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Margareta Claesson, John Armitage, Mats Lundström; Validation of Catquest-9SF – A Visual Disability Instrument for Corneal Transplantation. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1225.
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© ARVO (1962-2015); The Authors (2016-present)
To apply and validate a visual disability questionnaire, Catquest-9SF, using Rasch analysis, in order to optimize item fit to the construct, minimize test length and create a linear measure of visual disability in patients before and after corneal transplantation.
A group of patients (n=398) who were in the Swedish Cornea Registry, completed the Catquest -9SF questionnaire. 199 completed the questionnaire before their corneal transplant. The remaining patients (n=199), separate from the first group in order to maintain independence within the validation data set, submitted the questionnaire 2 years after their transplant. The Catquest-9SF contains 7 visual disability items and 2 global assessment items. The fit of these 9 items to a single construct was assessed with Rasch analysis using Winsteps 3.91.0 applied with an Andrich rating scale for each question type.
The existing response scale thresholds were ordered for all items. 68.5% of the variance was explained showing that the instrument measures a single underlying construct. The instrument distinguished well between different levels of participants’ ability (person separation 3.09, person reliability 0.91). All items fit the Rasch model expectation (infit and outfit mean squares between 0.7 and 1.3). Differential item functioning (DIF) showed that the level of response ability for only one item, satisfaction with vision, differed before and after surgery (1.08 logits). Finally, targeting showed that the item difficulty matched the level of the participants’ visual ability (<1 logit).
We have used Catquest-9SF, previously validated for cataract surgery, to quantify the visual disability of patients before and after corneal transplantation. The level of response ability of patients before and after transplantation differed only slightly for one item, satisfaction with vision. This is understandable given the poorer vision before transplantation. Catquest-9SF applied to corneal transplant patients therefore fits the Rasch model extremely well and can be used to assess change in visual disability after corneal transplantation.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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