Objectives: To assess the test-retest reliability and responsiveness of the VF-14, which is an index of functional impairment in patient with cataracts.
Design: Observational longitudinal study. Patients were enrolled prior to undergoing their first cataract surgery between July 15 and December 15, 1991, and they were followed up for 1 year after surgery.
Setting: Patients were recruited from 72 ophthalmologists' practices in three US cities.
Patients: Five hundred fifty-two patients who had undergone a surgical procedure in only one eye by the 4-month postoperative follow-up (responsiveness analyses) and a subset of these (n = 426) who had not subsequently undergone surgery for the second eye by the 12-month postoperative follow-up (reproducibility analyses).
Main outcome measures: Two health status measures (the VF-14 and the Sickness Impact Profile, two global measures of a patient's trouble and satisfaction with his or her vision, and best corrected visual acuity in each eye.
Results: The VF-14 is highly reproducible, with an intraclass correlation coefficient of .79 when patient-rated criteria are used to define stable patients. The intraclass correlation coefficient was lower (.57 to .71) when various measures of visual acuity were used to define stable patients. The VF-14 is also about three times more responsive to a change in vision than the Sickness Impact Profile, which is a generic health status measure (effect size of approximately 1.00 vs 0.30). Estimates of the responsiveness of the VF-14 and the Sickness Impact Profile were not associated with preoperative visual acuity in the operated on or better eye. Responsiveness of the VF-14, however, was higher in patients with greater self-rated trouble with vision preoperatively.
Conclusions: The VF-14 was reproducible in stable patients during an 8-month period, and it was more responsive to clinically significant changes in vision than was a generic health status measure (ie, the Sickness Impact Profile).