Development of Improved Visual Field Testing as an Outcome Measure for Treatment Trials in Usher Syndrome (funded January 2007)
Usher syndrome is a genetic condition causing both hearing loss and vision loss, and is the most common cause of deafblindness in the Western world. Some individuals with Usher syndrome have moderate hearing loss, where others are born totally deaf. With the advent and increasing availability of the cochlear implant, the hearing loss in Usher syndrome can be managed and even, in many cases, cured. The vision loss in Usher syndrome, however, results from retinitis pigmentosa (RP), a progressive disorder of the retina for which there is no known cure or effective treatment. The progressive vision loss resulting from RP is therefore the most disabling aspect of this condition. Finding and delivering effective treatment for RP is the urgent mission of our research.
Accurate monitoring of retinal function in retinitis pigmentosa requires the use of several test methods, including assessment of the visual field and the electroretinogram (ERG). The visual field test quantifies visual field loss, while the ERG measures the electrical impulses of the retina to quantify retinal cell function. Over the last 30 years, the Oregon Retinal Degeneration Center (ORDC), under the direction of Dr. Richard Weleber, has become one of the premier centers in the world for the measurement and standardization of retinal function in RP. As a direct result of Dr. Weleber’s passion and expertise, the ERG has evolved into a highly accurate, sensitive, and reproducible test method. The visual field, however, while extremely informative, has a high degree of test-retest variability. This variability decreases the utility of the visual field test in clinical treatment trials, where accurate, sensitive, and reproducible test measures are vital for monitoring treatment effectiveness. In fact, the lack of acceptable visual field testing for retinal dysfunction is now a limiting factor in initiating clinical trials for RP and Usher syndrome. Dr. Weleber has joined with Dr. Chris Johnson, an internationally known visual field expert with over 20 years of experience in glaucoma research and test development, to refine and develop visual field testing techniques specific to field loss in RP.
This study will assess and optimize computerized visual field test methods for patients with RP by addressing the following three specific aims: to ascertain the test-retest variability of visual field measurements in RP, to spatially characterize visual field losses specific to particular subtypes of RP (including Usher syndrome), and to develop novel testing algorithms that will enable us to move forward with clinical treatment trials. At the conclusion of this study, we will publish our results and make recommendations to the scientific community regarding the best test strategy to use in multi-center clinical treatment trials.