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Sarah McCague, Jennifer Wellman, Fan-Fan Yu, Satha Thill, Julie DiStefano-Pappas, Jean Bennett, Dominique Cross, Kathleen Marshall, Katherine High, Daniel C Chung; Mobility testing validation study - Using a novel, standardized mobility test to evaluate functional vision in patients with inherited retinal degeneration. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4774.
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© ARVO (1962-2015); The Authors (2016-present)
Currently, several therapies for low vision due to inherited retinal dystrophies are under investigation. Therefore, there is a growing need for validated endpoints to measure functional vision in these populations. This study examined the use of a novel standardized mobility test (MT) as a measure of functional vision in normal sighted individuals and in those with inherited retinal degeneration. We evaluated the construct and content validity, reliability, and the ability of MT to detect changes in functional vision over time.
28 low vision subjects (all with an inherited retinal degeneration) and 26 normal-sighted controls, age 4 through 39 years, were followed for three visits over one year. At each visit subjects completed MT, standard visual acuity and visual field tests, as well as a patient questionnaire. Twelve unique MT course configurations, each with the same number of turns and obstacles, were developed and selected randomly to minimize learning effect. Subjects were evaluated for accuracy and speed on MT at 9 standardized light levels between 1 lux and 400 lux. Tests were scored at an independent reading center by at least 2 trained graders and subjects were assigned a final score of “pass” if they succeeded in both accuracy and time assessments.
Our MT clearly distinguishes those with normal vision from those with low vision. All control subjects passed all MT attempts at all visits and all light levels, whereas low vision subjects showed a wide range of performance. Inter and intra-grader variability assessments show strong agreement. Additionally, course layout variability assessments indicate both time and accuracy are comparable across courses. Compared to standard measures of vision, subjects with visual acuity loss greater than 0.5 LogMAR appear to have significantly worse MT accuracy. A similar cut-off effect can be seen with visual fields.
Our MT shows both construct and content validity in differentiating low vision from control populations and identifying a range of performance in low vision patients. MT can also demonstrate the changes in functional vision over time. Course assessment has shown that all 12 courses are of equal difficulty. QA grading activities show high reproducibility of results and reliability of this endpoint.
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