Integrating Adaptive Technology in Your Evaluation
By: Stanley Woo OD, MS, FAAO
Low vision patients, young and old, are increasingly savvy with technology. Gone are the days when it was too costly for kids and too complicated for older folks. The explosion of information on the Internet has thus made it integral for the primary care provider of low vision rehabilitation to have access to video magnifier systems (VMS).
In our practice, we utilize the VMS as part of our examination procedure for every patient with an interest in reading regardless of visual acuity. First, it provides diagnostic information regarding the patient’s optimal magnification. Second, it permits the patient to utilize the latest adaptive technology and recognize the potential ease with which it may meet their reading goals, whether now or at some future date. Lastly, it assures that patient that their low vision evaluation encompasses the gamut of adaptive devices that may be of benefit to them rather than leaving them to wonder why “Aunt Edna uses a reading machine but my doctor never mentioned it.”
From a diagnostic standpoint, we use a VMS to provide the following information: preferred working distance from the print/screen, contrast and polarity (black on white, white on black, color combination, etc.), and enlargement ratio. One of the principal advantages of the VMS is that the patient may sit at a more comfortable distance from the screen displaying their reading material. Given the choice between using a 5x microscope at 5 cm from their eye or sitting 50 cm from a monitor, it’s not hard to imagine which might be the more comfortable option. Next, regardless of acuity, there are a number of conditions that benefit from the increased contrast with VMS. A quick cycle through the options yields information that may relate to glare and filters to address related complaints. Lastly, the degree of magnification or enlargement that the patient finds most comfortable on the VMS can often provide valuable insight into the final prescription and highlight the need for acuity reserve for comfortable reading.
A patient with 20/200 vision with age-related macular degeneration is able to read 2M print at 20 cm. This corresponds to slightly larger than the large print Reader’s Digest. As a Boomer, they're interested in being able to track their retirement portfolio and would like to read the stock market tables, which we assume to be about 0.5M print. To read this print, they would have to hold the stock table at about 5 cm with the appropriate correction, which might include a +20D lens (5x magnifier). However, using the VMS, we determine that they're most comfortable sitting 50 cm from the screen, which is the same situation they have for their computer. With white print on a black screen (reverse polarity) they appreciate the high contrast without an excess amount of light or glare. The improvement is especially noticeable when compared to the regular newspaper.
To identify the optimal magnification, the patient brackets about an enlargement ratio that provides the optimal balance between legibility and field of view. The greater the magnification the easier it is to read but the fewer the number of words that are visible on the screen at one time. Ideally, they should find a happy middle ground and slide the material on the X-Y table to access print across the line. In this case, our patient enlarges the stock table size a factor of 12 on the screen, thus creating the equivalent of holding the stock table at 50cm/12 or 4.2 cm away from their eye.
The diagnostic information that we glean includes the important of contrast to maximize the legibility of the print, and a desire for a slightly increased acuity reserve because of the increased magnification. With an equivalent viewing distance of 4.2 cm, the patient is indicating that they prefer around +24D or a 6x magnifier. Thus, we may consider a stand magnifier system, hand-held, or microscope for comparison with the VMS.
The time taken to integrate the use of a VMS is minimal, and yet it provides a number of significant advantages. Your practice has the latest technology in LVR, diagnostic information that can impact prescriptive decision making is gained, and the importance of contrast and glare may lead to further testing and evaluation of filters. Ultimately, the perception of the patient about the range of options is improved, thus enabling them to make a more informed decision under your expert guidance.