A case-comparison of intermittent exotropia and quality of life measurements

A Vision Quality of Life Questionnaire that combines the SF-20 and a Vision Quality Scale developed by the authors was pilot tested in a case-comparison of extreme groups, patients with intermittent exotropia (IXT) and those with no vision problems (Non-IXT), at the University of Houston (UH) Optometry Clinic. The purposes of the study were to measure the internal consistency reliability and examine the validity-related evidence of vision function associated with the instrument. The pilot study involved mailing the instrument to 52 patients in each group (IXT and Non-IXT patients). IXT patients were then frequency-matched by age and separately by sex, to control for confounding variables, to Non-IXT group patients. The Cronbach's Alpha internal consistency reliability of both scales was acceptable at > 0.70 for both the IXT and Non-IXT groups. The Wilcoxon signed ranks test was used to determine validity-related evidence. The differences between groups on the SF-20 (p = 0.0276) and Vision Function Scale (VFS) (p = 0.0385) confirm that the scales discriminate between IXT and Non-IXT populations. Two conclusions can be drawn from the pretesting and pilot testing of the SF-20 and the VFS: (1) both have acceptable internal consistency reliability scores, and (2) both show validity-related evidence that they can discriminate vision function between IXT and Non-IXT patient populations.