Abstract
PURPOSE: To develop and validate a novel patient-reported outcome (PRO) measure to assess vision-related functioning in individuals with severe peripheral field loss (PFL). DESIGN: Prospective outcome measure development/validation study. METHODS: A 127-item questionnaire was developed based on a prior qualitative interview study. A total of 116 participants with severe PFL due to retinitis pigmentosa (RP) or glaucoma were recruited at the Kellogg Eye Center and completed the Likert-scaled telephone-administered questionnaire. Included participants had a horizontal extent of their visual field <20 degrees (RP) or a mixed or generalized stage 4 to 5 defect using the Enhanced Glaucoma Staging System (glaucoma) in the better seeing eye (or in 1 eye if the fellow eye visual acuity was <20/200). Response data were analyzed using exploratory factor analysis and Rasch modeling. Poorly functioning items were eliminated, confirmatory factor analysis was used to ensure scale unidimensionality, and the model was refit to produce the final instrument. RESULTS: The final Low Vision Severely Constricted Peripheral Eyesight (LV-SCOPE) Questionnaire contains 53 items across 6 domains: mobility, object localization, object recognition, reading, social functioning, and technology. There were 74 items removed because of high missingness, poor factor loadings, low internal consistency, high local dependency, low item information, item redundancy, or differential item functioning. Using Rasch item calibrations, person ability scores could be calculated for each of the 6 unidimensional LV-SCOPE domains with good test-retest stability. CONCLUSIONS: The LV-SCOPE Questionnaire provides a valid and reliable measure of vision-related functioning across 6 key domains relevant to individuals with severe PFL. Findings support the clinical utility of this psychometrically valid instrument.