Two new computerized tests increase the ability to measure remaining vision in patients with retinitis pigmentosa (RP) and other blinding diseases, reports a study in the October issue of Optometry Vision Science, official journal of the American Academy of Optometry. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.
The new tests can assess visual acuity below the limit of detection of standard tests—and may play an important role in evaluating new treatments for severe vision loss, such as artificial retinas. The study was performed by Ava K. Bittner, O.D., Ph.D., of Johns Hopkins University, Baltimore.
Two Computerized Tests Are Reliable for Evaluating Remaining Vision
Current tests for evaluating vision in patients with blinding diseases have limited ability to detect very low levels of remaining vision. Beyond a certain point, vision professionals must rely on simple, subjective tests—such as counting fingers or detecting hand motion—to get a rough estimate of the patient's remaining vision.
The new computer-driven tests—the Grating Acuity Test (GAT) and Grating Contrast Sensitivity (GCS) test—evaluate patients' ability to see the direction and contrast in a black-and-white, or gray and white striped ("grated") pattern. In these tests, patients are presented with grated patterns on a high-definition liquid crystal display screen. Patients indicate the direction of the stripes by pushing buttons that are identifiable by touch.
The GAT and GCS tests were evaluated in a sample of 20 legally blind patients with RP (a genetic disease causing destruction of the retina) or other retinal diseases. The goal was to determine whether the new tests would be useful in measuring remaining vision in patients with these blinding diseases, compared to current letter tests for assessing low vision.
The GAT and GCS tests showed good reliability, with consistent results on repeated testing. The new tests were also able to detect lower levels of remaining vision, compared to standard tests. Because the grated patterns are more easily recognized than letters, the visual acuities measured by the new tests tended to be higher than those measured by the conventional tests.
The new tests were able to detect visual acuities as low as 20/4000, compared to 20/1600 with current low-vision letter tests. (A person with 20/4000 vision would need to be 20 feet away to read letters that a person with normal vision could read from 4,000 feet away.) Because the GAT and GCS tests were computerized, the results were easily quantified and not as subjective as perceiving hand motion.
The GAT and GCS tests were developed for use in clinical trials of the Artificial Silicon Retina—a computer chip implant that has shown some promise in restoring useful vision in patients with severe vision loss due to RP. Several potential treatments for blinding retinal diseases are under development. Because of their possible risks, these treatments are likely to be tested first in patients who have little remaining vision to lose.
The new tests provide a promising new approach to testing vision in such patients—and, the researchers hope, demonstrating gains in vision in response to new treatments. Dr. Bittner and colleagues conclude, "Computer-driven grating tests appear to be reliable, capable of evaluating vision that may fall outside of the range of standard clinical tests and may be useful during clinical trials for advanced eye disease."
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