Measuring the effectiveness of cataract surgery: the reliability and validity of a visual function outcomes instrument

Abstract

Aims-To assess test-retest reliability and validity of the "TyPE" patient self assessed visual function questionnaire, as part of a study in two hospitals measuring the eVectiveness of cataract surgery. The American TyPE questionnaire had minor adaptations made for use in Britain. Methods-Test-retest reliability was assessed on 63 out of 378 adult cataract surgery patients in the study, using Spearman correlation coeYcients and kappa coeYcients of agreement. "Construct" validity was evaluated by comparing the association between changes in visual function questionnaire scores after surgery, with patients' perception of change in visual function obtained by independent interview of 24 patients. Results-The TyPE questionnaire items showed very good test-retest reliability. Average Spearman and kappa coeYcients for 39 patients from hospital 1 were 0.93 and 0.84 respectively. Spearman and kappa coeYcients of 0.9 and 0.81 were obtained for those nine patients in hospital 2 where both the test and retest questionnaires were filled in by the same people. However, for the 15 patients from hospital 2, where the questionnaire was filled in by diVerent people in the retest, reliability was less good: the Spearman coeYcients were still high, average 0.72, but the kappa coeYcients were poor, 0.27. Good construct validity was exhibited, with a correlation of 0.79 between change in distance vision score from the questionnaires and the independent interview. Conclusions-The adapted TyPE questionnaire is both very reliable and has good construct validity. The kappa coefficient should be used wherever possible to evaluate reliability. The test-retest reliability and validity and practicability of other visual function questionnaires have not been assessed adequately, and further development should be carried out of all such questionnaires, so that they may be introduced into routine clinical care. (Br J Ophthalmol 1999;83:66-70)

Quality-of-life improvements in cataract patients with bilateral blue light–filtering intraocular lenses: Clinical trial

“…1 Because cataract surgery can change patients' QOL, self-assessment of visual function and health-related quality of life (HRQOL) are important outcome measures. 2 A longitudinal study of 552 patients who had first-eye cataract surgery used a 14-item questionnaire that assesses visual function . Eighty-nine percent of patients showed improvement 4 months after surgery.…”

Prospective randomised double-masked trial of bilateral multifocal, bifocal or monofocal intraocular lenses

“…It has been validated for use in the United States as a telephone-administered questionnaire 23 and in the UK for self-administered use. 24 The questions were filled in by the patient, assisted by family or nursing staff as required, between the pre-operative assessment and surgery (pre-op) and just before the post-operative assessment (post-op).…”

Using Rasch analysis to revisit the validity of the Cataract TyPE Spec instrument for measuring cataract surgery outcomes

“…The scoring problem of classical test theory arises from the assumption that distances on the scales are equal over the full range of the scale and the scale is erroneously treated as an interval scale based on the ordinal level of scoring. 12,13 More recently, modern psychometric approaches have been adopted such as the Rasch measurement models. 14- 16 Rasch analysis provides unparalleled insight into content validity and targeting of item difficulty to patient ability, not possible with classical test theory.…”

“…[19][20][21] The Cataract TyPE Spec is a reliable and valid scale, by classical test theory, for measuring vision-related function and outcomes of cataract extraction. 12,13 In view of the limitations of the classic test theory, we sought to use Rasch analysis to revalidate the Cataract TyPE Spec instrument in an Australian cataract population waiting to have cataract extraction. This included, if necessary, making revisions to the content of the instrument to improve its validity.…”

“…2,3 The need to include patient-reported outcomes (or questionnaires) in the assessment of cataract surgery is now widely appreciated. [4][5][6] Several questionnaires developed for this purpose, such as the Activities of Daily Vision Scale (ADVS), 7,8 Visual Disability Assessment (VDA), 9 Visual Function 14 (VF-14), 10 Catquest, 11 and Cataract TyPE Specification (TyPE Spec), 12,13 have used the traditional psychometric approach; that is the classical test theory. However there are 2 important limitations of classical test theory: the validity of the scoring method and the validity of the items included.…”