Prisms Restore Lost Peripheral Vision

eople with a form of partial partial “ghosts.” (See diagram, fac- chief of the low-vision service at the vision loss known as homony- ing page.) The ghost images act as Ohio State University College of P mous hemianopia now have a a cue. “When an object of interest is Optometry. “The key reason is that potentially better way to cope with detected through the prisms it the person doesn’t have to make an their disability: special eyeglasses catches his attention and he can eye movement into the prism to get equipped with prisms that allow the turns his head and eyes toward it,” any benefit. It’s always right there; wearer to avoid obstacles. The Dr. Peli explains. you are always getting that informa- glasses are also less expensive than tion.” Dr. Flom recently prescribed some other options for people with Potential benefits her first pair of prism glasses to one hemianopia. Soon, eyeglasses with People with hemianopia often col- of her patients, a wheelchair-bound prisms may also help people with lide with doorframes, furniture, and stroke survivor with hemianopia tunnel vision due to glaucoma and other people. The prism glasses retinitis pigmentosa. offer a way for people with homony- How you are fitted mous hemianopia to navigate the The first step in taking advantage of Out in the field world a little more safely. A key fea- this new technology is being fitted Homonymous hemianopia is the ture of the system is that the prisms with temporary stick-on prisms to loss of half of the visual field of both are positioned to pick up images establish whether or not it will work eyes, creating a “blind spot” on the from the person’s blind spot no mat- for you. Once you are sure the left or right side. Normally your field ter what direction he happens to be system is doing what it should, two of vision consists of central vision looking. higherquality prisms can be cut and (what you see straight ahead) as installed permanently in a pair of well as your peripheral vision How well does it work? eyeglasses. The two permanent (objects that you perceive “in the Dr. Peli has fitted many of his prisms cost about $300 each. corner of your eye’?. Causes of patients with the system. He recent- Patients can also continue with the hemianopia include stroke and trau- ly described his results with the first inexpensive stick-on prisms, Peli matic brain injury. 12 of those patients in a study in the says, although they arehajd to keep September 2000 issue of Optometry clean and fall off periodically. How it works and Vision Science. All patients but The system consists of a pair of one significantly expanded their Other options plastic prisms mounted on the top visual field. Other optometrists have Eye doctors who treat low vision and bottom edges of one lens in a begun to offer the device. “I think sometimes install flat “sector pair of eyeglasses. The prisms pick this is potentially very valuable for prisms” on both lenses of a pair of up images from the impaired por- patients,” says Roanne Flom, OD, eyeglasses. Binocular sector prisms tion of the person’s vision and direct them into the still-functioning part of the visual field. The prism Eli Peli’s Prism Glasses glasses enable people with hemi- anopia to expand their effective visual field by up to 20 degrees. They were developed by Eli Peli, OD, an engineer and optometrist who is a senior scientist at the I Schepens Eye Research Institute in I I Boston and an associate professor I - A person with right of ophthalmology at Harvard I hemianopia can see Medical School. I nothing on the other I side of this line Each prism is about a third of an Glasses with prisms installed in the upper I inch thick. Because the prisms lie and lower portions of one lens enable ?- Prism glasses make it possible near the top and bottom edges of someone who has lost half of their visual to see objects this far into the field {hemianopia) to see partly into “blind spot”--about 20 degrees the lens, the images they project are their “blind spot. ” are supposed to function much like but people adapt to it the side view mirrors on a car, mak- quickly. “In most ing things visible that lie outside the patients, if they try the driver’s peripheral vision. system they are success- In practice, optometrists have had ful,” Dr. Gottlieb says. limited success with binocular sector In the Peli system, the prisms. The glasses, explains Dr. Peli, double vision occurs in merely shift vision to one side-typi- the peripheral vision. cally about 10 degrees. “I’ve always This is because the per- been pretty skeptical about what son does not look direct- binocular sector prisms were sup- ly into the prisms. Dr. posed to do,” Dr. Flom adds. “They Peli asserts that this is only provide any benefit if the per- less disorienting than son makes an eye movement toward diplopia introduced into the blind side. And even then, the central vision. However, Partial ghost images provide cues that allow a per- added peripheral awareness is small Dr. Gottlieb emphasizes, son wearing Eli Peli’s prism glasses to avoid obstacles. and vision through the prism is even though the effect of At left, a man's the head and Feet become visible in blurred. We really don’t know how looking into the button the glasses. Only his arm would be visible otherwise. often they work.” prism may be disorient- Single sector prism: Another ing “for the first few minutes,” it is your eye doctor. Dr. Peli welcomes option is to mount a single prism on ultimately the double vision that inquiries from optometrists and oph- just one lens. This has a very differ- makes his system work. With train- thalmologists (see below). If you ent effect: When the wearer glances ing, he says, most patients who have would like to find out more about the sideways into the prism, it superim- used the system to date have benefit- Visual Field Awareness System, con- poses an image from the missing por- ed. He has also published research tact Dr. Gottlieb at his clinic. tion of the visual field onto the intact suggesting that some people who use vision. The result is diplopia, or the system may recover some of The next step “double vision.” The superimposed their lost visual field due to intact Dr. Peli and his colleagues at the image is supposed to provide a cue areas of the brain taking over the Schepens Eye Research Institute are for avoiding obstacles. function of the damaged area. gearing up for a study of how well Gottlieb “button ” prism: Daniel people wearing the prism glasses D. Gottlieb, OD, of the Gottlieb Vision Paying for it can drive a car. Presently some Group in Stone Mountain, Georgia, Another key difference in the two states test for visual field size and has developed a new type of single systems is price. Being fitted with the some don’t. In states that do test, sector prism called the Visual Field Gottlieb system-including installa- people with hemianopia’cannot Awareness System. It consists of a tion of the prism within the lens- drive--a major impediment to living small circular “button” prism mount- costs anywhere from $1,500 to independently. Also, Dr. Peli is evalu- ed off-center within one lens in a pair $3,000, depending on the prescrip ating whether other types of prism of eyeglasses. By scanning through tion (bifocals versus trifocals, for glasses can help people with retinal the prism, Dr. Gottlieb explains, instance) and various extra features. damage that turns their visual field patients build up a combined, or Then the patient is offered training in into a narrow tunnel-a common “gestalt,” view of their surroundings. how to use the system. Typically, a symptom of retinitis pigmentosa The button is optically clear, perma- dozen training sessions are required and glaucoma. @ nent, and easier to keep clean than for someone to become accustomed an off-the-shelf flat sector prism. Dr. to the system. This is followed by Gottlieb trains optometrists and oph- additional training sessions as need- thalmologists in how to fit people ed, “especially if they want to drive,” with the system and coach them in Dr. Gottlieb says. how to use it. It was available in at The cost of training can run an least 27 U.S. states and some foreign additional $1,200 to $1,500. Some countries. Dr. Gottlieb developed the people may have to travel out of system and holds the patent. state to reach eye doctors trained by Dr. Gottlieb, adding to the expense. Button prism vs Peli system Dr. Gottlieb says that most people When the person looks directly into with major medical insurance can get the button prism, it introduces reimbursed for the system. momentary double vision. At first, If you are interested in trying a this can be confusing to the patient, prism system, first discuss it with

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