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Developing an instrumental activities of daily living tool as part of the low vision assessment of daily activities protocol.

PURPOSE
To determine the validity, reliability, and measurement characteristics using factor and Rasch analysis of the Very Low Vision Instrumental Activities of Daily Living (IADL-VLV) in persons with severe vision loss.


METHODS
From an initial pool of 296 tasks, 25 were shortlisted after conducting a Delphi survey with persons designated legally blind. Using further input from occupational therapy and low-vision professionals, 11 activities were chosen to be pilot tested. Forty legally blind participants (better eye visual acuity < 20/200) underwent clinical assessments and functional tests as well as the 53 IADL tasks related to the 11 activities. The task pool was refined and condensed using factor and Rasch analysis.


RESULTS
Based on iterative principal component analyses, tasks were grouped together into the following domains: reading signs/information access, signature placement, clothes sorting, shelf search, gesture recognition, clock reading, and table search. A final selection of 23 tasks yielded satisfactory measurement characteristics, differentiated between at least four different levels of IADL performance (person separation of 3.8), and had adequate task difficulty for the tested sample (person mean -0.61). In multivariate analyses, only visual acuity (VA) and percent of remaining visual field (VF) were associated with IADL performance.


CONCLUSIONS
Using a large item pool, participant, and expert input, as well as factor and Rasch analysis, we designed a valid and reliable assessment to measure vision-related IADL performance in persons with severe vision loss. This assessment tool can be used in clinical sight restoration trials.