, patients will require training by their therapist to learn how to use the system in the real world. Scanning training is also employed to improve the patient's functional use of their remaining visual field.
Visual Midline Shift Syndrome
Visual Midline Shift Syndrome results from dysfunction of the ambient visual process. It is caused by distortions of the spatial system causing the individual to misperceive their position in their spatial environment. This causes a shift in their concept of their perceived visual midline. This will frequently cause the person to lean to one side, forward and/or backward. It frequently can occur in conjunction with individuals that have had a hemiparesis (paralysis to one side following a TBI or CVA). The shifting concept of visual midline actually reinforces the paralysis, by using specially designed yoked prisms that can be prescribed, the midline is shifted to a more centered position thereby enabling individuals to frequently begin weight bearing on their affected side. This works very effectively in conjunction with physical and occupational therapy attempting to rehabilitate weight bearing for ambulation.