Rasch Validation of the VF-14 Scale of Vision-Specific Functioning in Greek Patients.

The Visual Functioning-14 (VF-14) scale is the most widely employed index of vision-related functional impairment and serves as a patient-reported outcome measure in vision-specific quality of life. The purpose of this study is to rigorously examine and validate the VF-14 scale on a Greek population of ophthalmic patients employing Rasch measurement techniques. Two cohorts of patients were sampled in two waves. The first cohort included 150 cataract patients and the second 150 patients with other ophthalmic diseases. The patients were sampled first while pending surgical or other corrective therapy and two months after receiving therapy. The original 14-item VF-14 demonstrated poor measurement precision and disordered response category thresholds. A revised eight-item version, the VF-8G ('G' for 'Greek'), was tested and confirmed for validity in the cataract research population. No differential functioning was reported for gender, age, and underlying disorder. Improvement in the revised scale correlated with improvement in the mental and physical component of the general health scale SF-36. In conclusion, our findings support the use of the revised form of the VF-14 for assessment of vision-specific functioning and quality of life improvement in populations with cataracts and other visual diseases than cataracts, a result that has not been statistically confirmed previously.