Development and validation of a vision-specific quality-of-life questionnaire for Timor-Leste.

PURPOSE To develop and determine the reliability and validity of a vision-specific quality-of-life instrument (TL-VSQOL) designed to assess the impact of distance and near vision impairment in adults living in Timor-Leste. METHODS A vision-specific quality-of-life questionnaire was developed, piloted, and administered to 704 Timorese aged >or=40 years during a population-based eye health rapid assessment. Rasch analysis was performed on the data of 457 participants with presenting near vision worse than N8 (78.5%) and/or distance vision worse than 6/18 (69.8%). Unidimensionality, item fit to the model, response category performance, differential item functioning, and targeting of items to participants were assessed. RESULTS Initially, the questionnaire lacked fit to the Rasch model. Removal of two items concerning emotional well-being resulted in a fit of the data (overall item-trait interaction: chi(2) (df) = 81 (51); mean (SD) person and item fit residual values: -0.30 (1.02) and -0.32 (1.46), and good targeting of person ability and item difficulty was evident. Poorer distance and near visual acuities were significantly associated with worse quality-of-life scores (P < 0.001). Person separation reliability was substantial (0.93), indicating that the instrument can discriminate between groups with normal and impaired vision. All 17 items were free of differential item functioning, and there was no evidence of multidimensionality. CONCLUSIONS This 17-item TL-VSQOL has high reliability, construct, and criterion validity and effective targeting. It can effectively assess the impact on quality of life of adult Timorese with distance and near vision impairment. The TL-VSQOL could be adapted for use in other low-resource settings.