Measuring outcomes of cataract surgery using the Visual Function Index-14.
OBJECTIVE
To determine which version of the Visual Function Index-14 (VF-14) most precisely measured cataract surgery outcomes, rescale the VF-14 using Rasch analysis, and create a short-form version for comparison.


METHODS
Flinders Medical Centre, Adelaide, South Australia, Australia.


METHODS
In this cohort study incorporating questionnaire development, participants were drawn from the cataract surgery waiting list at Flinders Medical Centre. There were 2 cohorts: a preoperative cohort used for questionnaire development and an outcomes cohort. All patients had cataract surgery by phacoemulsification with intraocular lens implantation. Rasch analysis was used to refine the VF-14 into valid long-form (VF-11R) and short-form (VF-8R) versions. The ability of 8 versions (original; 2 proposed versions; 5 previously proposed versions) of the VF-14 to discriminate cataract surgery outcomes was compared with that of the standard VF-14 using the relative precision method.


RESULTS
The preoperative cohort comprised 210 patients and the outcomes cohort, 51 patients. Large gains in visual functioning occurred with cataract surgery, and these were detectable with all versions of the VF-14. The largest gain in precision, 125% (relative precision. 2.25), occurred for VF-8R. Short forms that were not Rasch scaled showed gains in precision, from 23% to 80%. The VF-8R also showed the largest gains in precision in 2 subgroups: with ocular comorbidity (relative precision, 2.14) and without ocular comorbidity (relative precision, 2.48).


CONCLUSIONS
Results show an unequivocal advantage to using Rasch-scaled scores for assessing cataract surgery outcomes. The 8-item, Rasch-scaled VF-8R appears ideally suited for measuring cataract surgery outcomes given its high precision and short test time.


BACKGROUND
No author has a financial or proprietary interest in any material or method mentioned.
Gothwal
Vijaya K
VK
NH&MRC Centre for Clinical Eye Research, Department of Optometry and Vision Science, Flinders Medical Centre and Flinders University of South Australia, Bedford Park, South Australia.
Wright
Thomas A
TA
Lamoureux
Ecosse L
EL
Pesudovs
Konrad
K
D000203:Activities of Daily Living; D000368:Aged; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular; D008297:Male; D017063:Outcome Assessment, Health Care; D018918:Phacoemulsification; D019591:Pseudophakia / Q000503:physiopathology; D011594:Psychometrics; D011788:Quality of Life; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires; D014792:Visual Acuity / Q000502:physiology*