Purpose: There is increased recognition that a rigorous approach to functional assessment should complement the assessment of clinical status. The authors compare the reliability, validity, and responsiveness to clinical change of a visual function index (VF-14) in non-U.S. and in U.S. patients with cataracts.
Design: An observational longitudinal study was performed.
Participants: One thousand four hundred seven first eye cataract surgery patients were recruited in four international sites: Manitoba (Canada), Denmark, Barcelona (Spain), and the United States.
Intervention: Patients were evaluated before cataract surgery and at a 4-month postoperative follow-up visit. Patients completed the preoperative interview and the clinical examination (766 in the United States, 152 in Manitoba, 291 in Denmark, and 198 in Barcelona), and 91.3% of those (1284) also completed the 4-month postoperative follow-up interview and were evaluated postoperatively by an ophthalmologist.
Main outcome measures: The authors used the following measures: the visual function index (VF-14), the Sickness Impact Profile (SIP), global measures of patients' trouble and satisfaction with vision, and best-corrected visual acuity (VA) in each eye.
Results: The VF-14 showed a high internal consistency reliability level in all sites (Cronbach's alpha coefficients > or = 0.84). Correlation of preoperative visual function index scores with the Vision-Related SIP was strong (r = -0.68 in non-U.S. and r = -0.57 in U.S. patients) and with VA in the eye with better vision was moderate (r = 0.40 and r = 0.27, respectively), the pattern of relationships being very similar among U.S. and non-U.S. patients. In patients with only first-eye surgery who reported that their initial trouble with vision had improved, the amount of change in visual function as assessed by the VF-14 (effect size) was large (1.01 for the non-U.S. patients and 1.17 for the U.S. patients).
Conclusions: The non-U.S. versions of the visual function index (VF-14) analyzed are as reliable, valid, and responsive to clinical change as the original U.S. version. These versions are appropriate for international studies of cataract patients outcomes and possibly in routine clinical practice.