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Susanne Gunda Pondorfer, Jan Henrik Terheyden, Robert Finger; Development of the Vision Impairment in Low Luminance (VILL) Questionnaire. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2658.
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To design and evaluate an instrument for assessing vision-related quality of life (VRQoL) appropriate for the specific visual impairment characteristic for early stages of age-related macular degeneration (AMD).
The questionnaire was developed in three steps with patients with early, intermediate and late AMD: (1) Based on in depth interviews (n=19) and two FGDs (n=5 each), content was developed followed by (2) questionnaire development using cognitive debriefing interviews (n=3) leading to a questionnaire version with 68 items with a five step response scale. (3) This version was then administered to 137 patients with early, intermediate and late AMD. Psychometric properties, such as response category functioning (floor and ceiling effect) and targeting of item difficulty to patient ability of the pilot Vison Impairment in Low Luminance (VILL) questionnaire were determined using Rasch analysis.
Following the Rasch analysis, several items were removed based on floor or ceiling effects, or misfit and a final pool of 37 items remained. The response scale was collapsed to four categories as one category was under-utilized. The targeting of the instrument was good with minimal difference in person and item means (0.52 logits). There was evidence of multidimensionality (eigenvalue of the first contrast = 5.95) in the scale, indicating that it may be reasonable to split the items into subsets including a functional and emotional wellbeing subscale
AMD patients report difficulty with vision-related activities and functioning under visually challenging conditions at all stages of the disease. These aspects were considered when developing the 37-item VILL which has demonstrated promising psychometric characteristics. Further assessments of reliability and validity are ongoing.
This is a 2020 ARVO Annual Meeting abstract.
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