What Are Assistive Technologies?
Assistive technologies are tools that help people who are partially sighted or blind be more independent at work, in school and at home. These tools, which can be sophisticated or surprisingly simple, are designed to make it easier to access printed material, to use computers, to travel and to perform activities of daily living.
Assistive technology incorporates high tech methods. Some examples of assistive technology include:
Video magnification systems like closed circuit televisions (CCTVs) and portable video magnification devices,
Computer hardware and software that provides screen magnification, synthesized speech, tactile display, or combinations of these,
Other assistive devices for daily living, like talking scales, talking glucometers, color identifiers, talking compasses, and a variety of other devices.
Low vision devices, such as microscopic spectacles, magnifiers and telescopes, utilize optical magnification to help visually impaired users achieve their goals. These optical low vision devices are still the staple of low vision care and have certain advantages in comparison to assistive technology. They are often more portable and more affordable than assistive technology devices and can be used in a variety of situations. For some patients, optical devices may just be easier to use. These devices can also have certain limitations, however, especially in higher powers, including a reduction in field of view, working distance, light and contrast. These limiting factors can sometimes significantly impact a person's successful use of optical low vision devices. When optical devices are difficult to use, assistive technology may allow the person to function more effectively.
Evaluating Who Can Benefit
For the person with partial sight, the first step is to have a low vision evaluation. During this visit, the low vision doctor will take a detailed history and ask questions about the individual's functional problems. The doctor will also investigate any physical limitations the person may have, which might interfere with the use of certain types of devices. Then, the low vision clinician will administer a series of tests to evaluate the patient's visual function, including visual acuity, visual fields (central and peripheral), contrast sensitivity and color vision. The information the doctor obtains from this testing will provide clues about whether assistive technology may be beneficial and, if so, what types of technology to prescribe.
Visual Function and Its Impact on What a Doctor Prescribes
Visual Acuity Loss: For the person with very reduced acuity, assistive technology may be easier to work with than optical magnification. Devices like CCTVs can offer not only higher but also variable magnification. They can also allow the person to function more comfortably by providing increased working distance from the task at hand.
Other types of assistive technology feature speech support, which may better suit an individual with very reduced acuity. If the person cannot see the word, the device can read it out loud. Some patients may also function better binocularly. Yet, if a person's visual acuity is worse than 20/200, binocularity becomes difficult with an optical device. Maintaining binocularity is possible at high levels of magnification through assistive technology.
Central Field Loss: Patients with central scotomas often have to use eccentric viewing to function more effectively. When a person has a large scotoma, being able to effectively use an eccentric point can be more difficult with optical magnification. Eccentric viewing may be easier with an assistive technology device.
Additionally, as fixation moves further from the fovea, the impact of crowding increases. Using different types of text presentation can lessen the effects of visual crowding. For example, studies have reported that using text stretching to increase the spacing between letters and words can reduce crowding and may be beneficial for the person trying to read with a central scotoma. Presenting text in a scrolled fashion (like the marquees at the bottom of the screen on television news programs), or presenting words one at a time consecutively in the same place in the person's field, may also make reading with an eccentric point easier. This type of text manipulation is possible via assistive technology.
Peripheral Field Loss: Patients with severely constricted fields may not respond well to optical magnification since the print or object being magnified may stretch into their field loss. These same patients may also have difficulty with optical devices because they may have problems controlling the position of their usable field at near distance, which can be especially true when using high plus spectacles.
Since visual field is an angular measure, a person's linear field of view increases further from the eye. Therefore, if you can present higher magnification at a greater distance, it may help someone with a severely constricted field see more. Assistive technology can accomplish this.
Contrast Loss: Optical devices themselves can reduce light and contrast, so a patient with reduced contrast sensitivity may have greater difficulty using a magnifier or other low vision optical device compared to someone who doesn't experience reduced contrast sensitivity. Additionally, patients with reduced contrast may require higher magnification than would be indicated by their acuity alone, but stronger-power optical magnifiers and microscopic spectacles are more difficult to use. A patient with severe contrast sensitivity loss may function better using reverse contrast, which can only be achieved with electronic magnification assistive technology.
Color Vision Loss: Many eye diseases, including macular degeneration, diabetic retinopathy, glaucoma and optic atrophy, can lead to reduced color perception. When color perception is impacted, a person may have difficulty with color contrasts, which may make text or objects on a colored background more difficult to see. Using electronic magnification, colors can be converted to black and white, and if necessary, contrast can also be enhanced. In addition, if a person has problems with color identification, assistive technology can offer solutions.
Other Considerations: A patient's needs and goals are a primary consideration in determining whether assistive technology will be beneficial and in deciding which kind of technology would be most appropriate. For certain tasks, such as reading prices at the store, for example, it makes more sense for most patients to use a simple magnifier in a strength and design appropriate to their capabilities rather than turning to assistive technology.
What about a person's age? While there is no question that visual needs are age dependent, age alone should not be a factor when considering if assistive technology is appropriate. People of all ages can benefit from assistive technology. However, a patient's abilities can become a factor. As with any activity, a physical disability or an impaired ability to learn to use a device may prohibit using assistive technology.
Types of Assistive Technology
In every facet of our lives, technology is advancing at a very rapid pace. This is equally true in the area of vision rehabilitation. What follows is a brief overview of available assistive technologies.
Current video magnification systems include:
Desktop CCTVs (see photo 1) with enhanced features (auto focus, speech commands, flat screens, text manipulation),
Handheld cameras (see photo 2) that interface with a standard TV set or other portable devices, such as head borne video displays or miniature flat panel displays,
Head mounted systems (see photo 3), where the camera and LCD displays are combined in a single unit,
Self contained portable units (see photo 4), where the camera and screen are in single unit (these now include miniature LCD magnifiers (see photo 5) that are very small and lightweight).
Computer based systems, which allow users to access information using screen magnification, speech output, or both, are also popular. Computers can be used in conjunction with scanners to allow users to import typewritten material, which they can then access using speech or screen enlargement. For those people who are not computer users, standalone systems can convert typewritten text to speech and read documents aloud in a synthesized voice.
An ever-increasing number of "simple" technologic devices that provide greater accessibility for those with vision impairments have been appearing on the market, such as personal digital assistants (PDAs) using speech recognition to cell phones with talking alerts. Technology continues to improve, and in many cases, has also become less expensive. Ultimately, all of our patients will benefit from assistive technology in the future.
Michael Fischer, OD, FAAO