Visual Field Loss
Visual field loss, or loss of peripheral vision, causes a significant limitation of vision. Those suffering from visual field loss will often times bump into objects, miss things to the affected side and even miss half of the food on their plate. Driving is frequently given up and thought to be out of the question.
Help for the Hemianoptic Field Loss Patient
The application of a prism to enhance visual field has existed for many decades. However the development of the Gottlieb Visual Field Awareness System (Dr. Daniel Gottlieb, O.D., FCOVD, FAAO) has greatly improved the success in aiding patients after hemianoptic visual field loss. The approach places a small wafer of base out prism in a round shape on the side of the visual field loss. With this method, as the patient looks to the side of their visual field loss, the image is shifted into their still functional field as they make natural scanning movements.
The Visual Field Awareness System has been helpful for patients with hemianoptic field loss. The lens is mounted in one lens on the side of the loss. It shifts the image about 20 degrees nasally, allowing it to be detected within the remaining functional field as the patients makes mild scanning movements. Along with the prism system therapy is prescribed to assist adaptation and improve scanning.
Hemianopsia is a blindness or reduction in vision in one half of the visual field. Hemianopsia can be caused by conditions such as stroke, tumors and trauma. The cause must always be carefully investigated and diagnosed. Hemianopsia may vary from an absolute loss of all vision on one side to a relative loss where vision is reduced, but not completely missing. Relative hemianopsia may vary from only light or motion detection in the impaired field to just subtle decreases in sensitivity that can only be demonstrated on careful visual field testing. The defect is called a homonymous hemianopsia when the field loss presents on the same side in both eyes. This is typical of stroke, and often causes a physical paralysis, or paresis (weakness) on the same side of the visual field loss. If the stroke affects only the occipital lobe portion of the brain (the part of the brain that processes vision) there will result a homonymous hemianopsia without any other impairment or paralysis.
During the first few months after a stroke or trauma, some improvement in visual fields may be possible, but recovery depends on the extent of the damage. There are no specific treatments to cure the field loss, but today we have optical devices and therapies that help most patients compensate for their visual field loss. These optical systems include the Gottlieb Visual Field Awareness System, the InWave Hemianoptic lens and various press-on field enhancers.
Hemianoptic Mirror Systems
Mirrors have long been used to aid the patients with a hemianoptic field loss. The mirror picks up the image and reflects it into the existing visual field. The mirror provides awareness of objects and movement at the far periphery. The primary problem has been the poor cosmetic appearance.
Rear Surface Mirroring combined with a Gottlieb Visual Field Enhancement System
The posterior surface can be mirrored at the outer edge to provide additional peripheral field awareness. It will not work in some nearsighted corrections, since the angle of the peripheral lens must be very flat. My colleague, Dr. Windsor, began studying the combination of the Gottlieb system and the rear mirror in the early 1990’s, and now Rekindle offers a version of this lens.
Press-on Prism Visual Field Expanders
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. Our success with this method was very limited. Today, however we use a new approach as outlined below.
The New Method
Following our success with the approach developed by Daniel Gottlieb in his Visual Field Awareness System, we now use the same approach when applying a press-on prism. We first stamp the press-on prism material with a round die that cuts a perfect circle. Then 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.
We find the Gottlieb Visual Field Enhancement System optics to be far superior to the press-on prism, but as an initial trial lens or as a less costly alternative, it still has an important place in our treatment of patients.
InWave Prism System
The application of a prism to enhance visual field has existed for many decades. The InWave Hemianoptic Lens uses optical quality prisms to shift the image from the impaired side to the functioning side. The system has been helpful for patients with hemianoptic field loss. The prism is molded in either one, or both lenses on or towards the side of the loss. It shifts the image about twelve degrees nasally to be detected within the remaining functional field as the patients makes mild scanning movements. Along with the prism system therapy is prescribed to assist adaptation and improve scanning.