Variability in Perimetry Study (VIP II)
Improved Assessment of Visual Field Change is a trial aimed at investigating mechanisms of visual field testing variability. We have found using larger stimulus size substantially lowers short-term variability. In this study, we will determine if larger stimuli detect visual field change at an earlier time. We are also developing a statistical model that accounts for correlations of neighboring test locations.
|Study Design:||Observational Model: Case Control
Time Perspective: Prospective
|Official Title:||Improved Assessment of Visual Field Change|
- time to significant visual field change [ Time Frame: 4 years ] [ Designated as safety issue: No ]
|Study Start Date:||July 2010|
|Estimated Study Completion Date:||June 2014|
|Estimated Primary Completion Date:||June 2014 (Final data collection date for primary outcome measure)|
Disease of the optic nerve, including glaucoma, is the leading cause of blindness in the United States. Treatment decisions for optic nerve diseases are based largely on the changes in visual function that occur mostly as a consequence of disease progression. Unfortunately, the decision as to whether change of visual function has occurred is often difficult because of the high retest variability of conventional visual field testing (perimetry). This variability is so high that with moderate visual loss, a minimum of six tests are often needed in patients with optic nerve damage to reliably distinguish visual field deterioration from random variation. Our preliminary data show that a substantial portion of the variability of perimetry lies in the type of stimulus used and the testing strategy applied.
OBJECTIVES: We propose to test the hypothesis that a large portion of total perimetric variability in patients with visual loss is due to a poor signal-to-noise ratio associated with using a small fixed-size stimulus.
RESEARCH PLAN AND METHODS: To test this hypothesis, we are examining patients with optic nerve diseases with conventional automated perimetry (size III) and tests having large-sized and scaled stimuli (size V, size VI (custom perimeter) and luminance size threshold perimetry - a test where threshold is found by changing stimulus size rather than stimulus intensity). Over four years we will test 100 patients with and glaucoma and 60 normals each eight times. In addition, we are retesting 50 subjects once a week for 5 weeks. We are also studying the associated structural-functional correlations using OCT and developing a statistical model that accounts for correlations of neighboring test locations.
Perimetric variability and the reliable identification of visual field change is the single most difficult problem in visual testing today. We anticipate identifying a method that allows efficient and accurate determination of visual field change. Identification of a superior method would (1) reduce the number of examinations needed, thereby reducing the costs of medical care; (2) minimize misdiagnosis, unnecessary testing and even unnecessary surgery that results from mistakenly interpreting fluctuation of the visual field as progression or improvement; (3) allow earlier disease intervention and (4) reduce the costs of clinical trials.
|United States, Iowa|
|VA Medical Center, Iowa City|
|Iowa City, Iowa, United States, 52246-2208|
|Principal Investigator:||Michael Wall, MD||VA Medical Center, Iowa City|