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Stephen G. Whittaker, Ph.D.
William Feinbloom Low Vision Rehabilitation Service
Young Opportunities, Inc.
Pennsylvania College of Optometry
464 Sylvania Ave.
1200 W. Godfrey Ave
Glenside, PA 19038
Philadelphia, PA 19141
Telephone: (215) 572-5882
We will overview various assessment-tools and techniques that have enabled us to better plan a rehabilitation program and streamline the selection of assistive computer devices for people with visual impairment. Visual assessment tools have allowed us identify specific limitations and predict performance, reducing time consuming and frustrating trial-and-error. By using recordings of speech synthesizers that clients can take home, we significantly reduce the cost and time involved in evaluating speech systems as well. This presentation has been developed primarily for practitioners who are generally familiar with screen magnifiers and screen reader devices. We will elaborate on optical devices as an alternative to screen magnifiers and large monitors. A handout (available from S. Whittaker) will describe the procedures in detail and where to obtain products.
In the Feinbloom Center, the clientele nearly all have some visual function, and about 60% are elderly with adventitious vision loss. Our consumers and referring agencies require that we accurately estimate the time required for an assessment and the probable outcome before undertaking an assessment. We thus first perform a screening to estimate the time required for the computer assessment, the options that we will explore, and expected outcome. The actual computer assessment involves two stages.
In the first stage, we assess visual function, and determine the optimum visual setup for reading (magnification, lighting etc.). We then have clients read a passage under conditions that are as close as possible to these optimal conditions with optical devices, and screen magnification devices. Then they "read" similar passages by listening to computer-synthesized speech. The client finally decides if an optical device, screen magnifier and/or speech system is necessary. The second stage involves specific product assessment. We demonstrate only the products deemed necessary by the first stage under the previously determined, optimum, setup. To evaluate speech synthesizers, we send clients home with a recording of various speech synthesizers that we have developed.
These are the least expensive and easiest means to magnify a screen and work on any computer. One can achieve optical magnification by decreasing the working distance from the normal working distance of 40 cm to about 10 cm and then have an optometrist or ophthalmologist prescribe NVO spectacles. Unlike bifocals, NVO glasses are single lenses focused at one working distance. One must also prescribe a computer monitor stand with these devices to bring the monitor to the appropriate working distance while the user sits up straight. Relative-Mistance Magnification equals working distance before the change divided by the working distance after (for example, a decrease from 40 cm to 10 cm equals 4X magnification). One can experiment with these closer working distances in people younger than 30; however, older clients require near glasses to see clearly up close. To avoid eye strain and insure clearest vision, refer all clients to an optometrist or ophthalmologist for near evaluation if changing working distance. Specify the required working distance and recommendation for "NVO" in your letter of referral. Ask the optometrist or ophthalmologist to whom you refer where to obtain plus 2.5 to 10 diopter trial lenses to use with older clients and teach you how to use them.
For someone like a teacher, supervisor or repair person who must move from computer to computer, a telemicroscope is an ideal solution. With miniature telemicroscopes mounted on glasses people can achieve up to 6X magnification (more is possible but usually unacceptable). These allow a longer working distance but have a narrow field of view and are hard to hold steady. I recommend refer to an optometrist or ophthalmologist who specializes in low vision prescribe telemicroscopes.
If possible, we recommend a decrease in working distance as a lower cost alternative to magnifying a display with a larger monitor. Active Accessibility modifications and customizing colors and magnification within applications can be used very effectively in combination with an optical device for additional contrast and magnification. Active accessibility, however, as still too unreliable for a user to depend on. An optical device should provide sufficient magnification for someone to use a computer even when AA fails.
Screen magnifiers, like ZoomText Xtra or MAGic, magnify the display from 2X to 16X and enhance contrast and colors . To maximize the field of view on the monitor, , we consider relative-distance magnification with NVO glasses even when a user requires a screen magnifier. For example, by decreasing working-distance in half we can reduce screen magnification from 16X to 8X. Screen readers are programs like JAWS or WIN-Eyes that are used to read a computer display aloud with a speech synthesizer. With those with low vision we often recommend programs like ZoomText Xtra Level 2 that combine magnification and speech.
Jane is a 22 YO college student with bilateral aphakia and high myopia. She was a 3.0 GPA student prior to recent vision loss. Prognosis was uncertain. Like many of our older clients, at the time of the visit she was fearful of additional vision loss and felt overwhelmed. She had no prior computer skills and couldn't touch-type. Her distance Visual Acuity in the right eye was 20/100 and in left eye was light perception only. She was recently prescribed 10 diopters NVO reading spectacles
The M N Read is a single card (described in the handout) that enables one to quickly estimate the smallest and optimum print size for reading (in M units) and maximum visual reading rate. The M scale is a metric scale of print size, more standardized than the printer point scale. The M number indicates the distance in meters where a lower case n is barely seen by a someone with normal vision (retinal image size subtends an angle of 5 minutes).
First I determine the best test distance for reading. To do this I ask the client to wear the best reading glasses for computer use, if any. While looking at the largest print on the M N Read card, I move the card closer until it blurs and further until it blurs. Then I have the client select a preferred distance within this range of clear vision at keep in constant throughout testing. I then administer the M N Read (details in the handout)
In Jane's case she wore her 10 diopter NVO reading glasses. Her working distance was 10 cm. At this distance reading acuity was 0.6 M, optimum print size was 1.6 M, and maximum reading rate was 200 words per minute (wpm). Note than one must ALWAYS report working distance when reporting print size. For a computer evaluation, measure and record the optimum print size with a micrometer.
Reading rate greater than 150 wpm on the MNRead indicates that fluent reading is possible with magnification alone. For someone like Jane who has a visual reading aid like reading glasses or a CCTV, and is satisfied with the current level of reading comfort and speed, although I mention the speech option, I recommend evaluation of visual devices and screen magnification only. In Jane's case, she was not interested in speech.
I determine optimum magnification on a computer, I start with habitual NVO spectacles at the working distance set by the MNRead and on the computer display present M N Read length sentences (available from http://vision.psych.umn.edu/mnread.html). Using the micrometer, I adjust display magnification to the optimum print size predicted by the M N Read, time reading and repeat at higher and lower magnification, to the size that the user prefers. Jane was happy with 1.6M, (typical, unmagnified 12 point print on a 15 inch monitor). . She had no lighting complaints and reported acceptable reading speed and comfort with her NVO spectacles. Not suprisingly, Jane preferred normal color. She read a test paragraph at 156 wpm and reported good comfort.
Next I evaluated screen magnification. With her regular glasses I remeasured preferred working distance to 40 cm. This increased distance decreased relative-distance magnification to 1/4 of what it was at 10 cm. (10, the prior distance divided by 40, the new). To compensate, I magnified the display 4X from 2mm letters to 8--I ALWAYS use a micrometer rather than trust settings. For example, the 5X setting on the screen magnifier actually produced only 4X magnification. I controlled text scrolling while Jane read, and found a maximum rate of 145 wpm. I tried different magnification with no improvement. Having experienced reading with both assistive devices, Jane preferred her NVO glasses. I would have encouraged optical magnification because it is easier for a beginner to learn and a school to teach computer use without the added complexity of a screen magnifier. We planned to re-evaluate in a year.
45 YO English Teacher with diabetic retinopathy whose goals were to read student papers at 300 wpm, read new novels, type and proof own work, research Vatican Manuscripts, and read handwritten exams.
Letter acuity was 20/40 in his better eye. Reading acuity was 2.0M at 40 cm. Optimum print size was 4.0M at 40 cm. Maximum reading rate was a slow, halting 50 wpm. He had rejected NVO glasses for reading, preferring a CCTV. He reported lighting was critical for best vision. I concluded that a 4 hour comprehensive visual assessment was required to identify what was limiting his reading rate and that he probably would need speech. With combined visual and speech he should be able to achieve all his goals except reading handwritten exams.
Usually clients with 20/40 acuity, respond well to simple optical magnification but Mr. K. did not. Something other than reduced acuity was limiting his performance. I performed an analytical assessment; the details of each procedure are in a handout.
Letter contrast sensitivity charts, are letters of the same size that decrease in contrast. The client reads down the chart until reaching the lowest contrast letters that can be read. The contrast of these letters is contrast threshold, expressed as a percentage from 0 (no contrast) to 100%. Normal contrast threshold is below 2%. With contrast threshold between 5% and 10%, a moderate loss; one can compensate by adjusting lighting, eliminating glare, and enhancing print or computer display contrast. Above 10%, a severe loss, will limit visual reading even under optimal visual conditions. If contrast threshold is worse than 5% (or if the client reports that proper lighting is critical), one must eliminate glare, screen reflections, optimize lighting and explore contrast enhancement options . Mr. K.'s best contrast threshold was 13%, a severe loss.
Mr. K also had a reduced visual field. The visual field is an area of vision expressed as degrees. For example, Mr. K. had a visual field reduced to about 20 degrees horizontally by 10 degrees vertically, twice the size of a fist at arm's length. A scotoma is a blind area or area of reduced vision within a visual field. Mr. K had patches of reduced vision or relative scotoma within his visual field. People with reduced visual fields can still scan a larger area by moving their eyes, but tend to miss objects that appear unpredictably outside the field or within a scotoma. People with severely reduced visual fields like advanced retinitus pigmentosa or glaucoma also do not respond well to magnification because magnification reduces the number of letters they can see at a time.
Having performed these tests, I concluded that Mr. K's reading was limited by severe reduction in contrast sensitivity and relative scotma. I didn't bother evaluating reading with NVO glasses, and went directly to computer display with optimal magnification and contrast. In this case, I took considerable care to eliminate glare, and optimize lighting. He read fastest with reverse high contrast. Still he only read only 45 wpm and required larger print than predicted by the MNRead
Like many with recent vision loss, Mr. K resisted the idea of depending on speech to read. I have developed a cassette tape that helps people overcome this resistance. Paragraphs are read at increasing speeds from about 150 to 400 wpm by DECTalk. The fastest reading speed that someone can still understand, is their "listening rate". I do this test right after they read visually and report the difference in reading rate. Mr. K's listening rate was 400 wpm. Having experienced the difference in speed and comfort between visual reading and listening, he was sold on speech. This opened up the possibility of a screen reader with a speech synthesizer and a document readeras well as a screen magnifier.
We must be clear on our objectives in using adaptive technology. Comfort, speed and competitiveness are clearly goals, but the clarity of these goals gives way to the psychological resistance to admitting the need for adaptive technology to achieve them.
Even when it is clear that the person could work faster with the use of speech this resistance may express itself in a preference for screen magnification which is slower. The best one can hope for in an evaluative session is to assure that the person understands the differences in speed and comfort that can be obtained.
To evaluate speech, we begin with a description of the function of the screen reader and the speech synthesizer, then go on to explain that the choice of a speech synthesizer is dependent on ones listening comfort, and that the choice of the screen reader can be dependent on the programs used, the operating system and networking required, and the tasks performed with these programs.
In the past evaluating speech synthesizers has been an especially time-consuming and expensive service. Since many do not have the facility to get to a site where they can evaluate various speech synthesizers, we have developed a CD-ROM disk which enables an evaluation of over 15 speech synthesizers (internal, external, software, notetakers) on a computer with a sound card. Using straightforward speech-friendly menu selection software, the user can select synthesizers. The software also makes it very easy for an evaluator to make a demonstration cassette tape from the CD for selected synthesizers. The CD also includes a general introduction to screen readers and speech synthesizers as well as a detailed description of each synthesizers including its responsiveness. Prior to a product evaluation, we send a cassette tape to users with the general introduction and demonstration of just the available speech synthesizers asking the clients to select their favorite. We use the computer to demonstrate the synthesizers in our center.
To give a user time to become accustomed to each synthesizers, we chose Lincoln's Gettysburg Address as it is contextually complete and allowed for a thorough listening experience. We also had the synthesizer read 4 sentences comprising several words that do not lend themselves well to phonetic English pronunciation rules. Then, to assure that the person had the opportunity to assess the synthesizer at different speeds we played these short sentences at four difference speaking speeds. This has significantly decreased assessment time and the cost of setting up a demonstration.
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